[Federal Register Volume 62, Number 135 (Tuesday, July 15, 1997)]
[Proposed Rules]
[Pages 37808-37818]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-18357]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 97-NM-79-AD]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 727 Series Airplanes
Modified in Accordance With Supplemental Type Certificate SA1368SO,
SA1797SO, or SA1798SO
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking (NPRM).
-----------------------------------------------------------------------
SUMMARY: This document proposes the adoption of a new airworthiness
directive (AD) that is applicable to certain Boeing Model 727 series
airplanes that have been converted from a passenger to a cargo-carrying
(``freighter'') configuration. This proposal would require limiting the
payload on the main cargo deck by revising the Limitations Sections of
all Airplane Flight Manuals (AFM), AFM Supplements, and Airplane Weight
and Balance Supplements for these airplanes. This proposal also
provides for the submission of data and analysis that substantiates the
strength of the main cargo deck, or modification of the main cargo
deck, as optional terminating action for these payload restrictions.
This proposal is prompted by the FAA's determination that unreinforced
floor structure of the main cargo deck is not strong enough to enable
the airplane to safely carry the maximum payload that is currently
allowed in this area. The actions specified by the proposed AD are
intended to prevent failure of the floor structure, which could lead to
loss of the airplane.
DATES: Comments must be received by August 22, 1997.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 97-NM-79-AD, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056. Comments may be inspected at this location
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal
holidays.
FOR FURTHER INFORMATION CONTACT: Steven C. Fox, Senior Aerospace
Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft
Certification Office, 1601 Lind Avenue, SW., Renton, Washington;
telephone (425) 227-2777; fax (425) 227-1181.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the
proposed rule by submitting such written data, views, or arguments as
they may desire. Communications shall identify the Rules Docket number
and be submitted in triplicate to the address specified above. All
communications received on or before the closing date for comments,
specified above, will be considered before taking action on the
proposed rule. The proposals contained in this notice may be changed in
light of the comments received.
Comments are specifically invited on the overall regulatory,
economic, environmental, and energy aspects of the proposed rule. All
comments submitted will be available, both before and after the closing
date for comments, in the Rules Docket for examination by interested
persons. A report summarizing each FAA-public contact concerned with
the substance of this proposal will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments
submitted in response to this notice must submit a self-addressed,
stamped postcard on which the following statement is made: ``Comments
to Docket Number 97-NM-79-AD.'' The postcard will be date stamped and
returned to the commenter.
Availability of NPRMs
Any person may obtain a copy of this NPRM by submitting a request
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules
Docket No. 97-NM-79-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
The FAA has issued supplemental type certificates (STC) for
converting certain Boeing Model 727 and 747 series airplanes from a
passenger to a cargo-carrying (``freighter'') configuration. These
freighter conversions entail such modifications as removal of the
passenger interior, the installation of systems to handle cargo
containers (such as pallets and other unit load devices), the
installation of a side cargo door for the main cargo deck, and
alterations to such systems as the hydraulic, electrical, and smoke
detection systems that are associated with the transport of cargo. When
a conversion is completed, the weight permitted to be carried
(``payload'') on the main cargo deck is significantly
[[Page 37809]]
greater than the payload allowed in that same area when the airplane
was in its original passenger configuration.
On December 27, 1995, the FAA issued Airworthiness Directive (AD)
96-01-03, amendment 39-9479 (61 FR 116, January 3, 1996). The FAA took
this action after determining that Model 747 passenger airplanes
converted to freighters under certain STC's are not structurally
capable of safely carrying the payload allowed on the main cargo deck.
This condition is due to structural deficiencies in the floor beams of
this deck, as well as in the fuselage structure surrounding the side
cargo door for this area. That AD requires operators of those Model 747
freighters to reduce the maximum payload that can be carried on the
main cargo deck in order ``[t]o prevent collapse of the aft fuselage
due to inadequate strength in the airplane structure and subsequent
separation of the aft fuselage from the airplane.'' Model 747
freighters affected by AD 96-01-03 were converted under STC's held by
GATX/Airlog Company (``GATX'') when that AD was issued. GATX had
acquired the original STC's from Hayes International Corporation
(Hayes).
During its investigation of the circumstances that led to the
issuance of AD 96-01-03, the FAA determined that similar unsafe
conditions were likely to be found on certain Model 727 series
airplanes that had been converted to freighters in a comparable manner.
The bases for these concerns were that similar procedures and design
methods had been used on both the 727 and 747 models, and that these
STC's could be traced back to the same companies.
Actions Subsequent to AD 96-01-03
In response to those concerns, the FAA's Transport Airplane
Directorate established a design review team of FAA engineers to
identify any safety problems pertaining to certain interior and side
cargo door STC's for Model 727 series airplanes, and to make
recommendations for correcting any unsafe conditions.
The design review team has determined that there are more than 10
STC's for Model 727 freighters (``freighter STC's'' or ``Model 727
freighter STC's'') that need to be reviewed. These freighter STC's are
individually held by Aeronautical Engineers, Inc. (AEI), ATAZ, Inc.
(ATAZ), Federal Express Corporation (FedEx), and Pemco Aeroplex, Inc.
(Pemco). The STC's held by AEI are SA1368SO, which pertains to the
cargo door on Model 727-100 series airplanes; SA1797SO, which pertains
to the cargo door on Model 727-200 series airplanes; and SA1798SO,
which pertains to the cargo compartment on Model 727-200 series
airplanes. Over 300 Model 727 series airplanes of both U.S. and foreign
registry have been modified in accordance with these STC's, and more
than 32 operators worldwide use these freighters.
In reviewing these freighter STC's, the design review team applied
the standards of Civil Air Regulations (CAR) part 4b, applicable to the
original Boeing Model 727 airplane. These federal standards establish
minimum safety requirements. A design which does not meet these
standards is presumed to be unsafe.
Between September 1996 and February 1997, members of the design
review team made four visits to inspect Model 727 series airplanes that
were in the process of being converted or already had been converted
under these freighter STC's. Site visits were conducted at Pemco World
Air Services in Dothan, Alabama (Pemco STC's); the Tramco repair
station in Everett, Washington (FedEx STC's that had originally been
developed by Hayes); and Professional Modification Services (PMS),
Inc.'s, facility in Miami, Florida (AEI and ATAZ STC's).
On all of the Model 727 series airplanes inspected during these
site visits, the design review team observed that the original
passenger floor beams, which now support the main cargo deck, had not
been structurally reinforced by the STC modification for the heavier
payloads these freighters are permitted to carry.
These STC freighters typically are allowed to carry 8,000 pound
containers (weight of the cargo and container) on the main cargo deck.
Because these containers are 88 inches long, the running load (the
weight that can be placed on a longitudinal section of the main cargo
deck) is 90 pounds per inch (8,000 pounds divided by 88 inches). This
running load of 90 pounds per inch is a safety concern because it is
approximately 2.6 times higher than the maximum running load of 34.5
pounds per inch allowed on these same floor beams when the airplane was
in a passenger configuration.
FAA Structural Analysis of the Floor Beams of the Main Cargo Deck
The design review team examined the documents that the current or a
previous STC holder had submitted when seeking original FAA approval of
the STC application. The team was unable to find any data to verify
that the unreinforced floor structure of the main cargo deck can safely
support the heavier freighter payloads.
To independently evaluate whether these floor beams are strong
enough to support the maximum payload permitted by the STC's, the
design review team performed a limited structural analysis of the
design of each main cargo deck viewed during its site visits.
In analyzing the floor beams of the main cargo deck, the FAA
engineers used the payload configuration defined in the weight and
balance documents for each STC. (These STC freighters are operated in
accordance with FAA-approved Weight and Balance Supplements, which
specify the payload that can be carried onboard, as well as the maximum
payload and assigned location for individual containers on the main
cargo deck.) Most of the containers permitted in the Weight and Balance
Supplements for these STC's weigh up to 8,000 pounds each.
In its analysis, the design review team considered the different
cargo handling system configurations observed on the STC freighters
during the site visits; these systems include roller trays and
container locks. The roller trays are attached to the floor of the main
cargo deck, and enable cargo to be rolled forward and aft. These trays
also support the weight of the cargo containers. The container locks,
which hold a container in place, are spaced along the floor of the main
cargo deck for all of these STC's but one; that STC also has side
vertical cargo container restraints (``side restraints''). The analysis
is based on the use of containers that are 88 inches by 125 inches, and
the location of the horizontal center of gravity for the total payload
in each container was within 8.8 inches from the geometric center of
the base of the container for the forward and aft direction and 12.5
inches from the geometric center of the base of the container for the
left and right direction.
The design review team used commonly accepted analytical methods in
its structural analyses. This methodology, or an equivalent, was
applicable when the STC application was originally submitted for
approval, and it is applicable today. None of the floor analyses
performed by the team involved the application of advanced technologies
such as finite element modeling. The results of these structural
analyses were consistent with data provided by Boeing, which had
originally built these airplanes as passenger transports, and with some
of the data provided by these STC holders.
To evaluate the adequacy of the floor, the team determined that the
most likely ``critical case'' (the conditions or
[[Page 37810]]
circumstances that exert the greatest forces on the main cargo deck)
would be the ``down gust'' conditions specified in CAR part 4b. Down
gusts are downward vertical movements of air that occur in turbulence
and storms. Down gusts exert a downward force on the entire airplane.
As this force causes the airplane to accelerate downward, containers on
the main cargo deck--because of inertia--are pulled upward. This upward
force on the containers is transmitted through the container locks and
into the floor beams. On these STC freighters, this upward force could
bend these floor beams upward to failure, and the failure of even a
single beam could result in loss of the airplane.
Even if the floor beams of the main cargo deck only become
deformed, the results could be catastrophic. Because flight control
system cables and fuel lines pass through small holes in these floor
beams, significant--although temporary--deformation of these beams
could jam the cables or break fuel lines. Consequently, this could
reduce controllability of the airplane, cause fuel starvation of one or
more engines, or lead to a fire in the fuselage.
The FAA also has determined that performance of the flight
maneuvers defined in CAR part 4b would produce critical case forces on
these STC freighters, and consequent deformation or failure of floor
beams on the main cargo deck. These maneuvers would cause upward forces
on the cargo containers relative to the floor. Because of the location
of the container locks, the floor beams at the forward or aft edges of
the containers would be more critically loaded, and consequently
deflected upward.
Determining Floor Strength (The ``Margin of Safety'')
The measure of the ability of the floor beams of the main cargo
deck to support the stresses caused by various load cases (combinations
of specific container weights with either wind gust conditions or
airplane maneuvers) is its ``margin of safety.'' Because the floor must
be designed to withstand the critical case stresses, the design review
team calculated the margin of safety when the floor is subject to the
turbulent ``down gust'' wind conditions defined in CAR part 4b.
The equation for determining the margin of safety is:
[GRAPHIC] [TIFF OMITTED] TP15JY97.002
In this equation, ``Allowable Stress'' is the measure of the
strength of a floor beam of the main cargo deck. ``Applied Stress'' is
the stress level produced in that floor beam multiplied by a ``factor
of safety'' of 1.5. The weight of the containers on the floor beam,
flight conditions (for example, wind gusts or airplane maneuvers), and
other forces, such as pressurization of the fuselage, all combine to
create the ``applied stress'' level in that floor beam. CAR 4b.200(a)
requires the inclusion of the 1.5 factor of safety in structural
designs. (This factor is discussed in the ``Elimination of the 1.5
Factor of Safety'' section of this preamble.)
When the margin of safety is zero for all load cases, the structure
meets the minimum requirements of CAR part 4b. A structure with a
margin of safety greater than zero exceeds those standards. A structure
with a margin of safety of less than zero does not meet these minimum
requirements, and is presumed to be unsafe. If the margin of safety
reaches -1 (the extreme case), the structure is not strong enough to
withstand the stresses generated by any load case without failing.
Using this equation, the design review team calculated margins of
safety for the STC floor designs as ranging from approximately -0.55 to
-0.63. Because of the large negative margins of safety that were
calculated for the down gust condition (the most likely critical case),
the FAA did not analyze other load cases.
For the margins of safety to be positive for the ``down gust''
condition, the FAA determined that these STC freighters must be limited
to less than 50% of the typical maximum payload of 8,000 pounds per
container currently allowed by the STC's. From its analyses, the design
review team determined that these main cargo decks are capable of
supporting a maximum payload of approximately 3,000 pounds per
container (a maximum running load of 34.5 pounds per inch) in all areas
of the main cargo deck, except in the area adjacent to the side cargo
door. In that side door area, containers would be restricted to a
maximum payload of approximately 2,700 pounds per container (a maximum
running load of 31.0 pounds per inch) due to structural configurations
affecting the strength of the floor beams in this area. These running
loads include payload in the lower lobe cargo compartments, and any
other load applied to the bottom of the floor beams of the main cargo
deck. [The Air Transport Association of America (ATA) recommended a
maximum payload of 6,000 pounds per container. This recommendation,
which is discussed in the ``ATA Recommendations for a Final Rule''
section of this preamble, is substantially above the safe payload
limits calculated by the design review team, and would result in a
negative margin of safety.]
Typically, freighters converted under these STC's are allowed to
carry 11 or 12 containers on the main cargo deck. Containers in most
areas of this deck have a maximum payload of up to 8,000 pounds per
container; over the wing and landing gear area, this maximum payload
per container can be up to 10,000 pounds. Although it would seem that
these STC freighters could carry up to a total of 100,000 pounds, the
maximum payload is actually limited by the strength of the fuselage as
well as the strength of the floor beams. Consequently, the current
maximum payloads on these airplanes range from 54,000 pounds (for a
Model 727-100 series airplane) to 62,000 pounds (for a Model 727-200
series airplane), depending on the configuration of the freighter. The
FAA's structural analysis shows that the maximum payload should be
limited to approximately 35,000 pounds. This maximum payload is
approximately 22% less than the average payload of 45,000 pounds that
has been reported by some operators of these Model 727 STC freighters.
The FAA has determined that none of these main cargo decks are
strong enough for the current maximum payloads, and therefore are
unsafe. Furthermore, these decks do not comply with the requirements of
CAR part 4b.
Operational Factors Affecting Payload Limitation
The FAA's structural analysis was based on the ``worst case''
conditions of the following operational factors: maximum operating
speed limit, airplane in-flight weight, container orientation, and side
restraints. The FAA realizes that if restrictions are placed on these
factors, higher payloads can be allowed. Although the absolute effects
of these restrictions would require extensive analysis, the FAA has
concluded that it is sufficient to estimate the effects of these
factors if they are only to be applied for a limited amount of time.
The FAA design review team determined that these restrictions would not
violate other load cases.
Maximum Operational Speed and In-Flight Weight
Some of these STC freighters are allowed to fly at a maximum
operational speed of 390 knots equivalent airspeed (KEAS). During
turbulence, the forces experienced by the airplane are, in part, a
function of the aircraft's speed, which consequently affects the forces
on the floor beams. By reducing the maximum operational speed to 350
knots indicated
[[Page 37811]]
airspeed (KIAS), the forces on the floor beams during turbulence are
reduced.
The forces experienced by the airplane during turbulence also are a
function of the weight of the aircraft. A heavy airplane has more
inertia, and therefore is less affected by severe gusts than a lighter
one. The FAA has estimated that a minimum operational in-flight weight
of 100,000 pounds will reduce the gust loads on these airplanes and,
therefore, reduce the floor beam loads. Some ways to ensure that the
in-flight weight does not fall below a prescribed limit is to have a
minimum cargo weight, a minimum quantity of ``tankered'' fuel,
sufficient ballast, or a combination of these items.
Container Orientation
Typically, these STC freighters carry National Aerospace Standard
(NAS) 3610 class II cargo containers, which have a fixed back wall; a
partially or fully removable front wall; and are 88 inches by 125
inches. Due to this method of construction, a large portion of the
forces that a container experiences in ``down gust'' wind conditions or
turbulence is carried by the container's back wall, which is its
strongest element. When cargo containers are oriented back-to-back, a
large portion of both container loads is carried by the same container
locks. This places higher loads on the floor beam supporting these
locks. By requiring the containers to be oriented with the door side of
the container facing forward, however, a more uniform distribution of
the loads is achieved.
Side Restraints
A better distribution of the container load is achieved by
installing side restraints. The FAA estimates that there can be an
increase in the maximum payload per container when FAA-approved side
restraints are installed.
The FAA estimates that the combined effect of this speed
limitation, minimum in-flight weight, and container orientation would
result in a total weight of no more than 8,000 pounds for any two
adjacent containers that are each 88 inches by 125 inches. By
installing FAA-approved side restraints, this estimated total weight
for any two adjacent containers could be increased to 9,600 pounds.
Under no circumstances, however, can the total weight of any individual
container exceed 8,000 pounds.
Elimination of the 1.5 Factor of Safety
At the request of industry, the FAA considered the consequences of
elimination of the 1.5 factor of safety used in the ``Margin of
Safety'' equation discussed above. By eliminating the 1.5 factor of
safety, the FAA analysis determined that the proposed payload limits
per container would increase by 50%. CAR 4b.200(a) requires that an
airplane be designed with a certain amount of ``reserve structural
strength'' to minimize the potential for complete structural failure of
an airplane. This reserve is the ``1.5 factor of safety.'' Ordinarily,
an applicant seeking to reduce or eliminate this requirement must file
a request for an exemption. If the applicant uses an approach in its
design that is comparable to the 1.5 factor of safety, the applicant
can declare that this approach provides ``an equivalent level of
safety.'' The applicant, however, must substantiate this declaration to
the satisfaction of the FAA.
The FAA has examined the consequences resulting from the
elimination of the 1.5 factor of safety, and has concluded that this
action would pose unacceptable hazards for these airplanes. The FAA's
intent in issuing this proposed AD is to prevent a combination of
circumstances that could result in catastrophic loss of a Model 727
freighter converted under these STC's. Elimination of the 1.5 factor of
safety in conjunction with the other measures discussed earlier to
increase the allowable payload would be contrary to this intent.
CAR part 4b refers to the critical load cases--the down gust and
maneuver forces previously described in this preamble--as ``limit
loads.'' CAR 4b.200 requires that these limit loads be multiplied by
1.5 (the ``1.5 factor of safety''), thereby becoming ``ultimate loads''
as defined in CAR part 4b. CAR 4b.201(c) further requires that the
structure be able to carry these ultimate loads (which provide a
reserve of structural strength) without failure. Although it is
anticipated that these STC freighters will not be routinely subjected
to limit load forces, it sometimes happens during emergencies and
unusual environmental conditions such as turbulence.
Emergency Conditions
In an emergency, the pilot may exceed critical case maneuver
forces, and fly the STC freighter beyond the airspeed and flight
maneuver limits for which the airplane is designed. The failure of an
engine, avoidance of a collision, or the opening of a cargo door during
flight are conditions that could necessitate these actions.
Emergencies do occur. On February 5, 1997, a Model 727 passenger
airplane was flying to John F. Kennedy International Airport in New
York when an Air National Guard F-16 jet fighter approached close
enough to activate the Model 727's collision avoidance system alarm.
The pilot of the passenger airplane, following the system's emergency
guidance, maneuvered the Model 727 into a steep dive and then a steep
climb. Two flight attendants and a passenger were thrown down by these
maneuvers. Although the actual maneuver forces for this incident are
unknown, the 1.5 factor of safety may have provided structural strength
to maneuver the airplane beyond the forces in CAR part 4b.
In 1991, a pilot performed a flight maneuver that imposed forces of
approximately 3g's (three times the force of gravity) on a Model 747
freighter that was carrying a partial payload. The applicable federal
regulations require Model 747 and 727 series airplanes to be designed
for maneuvers imposing forces of up to 2.5g's. Had this freighter been
carrying a full payload and the 1.5 factor of safety not been used in
its design, FAA analysis indicates that this freighter would have been
lost.
Turbulence
Airplanes may encounter severe turbulence that exerts wind gust
forces beyond the critical case forces of CAR part 4b. AD 96-01-03
describes an occasion in 1991 when wind gusts were so severe that an
engine separated from a Model 747-100 freighter shortly after take-off.
More recently, severe wind gusts on September 5, 1996, caused
numerous passenger injuries and one fatality on a Model 747-400 series
airplane. The FAA received reports indicating that those gusts produced
downward accelerations of -1.15g's and upward accelerations of +2.09g's
on that airplane in less than four seconds. Had a Model 727 STC
freighter experienced similar conditions while transporting close to
the maximum payload, FAA analysis indicates that the floor beams of the
freighter's main cargo deck would have collapsed.
The FAA has received 87 reports of Model 727 series airplanes
experiencing severe turbulence; these reports typically do not include
events that have occurred in other countries. The majority of these
events were unforeseen and resulted in injuries to the flight crew or
passengers. Five of the reports document gusts causing airplane
accelerations of at least +1.88g's upward and -1.5g's downward.
[[Page 37812]]
Hazardous Deformation of the Main Cargo Deck
CAR 4b.201(a) requires any structure on the freighter, including
the floor beams, to be strong enough to withstand--without
``detrimental permanent deformation''--the anticipated critical case
forces that could be exerted upon it during its service life. CAR
4b.201(b) requires that any structural deformations caused by these
critical case or limit loads not interfere with the safe operation of
the airplane. (The catastrophic consequences of deformation are
discussed earlier in this preamble.) Using the 1.5 factor of safety in
structural analysis takes deformation into account; without the 1.5
factor of safety, the STC holder would be required to provide an
analysis that demonstrates these floors would be free from detrimental
deformation. Because these STC's lack a deformation analysis, the FAA
would not consider a request for reducing the 1.5 factor of safety
requirement unless such an analysis was conducted.
Other Considerations
Another reason that reserve structural strength is necessary is
that aerodynamic and structural analysis theory is not precise: exact
conditions or circumstances are indeterminable; therefore
approximations must be made. In addition, the 1.5 factor of safety
takes into account such considerations as the variations in the
physical properties of materials, the range of fabrication tolerances,
and corrosion or damage. For example, all Model 727 series airplanes
must have enough structural reserve to cover the corrosion control
activities mandated by AD 90-25-03, amendment 39-6787 (55 FR 49258,
November 27, 1990). That AD, in order to control corrosion, permits up
to 10% of the material thickness of a floor beam of the main deck to be
removed by grinding without undertaking repair; the removal of this
material further reduces the strength of the floor.
The majority of these modified airplanes are nearing, or past,
their design life of 20 years, 60,000 flights, or 50,000 hours of
operation. As the airplanes age and are repeatedly flown, they
accumulate fatigue damage and corrosion, which degrades the structural
capability. Airplanes that are near or past their design life are part
of the FAA's Aging Airplane Program and are subject to numerous AD's to
correct unsafe conditions resulting from fatigue cracking and
corrosion.
During the time period allowed by the AD's to implement the
corrective action, it is probable that many of these aging airplanes
will continue to have fatigue cracks and corrosion. Because these
airplanes have been built with a safety factor of 1.5, there is a
sufficient structural strength margin to allow some finite time to
implement the AD's to correct the unsafe conditions. Without this
factor of safety, a new maintenance program would have to be developed
for these airplanes to ensure that all of the Aging Airplane Program
fatigue cracks and corrosion problems are continuously identified and
immediately eliminated.
Service History of the Model 727 STC Freighters
Although the modification of these airplanes commenced in 1983, the
average modification date for these STC freighters is 1991. In fact,
approximately 100 of these airplanes (one-third of the STC freighter
fleet) have been modified in just the last three years.
Most of these STC freighters fly only two flights each day,
resulting in a low number of accumulated flights since conversion. A
representative of the largest operator of these airplanes indicates
that, on average, the airplanes carry only slightly more than half of
the current maximum payload of 8,000 pounds per container. These
circumstances may explain why the FAA has not received reports of
adverse events relating to the structural strength of these floor
beams.
These floor beams, if overstressed, are not likely to give warning
prior to total failure. The existing floor beams on these STC
freighters are commonly made from 7075-T6511 aluminum alloy, and there
is only a 10% difference between the stress level at which the floor
beam permanently bends, and the stress level at which the beam breaks.
Consequently, once the floor beams are stressed to the point of being
permanently bent, it takes only a small amount of additional stress
until the floor beams break, which could result in loss of the
airplane.
The FAA has concluded that the reported service history of these
STC freighters does not demonstrate that these airplanes are safe.
Issuance of an AD Is Appropriate Regulatory Action
Because of the unsafe condition found on these STC freighters (the
inadequate strength of the floor structure of the main cargo deck to
carry the current maximum payloads), the FAA has determined that there
are two ways in which it could proceed: Issuance of an AD to correct
the unsafe condition of the floor, or suspension or revocation of these
STC's.
The Administrator of the FAA has the authority to issue an AD when
``an unsafe condition exists in a product'' [14 CFR 39.1(a)], and
``[t]hat condition is likely to exist or develop in other products of
the same type design'' [14 CFR 39.1(b)]. When such a finding is made,
the Administrator may, as appropriate, prescribe ``inspections and the
conditions and limitations, if any, under which those products may
continue to be operated'' (14 CFR 39.11). By using the AD process, the
FAA can still allow these STC freighters to operate, although under
restrictions which are necessary to eliminate the unsafe condition.
Because the floor structures did not meet CAR part 4b certification
standards at the time these STC's were originally issued, the
Administrator of the FAA is empowered to suspend or revoke these STC's
[49 U.S.C. 44709(b)]. If the Administrator were to take such action
against these STC's, the order could result in the immediate grounding
of these STC freighters.
In consideration of the disruption of domestic and international
commerce that would result from the suspension or revocation of these
STC's, as well as the significant impacts on the domestic and
international economy that such an action would have, the FAA has
concluded that the issuance of an AD with restrictions on the maximum
payloads on the main cargo deck is appropriate action. These payload
restrictions will enable these freighters to continue operating, and
remove the unsafe condition that currently exists in the floor beams of
the main cargo deck.
FAA Meetings With STC Holders and Operators
The FAA has met individually with each of the affected STC holders
to discuss the FAA design review team's observations, analyses, and
findings. In a letter sent prior to these meetings, the FAA provided
its preliminary conclusions to each STC holder. In addition, the agency
asked the STC holder to submit data showing that unsafe conditions do
not exist, and that the STC designs do meet applicable federal aviation
regulations. If the FAA's findings and analyses could not be
controverted, the STC holder was asked to specify what actions it would
take to bring its designs into compliance. STC holders also were asked
to propose actions that would enable these airplanes to operate safely
while data or modifications were being developed.
At its meeting with the FAA, AEI did not present any information to
[[Page 37813]]
contradict the FAA's analyses, or submit proposals to keep these planes
operating safely. The FAA's meetings with the other 3 STC holders
produced similar results.
The FAA also has met jointly with the STC holders and the operators
of the Model 727 freighters modified under these STC's. On February 14,
1997, the FAA convened this meeting, which was attended by more than 75
industry representatives, to discuss what the design review team had
observed during its site visits and determined from its analyses of STC
data. During this meeting the operators presented no technical data,
but provided the FAA with information about the potential impacts on
their businesses if the agency were to reduce the current maximum
payload.
Industry Proposal for the Timing of an NPRM and FAA Response
During the February 14 meeting, representatives of the affected
operators and STC holders in attendance presented a proposal to the
FAA. Generally, industry proposed that the FAA delay issuing an NPRM
and imposing payload restrictions; in turn, industry, within 120 days
from the end of February 1997, would test floor beams, perform
analyses, redesign the floor structure, if necessary, and submit data
to the FAA substantiating compliance with CAR part 4b. At the meeting,
the FAA responded that its priority is the safety of these airplanes,
and the burden is now on industry to establish the ability of these STC
freighters to carry more than the 3,000 pounds per container being
considered by the FAA.
ATA Recommendations for a Final Rule
ATA followed up on the proposal at the February 14 meeting with a
March 10, 1997, letter that contained recommendations in order ``to get
the necessary design changes quickly incorporated while permitting the
airlines to continue operating their aircraft.'' ATA proposed that a
3,000 pound per pallet weight limit be gradually phased-in as follows:
1. There would be at least 120 days after the effective date of the
AD before any payload restrictions would be implemented. According to
ATA, this period would enable STC holders or others to redesign the
freighter floors and provide enough time for operators to procure parts
to modify the floors.
2. Initially, payload restrictions would be reduced from 8,000
pounds per pallet to 6,000 pounds per pallet. These restrictions would
be in effect for at least one year or the next ``C'' check, whichever
occurs later, and operators would not be required to modify the floor
beams during this time.
3. Ultimately, the floor beams of the main cargo deck would not
have to be modified until at least 16 months after the effective date
of the AD. At that time, the payload per pallet would be reduced to
3,000 pounds if an operator opted not to accomplish that modification.
4. Airplanes would not be subject to any of these restrictions if
operators can substantiate to the FAA that the floor beams are strong
enough to support the existing payload per pallet.
The FAA considered ATA's recommendations in developing this
proposed action. The FAA determined that allowing these airplanes to
continue to operate without restrictions for 120 days after the
effective date of this AD, and allowing 16 months for modification of
the floor structure of the main cargo deck would not address the unsafe
condition in a timely manner. The FAA's analysis also determined that
ATA's recommended payload limit of 6,000 pounds per container at all
locations would result in negative margins of safety. The interim
weight restrictions proposed by the FAA allow the carriage of a limited
number of individual containers at or above the 6,000 pound per
container payload suggested by ATA. In addition, the 120-day period of
operation at the interim payloads proposed by the FAA (discussed below)
does, in part, meet ATA's suggested time for allowing redesign of these
STC freighter floors.
FAA Findings
Based on the observations and analyses of its design review team,
and information presented by affected STC holders and the operators of
Model 727 series airplanes converted to freighters under these STC's,
the FAA has found that:
1. None of the floor beams of the main cargo deck on any of these
STC's have been modified from the original passenger configuration to
support the heavier payloads carried on a freighter.
2. Based on the FAA's analyses, the floor structures of these STC
freighters are not capable of withstanding the forces that would result
from the current maximum payload when CAR part 4b conditions are
encountered.
3. When the maximum payload of a container is limited to 8,000
pounds or 6,000 pounds (for all container positions) as proposed by
ATA, the margins of safety for the floor beams of the main cargo deck
are calculated as negative numbers and the structural strength of these
beams is not sufficient to meet the requirements of CAR part 4b. When
the maximum payload of a container is limited to approximately 3,000
pounds, the margin of safety is calculated as a positive number and
these floor beams meet the structural strength requirements of CAR part
4b.
4. The FAA estimates the combined effect of imposing operational
restrictions on airplane weight, maximum operating speed, and
orientation of containers reduces the forces exerted on the airplane in
``down gust'' conditions, and will permit the maximum payload of a
container to be increased on an interim basis. The installation of side
restraints can permit a further temporary increase in payload.
5. Typically, these STC freighters are modified by other STC's that
change the maximum taxi, take-off, zero fuel, and landing weights of
these airplanes. These weight changes permit the airplanes to carry
more payload on the main cargo deck.
No compatibility study has been performed showing that these weight
changes are safe considering the existing freighter STC modifications
and payload limits. In addition, no compatibility study has been done
for the addition of auxiliary fuel tanks, engine changes, and other
types of modifications that alter the basic loads on these airplanes.
6. When these STC modifications were accomplished, each airplane
was modified differently, due to different installer shop practices and
the configuration of each airplane prior to modification. Subsequent
modifications under other STC's that alter the structure were not shown
to be compatible with the freighter modifications. The resulting
airplane configuration can be significantly different between
individual airplanes. Any modifications that are undertaken to bring
these airplanes into compliance with CAR part 4b must be shown to be
compatible with the specific airplanes being modified.
7. The elimination of the 1.5 factor would not eliminate the unsafe
condition that occurs when these airplanes are carrying containers
weighing more than the payloads specified in this proposed AD.
FAA Conclusions
From these findings, the FAA has concluded that:
1. The lack of strength in the floor structure of the main cargo
deck must be corrected by reducing the payload carried on the main
cargo deck. This reduced payload includes the payload in the lower lobe
cargo compartments.
[[Page 37814]]
2. Maximum payloads of approximately 2,700 pounds per container in
the areas near the forward side cargo door and approximately 3,000
pounds per container in all other areas of the main cargo deck provide
an acceptable level of safety. It is estimated that operational
restrictions on airplane weight, maximum operating speed, and
orientation of containers, as well as the installation of FAA-approved
side restraints, would allow safe operation with higher payloads during
an interim period.
3. Because these STC freighters are modified by other STC's that
change the maximum taxi, take-off, zero fuel, and landing weights of
these airplanes, and permit more payload on the main cargo deck, all of
the airplanes' Airplane Flight Manuals (AFM's), AFM Supplements, and
Weight and Balance Supplements would have to be revised to show the
payload restrictions.
Additional AD Actions
The FAA design review team's scope of review of these STC's was not
limited to concerns about the strength of the floor structure that
support the main cargo deck. The team also made inspections and
gathered information about other areas where additional unsafe
conditions may exist. Following this proposed rulemaking, additional
rulemaking will be initiated to address these concerns. These concerns
include the following structural, door systems, and STC certification
and documentation issues:
Structural Deficiencies
Lack of ``Fail-Safe'' Hinges on the Cargo Door
The design review team saw single or double-piece hinge fittings on
the side cargo doors of these STC freighters. Should a crack propagate
along the hinge line where the hinge attaches either to the upper sill
of the fuselage or to the door itself, the cargo door could separate
from the airplane, and result in loss of the airplane.
Apparent Lack of Strength of the Structure Surrounding the Side Cargo
Door
To install a side cargo door for the main deck, an opening of
approximately 7.5 feet by 11 feet (82.5 square feet) must be cut into
the side of the fuselage. This opening requires that the cutout area
and adjacent structural areas be substantially reinforced. If the
fuselage structure that surrounds this cargo door is not strong enough
to withstand the forces that may be exerted during flight, it could
result in loss of the airplane.
The design review team observed that reinforcing structures used in
this area, such as longerons, frames, doublers and triplers, are
discontinuous and appear to lack adequate load paths and strength.
These discrepancies could result in a fuselage structure that does not
meet the strength and deformation requirements of CAR 4b.201, proof of
structure standards of CAR 4b.202, or fail safety requirements of CAR
4b.270(b).
In its examination of the data supporting these STC's, the design
review team determined that the STC applicants used inadequate methods
and/or incomplete analyses to substantiate that their modifications
provide adequate strength in this area. The STC applicants typically
did not substantiate the strength of numerous structural features, such
as splices and runouts. The STC holders also used analytical approaches
that failed to consider such impacts as redistribution of the forces in
the fuselage, and localized stress effects such as ``buckling.''
Inadequate Cargo Restraint Barriers
CAR 4b.260 requires that the restraint barrier in the cargo
compartment of the main deck be strong enough to protect the occupants
from injury when the freighter is carrying its maximum payload and
emergency landing conditions occur (the ``9.0g standard'').
Based on the observations and analyses of the design review team,
the FAA has determined that the bulkhead restraint barriers on all of
the observed STC freighters do not meet the 9.0g standard; three of the
four STC holders have confirmed the FAA's finding.
Deficiencies in Systems for the Side Cargo Door
Because of cargo door-related accidents, industry and the FAA,
during the early 1990s, conducted an extensive design review of cargo
doors and agreed on new standards to eliminate safety deficiencies in
certain cargo door systems. The FAA agreed to issue AD's requiring
compliance with these standards, which are based on Amendment 54 to 14
CFR 25.783, for those freighters that did not comply. These standards
are not intended to upgrade the requirements of CAR part 4b after
certification, but are to correct potentially unsafe conditions on
airplanes already in service that were identified during the design
review.
Inadequate Warning System for an ``Unsafe'' Door
Freighters must have a warning system that directly alerts the
pilot and co-pilot that the side cargo door is ``unsafe'' (open,
unlatched, or unlocked). A ``safe'' cargo door is one that is verified
to be closed, latched, and locked prior to taxiing for take-off.
The design review team observed STC freighters that do not have a
red cargo door warning light in plain view of both pilots. In the event
that the cargo door is unsafe, pilots on those planes would not be
directly warned; this situation could lead to pilot inaction or
dispatch of the airplane, and consequent opening of this door during
flight.
Improper Pressurization of the Fuselage When the Cargo Door Is
``Unsafe''
The opening of a door during flight has caused several serious
accidents. Some of those accidents have resulted in loss of life;
others have resulted in loss of the airplane. Consequently, industry
and the FAA adopted standards to prevent pressurization of the fuselage
when the cargo door is unsafe. Typically, compliance with these
standards involves installation of vent doors that close only when the
cargo door is safe.
In its examination of the associated cargo door related systems on
these STC freighters, the design review team detected that the fuselage
of some of these airplanes could be pressurized when the cargo door
vent door is not closed. The team also found that some STC's did not
have the required safety analysis that would verify the adequacy of the
design's pressurization prevention system when the cargo door is
unsafe.
Electrical/hydraulic System Deficiencies That Could Cause an ``Unsafe''
Cargo Door
Electrical short circuits could transmit power to the electrical or
hydraulic systems that operate the side cargo door, lead to opening of
this door during flight, and could result in the loss of the airplane.
To prevent this, all power to this door must be removed during flight,
and the flight crew must not be able to restore this power at any time
during flight.
CAR 4b.606 (which has been further refined by the cargo door
standards agreed upon by industry and the FAA) requires STC holders to
show that the design of the electrical system is adequate to prevent
the side cargo door from opening during flight. These STC holders did
not accomplish this analysis.
Inability to Visually Verify the Status of the Side Cargo Door
When the system that warns the pilot and co-pilot about an
``unsafe'' cargo door is not working correctly, the red warning light
either will fail to light up
[[Page 37815]]
during pre-flight testing of the system, or will light up when the side
cargo door is actually ``safe.'' These STC's have a backup system that
allows the flight crew to confirm that the door is actually safe.
The cargo door standards to which industry and the FAA agreed
require ``a visual means of directly inspecting the locks.'' The design
review team observed that these backup systems enable the flight crew
to view only a portion of the locking beam. Because a visual means of
directly inspecting the locking mechanism of the door is not available,
these STC's do not comply with these standards. When the entire locking
mechanism cannot be visually inspected, a false report on the condition
of the door may be given to the crew, and the airplane may be
dispatched with an unsafe door.
Cargo Compartment Smoke Detection and Warning Systems
CAR 4b.383(e)(2) requires that there be a means for the flight crew
to check and assure the proper functioning of each smoke detector
circuit. The FAA design review team and STC freighter operators have
observed that some STC's contain electrical wiring designs that test
only a portion of the smoke detection system--not the entire system as
required--when a single button is pressed (the ``press to test''
feature). If the flight crew is not alerted that some smoke detectors
are not functioning, the crew may not be able to respond to a cargo
compartment fire in a timely manner.
The Carriage of Supernumeraries
Supernumeraries are non-flight crew personnel who are carried on
board the airplane. For example, a supernumerary could be an airline
employee who is not part of the flight crew, but is specially trained
to handle cargo.
These STC freighters have a cargo compartment that is used only for
the carriage of cargo. Before supernumeraries can be carried, the STC
holder or operator must apply to the FAA for an exemption from CAR
4b.383(e), and from other federal regulations that pertain to seats,
berths, and safety belts; emergency evacuation; ventilation; and fire
protection. Such exemptions are granted only when the FAA determines
that the design contains features that provide an acceptable level of
safety for the supernumeraries.
The FAA has become aware of numerous instances where STC holders
have made provisions for the carriage of supernumeraries without
applying for FAA exemptions and without demonstrating that the safety
provisions for supernumeraries are acceptable.
STC Data and Documentation Concerns
When the FAA design review team evaluated data that STC applicants
originally submitted to obtain FAA approval of these freighter STC's,
the team found a number of deficiencies. Examples include data that is
not adequately substantiated; payload limits in Weight and Balance
documents that are inconsistent with the structural capability of the
fuselage; structural analyses that lack the critical case; no analysis
of the floor beams over the wing center section; and documented
negative margins of safety that are unresolved.
Unsubmitted Instructions for Continued Airworthiness
Federal regulations require an STC holder to submit ``Instructions
for Continued Airworthiness'' to the FAA for review. These instructions
include maintenance procedures, maintenance manuals, and maintenance
program requirements for the continued safety of the airplane converted
under the STC. Only one of the four STC holders has complied with this
requirement.
Future FAA Review of Other Transport Airplane Cargo Conversions
The FAA's review of STC's and the safety of airplanes converted
from a passenger to a cargo-carrying configuration will not be limited
to just Model 727 and 747 series airplanes. Based on the discovery of
unsafe conditions on both of these airplane models, the FAA intends to
examine all transport category passenger airplanes that have been
converted to a cargo-carrying configuration under STC's.
The FAA urges STC holders and operators of these freighters to
begin, as soon as possible, an examination of the data supporting the
STC's. If problems such as those identified in the Model 727 and 747
conversions are detected, corrective actions should be developed. Self-
examination of these conversions prior to formal FAA review may shorten
the time needed for any corrective actions, and reduce the impacts on
operators of these freighters.
Explanation of Requirements of Proposed Rule
Since an unsafe condition has been identified that is likely to
exist or develop on other products of this same type design, the
proposed AD would restrict the payload on the main cargo deck of Model
727 series airplanes modified in accordance with STC SA1368SO, STC
SA1797SO, or SA1798SO. This proposal would be accomplished by revisions
to the Limitations Section of all FAA-approved AFM's, AFM Supplements,
and Weight and Balance Supplements. Revision of all these documents
would be required because these STC freighters have been modified by
other STC's that change the maximum taxi, take-off, zero fuel, and
landing weights of these airplanes.
The payload limits that are proposed are based on the use of
containers that are 88 inches by 125 inches, and a horizontal center of
gravity for the total payload in each container that is located within
8.8 inches from the geometric center of the base of the container for
the forward and aft direction and 12.5 inches from the geometric center
of the base of the container for the left and right direction. The
payload limits are also based on a requirement that all containers are
loaded with the door side of the container facing forward.
The proposal presents three options for payload limitations: one
``baseline'' [paragraph (a)] and two ``interim'' [paragraphs (b) and
(c)], depending upon the floor configuration and other operating
limitations.
Paragraph (a) would establish a payload limit of 3,000 pounds per
container.
For airplanes equipped with FAA-approved side restraints, paragraph
(b) would provide for temporary payload limits in some areas of 9,600
pounds for any two adjacent containers, with a limit of 8,000 pounds
for any one container. These limits would be available when the
following two conditions are met: the maximum operational airspeed does
not exceed 350 KIAS and the minimum in-flight weight exceeds 100,000
pounds.
For airplanes that are not equipped with FAA-approved side
restraints, paragraph (c) would provide for a temporary payload limit
in some areas of 8,000 pounds for any two adjacent containers. This
limit also would be available when the following two conditions are
met: the maximum operational airspeed does not exceed 350 KIAS and the
minimum in-flight weight exceeds 100,000 pounds.
Because the determination of the effects of operational limitations
on payload is based on approximations, the resulting payload limits may
be unconservative. Consequently, operation with these payload limits is
only acceptable for a limited period of time. Continued use of these
operational limits and the associated payload limits must be
substantiated. The FAA has determined that an acceptable level of
safety is provided if the time period is
[[Page 37816]]
limited to no more than 120 days, which would also allow sufficient
time for an applicant to develop an acceptable analysis regarding the
applicability of the operational limitations.
At the February 14 meeting discussed above, the industry
participants proposed to complete a redesign of the floor structure
within 120 days from the end of February (by the end of June). The FAA
bases the proposed 120-day interim period in paragraphs (b) and (c) on
the following assumptions:
1. Industry will fulfill this proposal;
2. The final rule will not become effective before October 1, 1997,
and thus allow additional time for the industry to modify the main
cargo deck floor structure; and
3. Operators and STC holders will work diligently in the meantime
to avoid any disruptions to operations.
In light of the seriousness of the unsafe conditions addressed by
this proposal, the FAA considers that the 120-day interim period:
1. Provides an acceptable level of safety;
2. Minimizes exposure to any potential unconservatism in the
determination of the payload limits;
3. Provides an adequate opportunity for applicants to develop
substantiation for continued use of operational limits to enhance
payload limits; and
4. Minimizes, for the interim period, the burdens on operators
resulting from this AD.
Should an operator desire to transport containers of other
dimensions or use a different payload container center of gravity, it
would have to apply to the FAA for appropriate payload limits.
At any time, an applicant would be able to present a proposal to
modify the floor structure or proposed weight and other limits, data,
and analysis to the FAA to substantiate that floor structure of the
main cargo deck (existing or modified) is in compliance with the
requirements of CAR part 4b when supporting the proposed weight limits.
When the FAA determines that these documents are acceptable, the
operator would be able to operate its airplane at the payload limits
substantiated by its data and analysis.
Regulatory Evaluation Summary
The regulations proposed herein would not have substantial direct
effects on the States, on the relationship between the national
government and the States, or on the distribution of power and
responsibilities among the various levels of government. Therefore, in
accordance with Executive Order 12612, it is determined that this
proposal would not have sufficient federalism implications to warrant
the preparation of a Federalism Assessment.
The FAA conducted a ``Cost Analysis and Initial Regulatory
Flexibility Determination and Analysis'' to determine the regulatory
impacts of this and three other proposed AD's to operators of all 244
U.S.-registered Boeing Model 727-100 and -200 series passenger
airplanes that have been converted to cargo-carrying configurations
under 10 STC's held by four companies. This analysis is included in the
docket for each AD. The FAA has determined that approximately 20 Model
727-100 and 37 Model 727-200 series airplanes operated by 13 carriers
were converted under AEI STC's. (There were 15 Model 727 series
airplanes for which the FAA could not identify the STC holder. It is
possible that these airplanes were also converted under an AEI STC.
Their costs are not included here.)
Assuming that the operators of affected airplanes converted under
AEI STC's would comply with the restricted interim operating conditions
set forth in the proposed rule, the FAA estimates in the analysis that
each Model 727-100 series airplane modified under the AEI STC's would
lose approximately $32,504 in revenues during the 120-day interim
period after the effective date of the proposed AD. Further, the FAA
estimates that none of the modified Model 727-200 series airplanes
would lose revenues during the interim period.
Based on the ``Cost Analysis and Initial Regulatory Flexibility
Determination and Analysis'' included in the docket, the FAA estimates
that affected airplanes could be modified at a cost of $100,000 per
airplane. The total cost, therefore, to modify the fleet of affected
Model 727 series airplanes that were originally modified to the AEI
STC's is $6.4 million. This assumes that modifications to the airplane
are available and installed within the 120-day time period. If there
are any delays in the availability or implementation of modifications,
the revenue loss due to operation at the 3,000-pound payload limit
would substantially increase the costs. The FAA solicits detailed cost
information from the affected carrier concerning the proposed AD's
compliance costs.
The Regulatory Flexibility Act of 1980 (RFA) was enacted by
Congress to ensure that small entities are not unnecessarily or
disproportionately burdened by government regulations. The RFA requires
a Regulatory Flexibility Analysis if a proposed rule would have a
significant economic impact, either detrimental or beneficial, on a
substantial number of small entities. The Regulatory Flexibility
Analysis includes the consideration of alternative actions.
FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance,
establishes threshold cost values and small entity size standards for
complying with RFA review requirements in FAA rulemaking actions. The
Order defines ``small entities'' in terms of size thresholds,
``significant economic impact'' in terms of annualized cost thresholds,
and ``substantial number'' as a number which is not less than eleven
and which is more than one-third of the small entities subject to the
proposed or final rule.
FAA Order 2100.14A sets the size threshold for small entities
operating aircraft for hire at 9 aircraft and the annualized cost
threshold at $69,000 for scheduled operations of airplanes with fewer
than 60 seats and $5,000 for nonscheduled operations.
Eight of the 13 affected carriers operating 16 affected airplanes
are considered small entities (i.e., each operates fewer than 9
affected airplanes). The cost of the proposed AD greatly exceeds the
threshold values defined in the FAA Order. The proposed AD does not
affect a substantial number of small entities, however, because it is a
number less than eleven. Therefore, this AD does not have an
significant economic impact on a substantial number of small entities
and a regulatory flexibility analysis is not required.
For the reasons discussed above, I certify that this proposed
regulation (1) Is not a ``significant regulatory action'' under
Executive Order 12866; (2) is not a ``significant rule'' under the DOT
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);
and (3) if promulgated, will not have a significant economic impact,
positive or negative, on a substantial number of small entities under
the criteria of the Regulatory Flexibility Act. A copy of the ``Cost
Analysis and Initial Regulatory Flexibility Determination and
Analysis'' prepared for this action is contained in the Rules Docket. A
copy of it may be obtained by contacting the Rules Docket at the
location provided under the caption ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Airplanes, Aviation safety, Safety.
The Proposed Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration proposes to amend
part
[[Page 37817]]
39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39--AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
Boeing: Docket 97-NM-79-AD.
Applicability: Model 727 series airplanes; modified in
accordance with Supplemental Type Certificate SA1368SO, SA1797SO, or
SA1798SO; certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
otherwise modified, altered, or repaired in the area subject to the
requirements of this AD. For airplanes that have been modified,
altered, or repaired so that the performance of the requirements of
this AD is affected, the owner/operator must request approval for an
alternative method of compliance in accordance with paragraph (g) of
this AD. The request should include an assessment of the effect of
the modification, alteration, or repair on the unsafe condition
addressed by this AD; and, if the unsafe condition has not been
eliminated, the request should include specific proposed actions to
address it.
Compliance: Required as indicated, unless accomplished
previously.
To prevent structural failure of the floor beams of the main
cargo deck, which could lead to loss of the airplane, accomplish the
following:
(a) Except as provided in paragraphs (b), (c), and (d) of this
AD, within 48 clock hours (not flight hours) after the effective
date of this AD, accomplish the requirements of paragraph (a)(1) or
(a)(2) of this AD, as applicable:
(1) For airplanes on which only containers that are 88 inches by
125 inches are transported: Revise the Limitations Section of all
FAA-approved Airplane Flight Manuals (AFM) and AFM Supplements, and
the Limitations Section of all FAA-approved Airplane Weight and
Balance Supplements to include the following information. This may
be accomplished by inserting a copy of this AD in all AFM's, AFM
Supplements, and Weight and Balance Supplements.
``Limitations
All containers must be oriented with the door side of the
container facing forward.
The location of the horizontal center of gravity for the total
payload within each container shall not vary more than 8.8 inches
from the geometric center of the base of the container for the
forward and aft direction and 12.5 inches from the geometric center
of the base of the container for the left or right direction.
Payload Limitations
Do not exceed a total weight of 3,000 pounds per container on
the main cargo deck, except in the area adjacent to the side cargo
door. In that side door area (Body Station 440 to Body Station 660),
containers are restricted to a maximum payload of 2,700 pounds per
container. This payload limit includes the payload in the lower lobe
cargo compartments and any other load applied to the bottom of the
floor beams of the main cargo deck for the same body station
location as the container on the main cargo deck.''
(2) For airplanes on which any containers other than 88 inches
by 125 inches are transported: Revise the Limitations Section of all
FAA-approved AFM's and AFM Supplements, and the Limitations Section
of all FAA-approved Airplane Weight and Balance Supplements in
accordance with a method approved by the Manager, Standardization
Branch, ANM-113, FAA Transport Airplane Directorate.
Note 2: The weight restrictions to be approved under paragraph
(a)(2) will be consistent with the applicable weight restrictions of
paragraph (a)(1), (b), or (c) of this AD.
(b) During the period ending 120 days after the effective date of
this AD: For airplanes on which only containers that are 88 inches by
125 inches are transported, and that are equipped with side vertical
cargo container restraints that have been approved by the Manager,
Standardization Branch, ANM-113, as an optional alternative to
compliance with paragraph (a)(1) of this AD, revise the Limitations
Section of all FAA-approved AFM's and AFM Supplements, and the
Limitations Section of all FAA-approved Airplane Weight and Balance
Supplements to include the following limitations. This may be
accomplished by inserting a copy of this AD in all AFM's, AFM
Supplements, and Weight and Balance Supplements.
``Limitations
Maximum Operating Airspeed of Vmo equals 350 knots
indicated airspeed (KIAS).
Minimum in-flight weight: 100,000 pounds or greater.
All containers must be oriented with the door side of the
container facing forward.
The location of the horizontal center of gravity for the total
payload within each container shall not vary more than 8.8 inches
from the geometric center of the base of the container for the
forward and aft direction and 12.5 inches from the geometric center
of the base of the container for the left or right direction.
Payload Limitations
Do not exceed a total weight of 9,600 pounds for any two
adjacent containers and a total weight of 8,000 pounds for any
container, except that the total weight of all containers forward of
Body Station 436 shall not exceed 4,000 pounds. This payload limit
includes the payload in the lower lobe cargo compartments and any
other load applied to the bottom of the floor beams of the main
cargo deck for the same body station location as the container on
the main cargo deck.
(c) During the period ending 120 days after the effective date
of this AD: For airplanes on which only containers that are 88
inches by 125 inches are transported, and that are NOT equipped with
side vertical cargo container restraints that have been approved by
the Manager, Standardization Branch, ANM-113, as an optional
alternative to compliance with paragraph (a)(1) of this AD,
accomplish the following: Revise the Limitations Section of all FAA-
approved AFM's and AFM Supplements, and the Limitations Section of
all FAA-approved Airplane Weight and Balance Supplements to include
the following limitations. This may be accomplished by inserting a
copy of this AD in all AFM's, AFM Supplements, and Weight and
Balance Supplements.
``Limitations
Maximum Operating Airspeed of Vmo equals 350 knots
indicated airspeed (KIAS).
Minimum in-flight weight: 100,000 pounds or greater.
All containers must be oriented with the door side of the
container facing forward.
The location of the horizontal center of gravity for the total
payload within each container shall not vary more than 8.8 inches
from the geometric center of the base of the container for the
forward and aft direction and 12.5 inches from the geometric center
of the base of the container for the left or right direction.
Payload Limitations
Do not exceed a total weight of 8,000 pounds for any two
adjacent containers and the total weight of all containers forward
of Body Station 436 shall not exceed 4,000 pounds. This payload
limit includes the payload in the lower lobe cargo compartments and
any other load applied to the bottom of the floor beams of the main
cargo deck for the same body station location as the container on
the main cargo deck.''
(d) For airplanes that operate under the 350 KIAS requirements
of paragraph (b) or (c) of this AD: A maximum operating airspeed
limitation placard must be installed adjacent to the airspeed
indicator and in full view of both pilots. This placard must state:
``Limit Vmo to 350 KIAS.''
(e) For airplanes complying with paragraph (b) or (c) of this
AD, within 120 days after the effective date of this AD: Revise the
Limitations Section of all FAA-approved AFM's and AFM Supplements,
and the Limitations Section of all FAA-approved Airplane Weight and
Balance Supplements to include the following information. This may
be accomplished by inserting a copy of this AD in all AFM's, AFM
Supplements, and Weight and Balance Supplements.
``Limitations
All containers must be oriented with the door side of the
container facing forward.
The location of the horizontal center of gravity for the total
payload within each container shall not vary more than 8.8 inches
from the geometric center of the base of the container for the
forward and aft direction and 12.5 inches from the geometric center
of the base of the container for the left or right direction.
[[Page 37818]]
Payload Limitations
Do not exceed a total weight of 3,000 pounds per container on
the main cargo deck, except in the area adjacent to the side cargo
door. In that side door area (Body Station 440 to Body Station 660),
containers are restricted to a maximum payload of 2,700 pounds per
container. This payload limit includes the payload in the lower lobe
cargo compartments and any other load applied to the bottom of the
floor beams of the main cargo deck for the same body station
location as the container on the main cargo deck.''
(f) As an alternative to compliance with paragraphs (a), (b),
(c), (d), and (e) of this AD: An applicant may submit a proposal to
modify the floor structure or proposed new payload and other limits,
and substantiating data and analyses to the Manager, Standardization
Branch, ANM-113, in accordance with the procedures of paragraph (g)
of this AD, showing that the floor structure of the main cargo deck
is in compliance with the requirements of Civil Air Regulations
(CAR) part 4b. If the FAA determines that these documents are
acceptable and applicable to the specific airplane being analyzed
and approves the proposed limits, prior to flight under these new
limits, the operator must revise the Limitations Section of all FAA-
approved AFM's and AFM Supplements, and the Limitations Section of
all FAA-approved Airplane Weight and Balance Supplements in
accordance with a method approved by the Manager, Standardization
Branch, ANM-113. Accomplishment of these revisions in accordance
with the requirements of this paragraph constitutes terminating
action for the requirements of this AD.
(g) An alternative method of compliance or adjustment of the
compliance time that provides an acceptable level of safety may be
used if approved by the Manager, Standardization Branch, ANM-113.
Operators shall submit their requests through an appropriate FAA
Principal Maintenance Inspector who may add comments and then send
it to the Manager, Standardization Branch, ANM-113.
Note 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Manager, Standardization Branch, ANM-113.
(h) Special flight permits may be issued in accordance with
sections 21.197 and 21.199 of the Federal Aviation Regulations (14
CFR 21.197 and 21.199) to operate the airplane to a location where
the requirements of this AD can be accomplished.
Issued in Renton, Washington, on July 8, 1997.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 97-18357 Filed 7-14-97; 8:45 am]
BILLING CODE 4910-13-U
