[Federal Register Volume 62, Number 139 (Monday, July 21, 1997)]
[Proposed Rules]
[Pages 38945-38948]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-19104]
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Proposed Rules
Federal Register
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This section of the FEDERAL REGISTER contains notices to the public of
the proposed issuance of rules and regulations. The purpose of these
notices is to give interested persons an opportunity to participate in
the rule making prior to the adoption of the final rules.
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Federal Register / Vol. 62, No. 139 / Monday, July 21, 1997 /
Proposed Rules
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM-135; Notice No. SC-96-8A-NM]
Special Conditions: Boeing, Model 767-27C Airplanes, Airborne
Warning and Control System (AWACS) Modification; Liquid Oxygen System
AGENCY: Federal Aviation Administration (FAA), DOT.
ACTION: Supplemental notice of proposed special conditions.
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SUMMARY: This notice revises an earlier proposal for special conditions
for Boeing Model 767-27C airplanes modified by installation of an
Airborne Warning and Control System (AWACS). These airplanes will be
equipped with an oxygen system utilizing liquid oxygen (LOX). The
applicable regulations do not contain adequate or appropriate safety
standards for the design and installation of oxygen systems utilizing
LOX for storage. This action revises the original proposal to address
certain recommended additional requirements for the LOX system. The
revised standards are intended to ensure that the design and
installation of the liquid oxygen system is such that a level of safety
equivalent to that established by the airworthiness standards for
transport category airplanes is provided.
DATES: Comments must be received on or before August 11, 1997.
ADDRESSES: Comments on this proposal may be mailed in duplicate to:
Federal Aviation Administration, Office of the Assistant Chief Counsel,
Attention: Rules Docket (ANM-7), Docket No. NM-135, 1601 Lind Avenue
SW, Renton, Washington 98055-4056; or delivered in duplicate to the
Office of the Assistant Chief Counsel at the above address. Comments
must be marked: Docket No. NM-135. Comments may be inspected in the
Rules Docket weekdays, except Federal holidays, between 7:30 a.m. and
4:00 p.m.
FOR FURTHER INFORMATION CONTACT:
William Schroeder, FAA, Standardization Branch, ANM-113, Transport
Airplane Directorate, Airplane Certification Service, 1601 Lind Avenue
SW, Renton, Washington 98055-4056; telephone (425) 227-2148.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of
these proposed special conditions by submitting such written data,
views, or arguments as they may desire. Communications should identify
the regulatory docket or notice number and be submitted in duplicate to
the address specified above. All communications received on or before
the closing date for comments will be considered by the Administrator
before further rulemaking action is taken on these proposals. The
proposals contained in this notice may be changed in light of comments
received. All comments submitted will be available in the Rules Docket
for examination by interested persons, both before and after the
closing date for comments. A report summarizing each substantive public
contact with FAA personnel concerning this rulemaking will be filed in
the docket. Persons wishing the FAA to acknowledge receipt of their
comments submitted in response to this notice must submit with those
comments a self-addressed, stamped postcard on which the following
statement is made: ``Comments to Docket No. NM-135.'' The postcard will
be date stamped and returned to the commenter.
Background
On November 21, 1996, the FAA published notice in the Federal
Register (61 FR 59202) of proposed special conditions for Boeing Model
767-27C airplanes modified to an AWACS configuration. The special
conditions are proposed requirements for design and installation of a
liquid oxygen (LOX) system. These special conditions are considered
necessary to provide the appropriate design and installation criteria
required to assure safety of the LOX system.
The Department of the Air Force, commenting to the docket by
letter, recommended additional requirements for design and installation
of the LOX system. Based on some of those recommendations, the FAA has
revised special conditions f. and m. By this notice, the comment period
is reopened to allow interested persons to comment on the additional
requirements.
Discussion of Comments
One commenter, the Department of the Air Force, Headquarters
Aeronautical Systems Center, responded to the request for comments,
providing the following comments and recommended additions/changes to
the identified paragraphs of the proposed special conditions. Those
recommended additions/changes are prompted by U.S. Air Force past
experience with LOX systems in other airplanes. The proposed special
conditions addressed by the comments, the relevant comments, and the
FAA's assessment and conclusions are as follows:
Special Condition b. The liquid oxygen converter shall be located
in the airplane so that there is no risk of damage due to an
uncontained rotor or fan blade failure.
The commenter agrees with the special condition but has additional
concerns. The commenter advises that the Department of the Air Force
would require inspection of the compartment or zone in the airplane
which contains the LOX converter and heat exchanging equipment to
ensure that no buildup of flammable vapors may occur. The commenter
states minor leakage of LOX systems fittings is a common problem
because of the cold LOX and gas temperature effects on the metal
fittings. The commenter further states that the buildup of gaseous
oxygen in combination with flammable vapors in an airplane compartment
is a serious concern, and therefore recommends that the compartment
have adequate ventilation and smoke detectors that will alert the
flightcrew in case of fire. If the LOX converter is located in the
lower lobe, the commenter recommends that inflight access to this
compartment be provided. The commenter further states that for USAF
AWACS airplanes they have also recommended that safety equipment,
including fire extinguisher(s) and portable protective breathing
equipment, be provided. A recharger outlet to refill the portable
protective breathing equipment is advisable, says the commenter, or the
[[Page 38946]]
protective breathing device should have 30 minutes minimum oxygen
supply.
The FAA agrees with the commenter's concern for LOX fittings and
the buildup of oxygen in combination with flammable fluids, and access
to the compartment containing the LOX converter. Much of these concerns
are addressed in proposed special conditions a, c, e, g, h, and l. The
special conditions do not require total shrouding and drainage of all
LOX fittings, but depends on dilution of oxygen to reduce the hazard.
In that respect, the FAA notes that the LOX converter is installed in
the aft lower lobe of the airplane (classified as an electronic
equipment bay), and inflight access is provided. Ventilation to this
bay is considered adequate at 1000 to 3000 cubic feet per minute to
preclude the hazardous accumulation of oxygen in the event of LOX
converter or line leaks. Additionally, Sec. 25.1451 requires that
oxygen equipment and lines be installed so that escaping oxygen cannot
cause ignition of grease, fluid, or vapor accumulations that are
present in normal operation or as a result of failure or malfunction of
any system. The FAA considers that the special conditions, as proposed,
provided adequate protection to address the concerns expressed by the
commenter and therefore does not consider that additional requirements
are necessary in this regard.
The FAA does not concur with the commenter regarding the
requirements for fire extinguishers, portable breathing equipment, and
smoke detectors. The lower lobes of the 767-27C are classified as
electronic equipment bays; therefore, there is no requirement to
provide cargo bay liners, smoke detections, or fire suppression
systems. Carry-on cargo is not permitted in either lower lobe unless it
is stored in containers providing fire protection equivalent to that
afforded by Class D cargo or baggage compartments. The installed AWACS
mission/electronic equipment in these bays contains very small
quantities of smoke-producing materials, and most are installed in
metal cabinets. With regard to the Liquid Oxygen System located in the
aft lower lobe, if a leak occurred in this system, a hazardous
concentration of oxygen should be precluded by the large amount of
ventilation (1,000 cfm minimum to 3,000 cfm with the outflow valve
open). If a catastrophic failure of the LOX system occurred, a smoke
detector would not reduce this danger as the smoke would occur only
after the oxygen-enriched fire ignited.
Special Condition c. The liquid oxygen system and associated
gaseous oxygen distribution lines should be designed and located to
minimize the hazard from uncontained rotor debris.
The commenter requests specific safety practices to be followed in
the design and installation of oxygen lines in the proximity of heat-
generating equipment and other lines carrying flammable fluid or
electrical wires and components. The FAA does not disagree with these
practices, but considers that the existing standards (i.e.,
Secs. 25.1451, 25.1309(a), 25.1309(b), and 25.1453) already define safe
practices.
Special Condition d. The flight deck oxygen system shall meet the
supply requirements of part 121 after the distribution line has been
severed by a rotor fragment.
The commenter states that this requirement is not clear. The FAA
notes that the published version of the proposed special conditions
contained a typographical error in that the word ``severed'' was
printed as ``served,'' and this may have led to the confusion. This
special condition requires that an adequate supply of oxygen be
available to the flightcrew after cutting any line in the rotor burst
area, and is clear with the spelling corrected. The commenter also
notes military oxygen requirements concerning multiple oxygen supplies
that are not relevant to this installation and states that the
flightcrew should have control of the oxygen system. The FAA notes that
the requirement for flightcrew control of the oxygen system is
addressed in Sec. 25.1445(a)(2).
The commenter further states that one flight crewmember, such as
the flight engineer, should be designated as the crewmember responsible
for the oxygen system. The FAA has no requirement for this in gaseous
oxygen systems and sees no reason to require it as a special condition
for LOX systems. The commenter states that the AWACS crewmembers should
have oxygen dispensing and breathing equipment comparable to that
provided to the flightcrew (i.e., pressure demand breathing equipment).
The FAA is evaluating the crewmembers' oxygen dispensing equipment in a
separate issue paper, and will not address it in the Special Conditions
under discussion.
Special Condition e. The pressure relief valves on the liquid
oxygen converters shall be vented overboard through a drain in the
bottom of the airplane. Means must be provided to prevent hydrocarbon
fluid migration from impinging upon the vent outlet of the liquid
oxygen system.
The commenter concurs with the requirement for venting and draining
the LOX converter and recommends certain safety procedures during the
servicing of the LOX. Servicing of the LOX is not addressed in the
airworthiness standards for transport category airplanes and is
therefore considered beyond the scope of the notice.
Special Condition f. The system shall include provisions to ensure
complete conversion of the liquid oxygen to gaseous oxygen.
The commenter agrees with the requirement to completely convert the
liquid oxygen to gaseous oxygen, but advocates a specific requirement
that the converted gas be no more than 20 deg. F less than cabin
ambient temperature under the conditions of maximum demand for normal
use of the oxygen system. The FAA agrees with the commenter and
proposes to revise Special Condition f. to add the following sentence:
``The resultant oxygen gas must be delivered to the first oxygen outlet
for breathing such that the temperature is no more than 20 deg. F less
than the cabin ambient temperature under the conditions of the maximum
demand or flow of oxygen gas for normal use of the oxygen system.''
The commenter expressed another concern regarding Special Condition
f., which would require that the LOX converter include a ``line valve''
that would enable the flightcrew to shut down flow from the LOX
converter, should a severed or broken line allow LOX to spill into the
airplane. The FAA concurs with this concern and proposes to add the
following sentence to Special Condition f: ``A LOX shutoff valve shall
be installed on the main oxygen distribution line prior to any
secondary lines. The shutoff valve must be compatible with LOX
temperatures and be readily accessible (either directly if manual, or
by remote activation if an automatic valve).''
Special Condition j. Oxygen system components shall be burst
pressure tested to 3.0 times, and proof pressure tested to 1.5 times,
the maximum normal operating pressure. Compliance with the requirement
for burst testing may be shown by analysis, or a combination of
analysis and test.
The commenter gives background information on a manufacturer of LOX
converters, and advises that a rupture disk be included on the outer
shell of the converter. The FAA does not wish to regulate a design
solution when other designs (e.g., designing the outer shell with
pressure capability equivalent to the inner shell) could satisfy the
requirements of Sec. 25.1309(b).
The commenter also discusses the advantages of dual pressure relief
valves (failure redundancy and flow rate requirements). The FAA agrees
that
[[Page 38947]]
there is an advantage in case one valve fails, but again does not wish
to regulate a design solution when other design implementations could
satisfy the design requirements of Sec. 25.1309(b). The FAA also does
not agree that two valves are required for flow rate requirements, as
this is dependent on valve sizing.
Special Condition k. Oxygen system components shall be electrically
bonded to the airplane structure.
The commenter concurs with this condition, but states that it
requires that the system be tested to ensure that the Ohm rating from
any component on the LOX system will not exceed that which would
preclude static discharging. The FAA will evaluate the applicant's type
design data to ascertain suitability of process and testing of
electrical bonding, but does not consider it necessary to specify the
Ohm level that the bonding is tested to in the special condition.
Special Condition l. All gaseous or liquid oxygen connections
located in close proximity to an ignition source shall be shrouded and
vented overboard using the system specified in (e) above.
The commenter provided the same comments for this special condition
as for Special Condition b. See FAA response to comments on Special
Condition b.
Special Condition m. A means will be provided to indicate the
quantity of oxygen in the converter and oxygen availability to the
flightcrew.
The commenter agrees with the requirement for oxygen quantity
indication and oxygen availability indication to the flightcrew and
notes the desirability of a low level oxygen warning light due to LOX
converter failure modes. In addition, the commenter notes that oxygen
quantity indication should be based on volume and not on pressure,
since the system will essentially operate at a constant pressure until
it is nearly out of oxygen, as opposed to a gaseous oxygen system which
depletes quantity at a linear rate (measuring pressure).
The FAA concurs with the requirement for a low LOX level caution
annunciation and proposes to add the following sentence to Special
Condition m: ``A low LOX level amber caution annunciation will be
furnished to the flightcrew prior to the LOX converter oxygen level
reaching the quantity required to provide sufficient oxygen for
emergency descent requirements.'' The commenter also recommends a
built-in test function so that the flight crew can ascertain that the
low LOX level caution annunciation is functional. The FAA does not
consider it necessary to require this as a Special Condition as it is
adequately addressed in Sec. 25.1309(d)(4).
As a result of these comments, and as discussed earlier in this
document, the FAA has modified special conditions f. and m. from that
proposed in Notice SC-96-8-NM. Public comment is therefore invited on
these additional requirements.
Certification flight testing of the Model 767-27C by Boeing is
imminent. For this reason, and because a delay would significantly
affect the remainder of the certification schedule for the Model 767-
27C, the public comment period for this supplemental notice is
shortened to 20 days.
Special conditions, as appropriate, are issued in accordance with
Sec. 11.49 of the FAR after public notice, as required by Sec. 11.28
and Sec. 11.29(b), and become part of the type certification basis in
accordance with Sec. 21.101(b)(2).
Special conditions are initially applicable to the model for which
they are issued. Should the applicant apply for a supplemental type
certificate to modify any other model included on the same type
certificate to incorporate the same novel or unusual design feature,
the special conditions would apply to the other model under the
provisions of Sec. 21.101(a)(1).
Conclusion
This action affects only certain novel or unusual design features
on one model series of airplane. It is not a rule of general
applicability and affects only the applicant who applied to the FAA for
approval of these features on the airplane.
List of Subjects in 14 CFR Part 25
Aircraft, Aviation Safety, Reporting and recordkeeping
requirements.
The authority citation for these special conditions is as follows:
49 U.S.C. 106(g), 40113, 44701, 44702, 44704.
The Proposed Special Conditions
Accordingly, the Federal Aviation Administration (FAA) proposes the
following special conditions as part of the type certification basis
for Boeing Model 767-27C airplanes modified to an AWACS configuration:
a. The liquid oxygen converter and other oxygen equipment shall not
be installed where baggage, cargo, or loose equipment are stored
(unless items are stored within an appropriate container which is
secured or restrained by acceptable means).
b. The liquid oxygen converter shall be located in the airplane so
that there is no risk of damage due to an uncontained rotor or fan
blade failure.
c. The liquid oxygen system and associated gaseous oxygen
distribution lines should be designed and located to minimize the
hazard from uncontained rotor debris.
d. The flight deck oxygen system shall meet the supply requirements
of Part 121 after the distribution line has been severed by a rotor
fragment.
e. The pressure relief valves on the liquid oxygen converters shall
be vented overboard through a drain in the bottom of the airplane.
Means must be provided to prevent hydrocarbon fluid migration from
impinging upon the vent outlet of the liquid oxygen system.
f. The system shall include provisions to ensure complete
conversion of the liquid oxygen to gaseous oxygen. The resultant oxygen
gas must be delivered to the first oxygen outlet for breathing such
that the temperature is no more than 20 deg.F less than the cabin
ambient temperature under the conditions of the maximum demand or flow
of oxygen gas for normal use of the oxygen system. A LOX shutoff valve
shall be installed on the main oxygen distribution line prior to any
secondary lines. The shutoff valve must be compatible with LOX
temperatures and be readily accessible (either directly if manual, or
by remote activation if automatic).
g. If multiple converters are used and manifold together, check
valves shall be installed so that a leak in one converter will not
allow leakage of oxygen from any other converter.
h. Flexible hoses shall be used for the airplane system connections
to shock-mounted converters, where movement relative to the airplane
may occur.
i. Condensation from system components or lines shall be collected
by drip pans, shields, or other suitable collection means and drained
overboard through a drain fitting separate from the liquid oxygen vent
fitting, as specified in (e) above.
j. Oxygen system components shall be burst pressure tested to 3.0
times, and proof pressure tested to 1.5 times, the maximum normal
operating pressure. Compliance with the requirement for burst testing
may be shown by analysis, or a combination of analysis and test.
k. Oxygen system components shall be electrically bonded to the
airplane structure.
l. All gaseous or liquid oxygen connections located in close
proximity to an ignition source shall be shrouded and vented overboard
using the system specified in Special Condition e. above.
m. A means will be provided to indicate the quantity of oxygen in
the converter and oxygen availability to the flightcrew. A low LOX
level amber caution annunciation will be furnished
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to the flight crew prior to the LOX converter oxygen level reaching the
quantity required to provide sufficient oxygen for emergency descent
requirements.
Issued in Renton, Washington, on July 14, 1997.
Gary L. Killion,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service, ANM-100.
[FR Doc. 97-19104 Filed 7-18-97; 8:45 am]
BILLING CODE 4910-13-M
