[Federal Register Volume 64, Number 224 (Monday, November 22, 1999)]
[Rules and Regulations]
[Pages 63615-63622]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-30138]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 99-NM-147-AD; Amendment 39-11302; AD 99-19-13]
RIN 2120-AA64
Airworthiness Directives; British Aerospace Model HS 748 Series
Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment adopts a new airworthiness directive (AD),
applicable to certain British Aerospace Model HS 748 series airplanes,
that requires revising the Airplane Flight Manual (AFM) to include
requirements for activation of the airframe pneumatic deicing boots.
This amendment is prompted by reports of inflight incidents and an
accident that occurred in icing conditions where the airframe pneumatic
deicing boots were not activated. The actions specified by this AD are
intended to ensure that flightcrews activate the pneumatic wing and
tail deicing boots at the first signs of ice accumulation. This action
will prevent reduced controllability of the aircraft due to adverse
aerodynamic effects of ice adhering to the airplane prior to the first
deicing cycle.
EFFECTIVE DATE: December 27, 1999.
ADDRESSES: Information pertaining to this rulemaking action may be
examined at the Federal Aviation Administration (FAA), Transport
Airplane Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton,
Washington.
FOR FURTHER INFORMATION CONTACT: Norman Martenson, Aerospace Engineer,
Manager, International Branch, ANM-116, FAA, Transport Airplane
Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056;
telephone (425) 227-2110; fax (425) 227-1149.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations (14 CFR part 39) to include an airworthiness
directive (AD) that is applicable to certain British Aerospace Model HS
748 series airplanes was published in the Federal Register on July 16,
1999 (64 FR 38319). That action proposed to require revising the
Airplane Flight Manual (AFM) to include requirements for activation of
the airframe pneumatic deicing boots.
Related Proposals
In addition to the proposed rule described previously, in June
1999, the FAA issued 18 other similar proposals that address the
subject unsafe condition on various airplane models (see below for a
listing of all 19 proposed rules). These 18 proposals also were
published in the Federal Register on July 16, 1999. (Docket 99-NM-153-
AD, for Fokker Model F27 Mark 100, 200, 300, 400, 500, 600, and 700
series airplanes, was also issued as a supplemental notice of proposed
rulemaking, and published in the Federal Register on August 6, 1999.)
This final rule contains the FAA's responses to all relevant public
comments received for each of these proposed rules.
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Manufacturer airplane model Number Federal Register citation
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Cessna Aircraft Company Models 500, 99-NM-136-AD 64 FR 38374
550, and 560 Series Airplanes.
Sabreliner Corporation Models 40, 60, 99-NM-137-AD 64 FR 38358
70, and 80 Series Airplanes.
Gulfstream Aerospace Model G-159 Series 99-NM-138-AD 64 FR 38341
Airplanes.
McDonnell Douglas Models DC-3 and DC-4 99-NM-139-AD 64 FR 38325
Series Airplanes.
Mitsubishi Heavy Industries Model YS-11 99-NM-140-AD 64 FR 38371
and YS-11A Series Airplanes.
Gulfstream American (Frakes Aviation) 99-NM-141-AD 64 FR 38355
Model G-73 (Mallard) and G-73T Series
Airplanes.
Lockheed, Models L-14 and L-18 Series 99-NM-142-AD 64 FR 38338
Airplanes.
Fairchild Models F-27 and FH-227 Series 99-NM-143-AD 64 FR 38322
Airplanes.
Aerospatiale Models ATR-42/ATR-72 99-NM-144-AD 64 FR 38368
Series.
Jetstream Model BAe ATP Airplanes...... 99-NM-145-AD 64 FR 38351
Jetstream Model Airplanes 4101......... 99-NM-146-AD 64 FR 38335
British Aerospace Model HS 748 Series 99-NM-147-AD 64 FR 38319
Airplanes.
Saab Model SF340A/SAAB 340B/SAAB 2000 99-NM-148-AD 64 FR 38365
Series Airplanes.
CASA Model C-212/CN-235 Series 99-NM-149-AD 64 FR 38348
Airplanes.
Dornier Model 328-100 Series Airplanes. 99-NM-150-AD 64 FR 38332
Lockheed Model Series Airplanes 1329-23 99-NM-151-AD 64 FR 38316
and 1329-25 (Lockheed Jetstar).
de Havilland Model DHC-7/DHC-8 Series 99-NM-152-AD 64 FR 38362
Airplanes.
Fokker Model F27 Mark 100/200/300/400/ 99-NM-153-AD 64 FR 42870
500/600/700/050 Series Airplanes.
Short Brothers Model SD3-30/SD3-60/SD3- 99-NM-154-AD 64 FR 38329
SHERPA Airplanes.
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Comments
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the following comments received.
1. Support for the Rule
One commenter supports the proposed rule.
2. Request To Withdraw the Proposal: No Unsafe Condition
Several commenters request that the proposal be withdrawn because
no unsafe condition exists on certain airplanes. One of these
commenters states that the FAA is merely speculating that the proposed
Airplane Flight Manual (AFM) revision will improve safety. Further, the
commenter contends that the FAA cannot substantiate that the proposed
AFM revision will prevent ice bridging. This same commenter also asks
if the FAA met its own standards by testing the
[[Page 63616]]
proposed procedure on each of the affected airplanes.
The FAA does not concur that no unsafe condition exists. As
discussed in the preamble of the proposed rule, the FAA has reviewed
the icing-related incident history of certain airplanes, and has
determined that icing incidents may have occurred because pneumatic
deicing boots were not activated at the first evidence of ice
accretion. As a result, the handling qualities or the controllability
of the airplane may have been reduced due to the accumulated ice. The
FAA also discussed an accident that occurred as a result of the failure
of the flightcrew to activate the wing and tail pneumatic deicing
boots.
Although there may have been no reported cases of incidents or
accidents on a specific airplane model, the potential still exists for
reduced controllability of all airplanes equipped with pneumatic
deicing boots due to adverse aerodynamic effects of ice adhering to the
airplane. This AD addresses this unsafe condition.
Further, ice bridging of deicing boots was considered during
development of the proposed rule. A broad representation of the
aviation community was consulted, including airframe manufacturers, air
carriers, airline pilot associations, airplane owner associations,
deicing boot manufacturers, and National Aeronautics and Space
Administration (NASA). Also, articles readily accessible by the general
piloting community solicited operational information concerning ice
bridging of deicing boots. The FAA considers that the general consensus
of the aviation community is that little or no evidence exists of ice
bridging of deicing boots with current deicing boot designs, and ice
that is not shed after the initial boot cycle continues to increase in
thickness and sheds during subsequent cycles.
In addition, many airplanes equipped with pneumatic deicing boots
to protect the engine are operated when icing conditions are present,
i.e., visible moisture and a specific temperature are observed. As
discussed in Comment #3 (following this response), at least two
airplane manufacturers have issued AFM's that contain procedures to
activate the deicing boots at the first sign of ice accumulation. The
FAA is unaware of any ice bridging problems associated with early
operations of either the airfoil or engine pneumatic deicing boots.
In response to the commenter's question regarding the FAA meeting
its own standards, the FAA infers that the commenter is requesting the
basis for the FAA's determination that the proposed procedures are
safe. Most aircraft certification programs have not considered the
reduced controllability of the aircraft due to adverse aerodynamic
effects of ice adhering to the pneumatic boots. The requirements of
this AD (activation of the deicing boot system at the first sign of ice
formation anywhere on the aircraft, or upon annunciation from an ice
detector system, whichever occurs first, along with the periodic
cycling of the boots) will minimize the ice accretions and thereby
reduce the adverse aerodynamic effects.
3. Request To Withdraw the Proposal: Possible Adverse Effects of
Residual Ice
Several commenters state that deicing boots do the best job of
shedding ice on a single cycle, if ice is permitted to accrete to \1/4\
or \1/2\ inch before activation of the boots. One of these commenters
further contends that the effect of continuous cycling in auto mode may
not produce a clean shed of ice on each activation, and that residual
ice must be taken into consideration before any revision to the AFM is
required. Another commenter states that, although operation in the
continuous mode upon first indication of ice accretion would eliminate
the problem of identification of accretion, the commenter is concerned
that there would then be a potential for degraded performance due to
residual ice.
The FAA does not concur that the proposal should be withdrawn
because of concerns over residual ice. Operation of pneumatic deicing
boots typically results in persistent ice accretions on the boot
surfaces, even when \1/4\ to \1/2\ inch of ice is allowed to accrete
prior to activation of the boots. The persistent residual and inter-
cycle ice accretions typically result in adverse aerodynamic effects
and degraded airplane flying qualities. Activation of the wing and tail
pneumatic deicing boots at the first sign of ice accretion, or at the
annunciation of an ice detector system and periodic operation of the
deicing boots will also result in persistent ice accretions. However,
the proposed procedure will minimize the residual and intercycle ice
accretions because the ice will be shed when the minimum thickness or
mass required for shedding is reached. The residual and intercycle ice
accretion thickness resulting from this procedure is less than the ice
accretion thickness typically recommended prior to operation of the
pneumatic deicing boot. Adverse airplane flying qualities resulting
from ice accretions typically are affected by the thickness, shape,
texture, and location of the ice accretion.
At least two airplane manufacturers have issued AFM's that contain
procedures to activate the deicing boots at the first sign of ice
accumulation. Those two airplane models have different wing and
stabilizer design characteristics and different deicing boot
configurations. Further, those two airplane models represent a large
proportion of the airplane fleet equipped with pneumatic deicing boots.
The FAA has received no reports indicating any adverse effects of
residual ice resulting from early activation of the deicing boots for
these airplane designs.
In addition, a number of airplane models are equipped with deicing
boot systems that include automatic operating modes, wherein the boots
automatically cycle at specific time intervals after being activated.
This automatic cycling has surely resulted in operation of the boots
with less than the recommended thickness of ice accreted. The FAA has
received no reports indicating any adverse effects resulting from the
use of the automatic mode.
4. Request to Withdraw or Delay: Develop More Data
Several commenters request that the FAA delay issuance of the rule
until more data are developed and reviewed. Certain of these commenters
also state that at the public meeting on icing (February 2-4, 1999),
the consensus was that a uniform procedure cannot be adopted for all
airplanes. That is, a ``blanket'' proposal for numerous airplanes
(regardless of design) is inappropriate without specific consideration
for the individual designs. Another one of these commenters points out
that each airplane model is unique and that the operating instructions
for the ice protection system for one airplane model may not be
appropriate for another airplane model. That commenter further adds
that the airframe manufacturer is in the best position to determine
appropriate limitations.
Another one of the commenters requests that, if the proposal is not
withdrawn, the issuance of any rulemaking be delayed since certain
language of the requirements of the AD is confusing.
The FAA does not concur that a delay in issuing this action is
appropriate. The FAA concurs that the airframe manufacturers present at
the February public meeting did not support a common procedure for the
operation of deicing boots. However, as mentioned previously, there
have been no adverse reports on the airplane fleet equipped with
pneumatic deicing boots that
[[Page 63617]]
operate the boots at the first sign of ice accretion. With the
exception of ``older'' pneumatic boots (reference comment #7, below),
the FAA finds that a common procedure for boot operation is
appropriate. The FAA has determined that the common procedures for
operation of deicing boots as required by this AD (activation of the
deicing boot system at the first sign of ice formation anywhere on the
aircraft, or upon annunciation of an ice detector system, whichever
occurs first, and periodic cycling of the boots) will minimize the ice
accretions and thereby reduce the adverse aerodynamic effects.
To withdraw or delay this AD would be inappropriate since the FAA
has determined that an unsafe condition exists, and that the required
AFM revision must be accomplished to ensure continued safety of the
fleet. The fact that other data may be developed at a later time does
not negate the FAA's responsibility to address the existing identified
unsafe condition in a timely manner. No change is necessary to the
final rule in this regard.
The FAA is unable to respond to one commenter's statement that
certain language of the proposal was confusing since no example was
specified.
5. Request To Withdraw Proposals for Certain Airplanes
Three commenters, all airframe manufacturers, request that the
proposal be withdrawn for several airplane models [British Aerospace
Model ATP airplanes, British Aerospace Model HS 748 airplanes, Dornier
Model 328-100 series airplanes, and deHavilland Model DHC-7/DHC-8
series airplanes] since they have been certified to be in compliance
with part 25 of the Federal Aviation Regulations (14 CFR 25.1419).
Additionally, the commenters point out that those airplanes have been
certificated in accordance with the appropriate foreign civil
airworthiness authorities. The commenters further explain that service
experience of those airplanes does not indicate any deficiencies with
regard to handling and performance due to airframe accreted ice. In
conclusion, the commenters state that, in the absence of any evidence
to suggest deficiencies regarding this subject, they cannot support the
intent of the rule.
The FAA acknowledges that an airplane model may have design
characteristics that mitigate the adverse airplane flying qualities
resulting from ice accretion on deicing boot surfaces. As discussed in
the proposal for this AD, the FAA has previously requested that
interested persons provide information on icing system design and
operations procedures concerning flight during icing conditions. The
request also asked manufacturers, who are in the best position to
determine those operating procedures, to provide data showing that
their aircraft have safe operating characteristics with ice accreted on
the protected surfaces (boots). That information was requested
specifically by letter on October 1, 1998, to certain manufacturers of
airplanes certified in accordance with part 25 of the Federal Aviation
Regulations (14 CFR part 25). Except as discussed in Item 6 of the
comment section of this final rule, no other information received
caused the FAA to reconsider that an unsafe condition may exist, or
that a revision of the AFM, such as required by this AD, was unsafe for
those airplanes.
Additionally, similar information was specifically requested in the
discussion section of the proposed rule. Of the comments to the
proposal that were received by the FAA, no additional data was included
for Dornier Model 328-100 series airplanes, or de Havilland Model DHC-
7/DHC-8 series airplanes that caused the FAA to reconsider the previous
conclusion that an unsafe condition exists. Further, no data was
provided to indicate that the proposal to require activation of wing
and tail pneumatic deicing boots at the first sign of ice accretion or
annunciation of an ice detector system was unsafe for any particular
airplane model.
United Kingdom Accident Investigation Board Preliminary Report EWC
91/18 indicated that, while on climb to 16,000 feet in the vicinity of
Oxford, England, on August 11, 1991, a British Aerospace Model ATP
airplane suffered a significant degradation of flying qualities and
propeller icing. According to that report, the deicing boots of the
airplane were not activated, and the airplane stalled, experienced
severe uncontrolled roll oscillations, severe vibration that rendered
the electronic flight instruments partially unreadable, and developed a
high rate of descent. The deicing boots were finally activated and
control of the airplane was regained after a loss of 3,500 feet in
altitude. The report identified causal factors of the incident which
included rapid accumulation of glaze ice that was not evident to the
flightcrew, difficulty of the flightcrew to visually gauge the ice
accretion thickness on the wing's leading edge, and propeller
vibrations that disguised the onset of wing stall. Even though this
incident occurred outside of the United States, and although this
airplane model demonstrated acceptable in-flight icing airworthiness
relative to FAA and Joint Airworthiness Authorities (JAA) requirements,
the incident illustrates the vulnerability of this airplane model to
the safety condition addressed by this AD.
One commenter, British Aerospace, has requested until October 20,
1999, to provide additional data to substantiate that the Model ATP
airplanes and Model HS 748 airplanes can safely operate with ice
accumulations on the protected surfaces. As discussed previously and in
the NPRM, the FAA considers that this same vulnerability exists on all
airplanes equipped with pneumatic deicing boots.
In the interest of safety, the FAA finds that it is not prudent to
delay issuance of the final rules on those airplane models. However,
British Aerospace and any other manufacturer is encouraged to request
approval of an alternative method of compliance with the airworthiness
directive based on substantiating data indicating that a particular
aircraft can safely be operated with the ice that would accumulate on
the protected surfaces prior to activation of the ice protection
system.
6. Request To Withdraw the Proposal for Certain Other Airplanes
Two manufacturers request that the proposals regarding Cessna Model
500, 501, 550, 551, and 560 series airplanes, and British Aerospace
(Jetstream) Model 4101 airplanes be withdrawn. The manufacturers advise
that the testing summarized in their comments provides evidence that
the current procedures provide a safe method to operate those airplane
models. The manufacturers conclude that, based on the service history
and data provided to the FAA, the proposed AFM revision for those
models is unnecessary.
The FAA concurs that the notice of proposed rulemaking for Cessna
Model 500, 501, 550, 551, and 560 series airplanes should be withdrawn
based on the following information. The manufacturer performed a
complete evaluation of the stall and handling characteristics with
simulated ice shapes on the Model 550 (Bravo) series airplanes. Stall
speeds and warning margins were evaluated with a \1/2\-inch glaze ice
shape and with an ice shape associated with the system failure. This
\1/2\-inch ice shape simulated the ice shape prior to deicing boot
activation. Maneuver margin testing consisted of left and right 40-
degree bank turns. Stall characteristics were evaluated with a \1/2\-
inch rime ice shape configuration. Stall characteristic testing
consisted of wings level and 30-degree bank turns. At the conclusion of
the testing it was determined that the airplane had an
[[Page 63618]]
acceptable stall warning margin with ice shapes present. The
manufacturer maintains that Model 500/501, Model 550/551, and Model 550
(Bravo) series airplanes all use a common wing airfoil with some minor
differences in span and wing loading. These aircraft also use a common
tail configuration (airfoil, span, and leading edge sweep).
Additionally, the FAA reviewed the Type Inspection Report (TIR) for
Model 550 (Bravo) series airplane testing and found that ice shapes
were placed on both the protected and unprotected surfaces.
The Model 560 (Ultra) series airplanes underwent an extensive ice
shape stall investigation. This investigation consisted of stall
testing of the baseline airplane and the airplane with the most adverse
simulated intercycle ice shapes. The ice shapes consisted of \1/2\-inch
shapes on the surfaces protected by boots and 3-inch shapes on
unprotected flight surfaces. The stall speeds determined by this
testing were incorporated into the Safeflight Angle of Attack computer
to increase the stall warning margin during flight in icing conditions.
The Model 560 series airplanes angle of attack computer was also
updated to incorporate a normal mode and an ice mode stall warning
system. The changes to the angle of attack computer on Model 560 and
560 (Ultra) series airplanes were proposed by Rules Docket No. 98-NM-
312-AD.
The FAA notes that extensive testing of Model 550 and 560 series
airplanes (in which acceptable stall protection and maneuver margins at
operational speeds were demonstrated with expected ice accretion on the
deicing boot surfaces) indicates that these airplanes can safely
operate with ice accretions associated with the AFM normal operations
procedures of the deicing boots. These attributes demonstrate that
Model 550 and 560 series airplanes satisfactorily address the unsafe
condition addressed by this AD. Since Model 500 series airplanes are
similar to Model 550 series airplanes, the Model 500 series airplanes
also satisfactorily addresss the unsafe condition addressed by this AD.
The FAA also notes that testing of Model 560 series airplanes revealed
problems in the stall warning margin for flight in icing conditions
that were addressed by previously issued airworthiness directives.
The FAA also concurs that the notice of proposed rulemaking for
British Aerospace Jetstream Model 4101 airplanes should be withdrawn
based on the following information. In response to the FAA's October 1,
1998, letter (discussed previously), British Aerospace submitted a
summary of the handling and performance flight test results that were
produced during the original flight in icing certification. This
summary was referenced in their response to the proposed rulemaking.
The commenter volunteered to provide any reports referenced in the
summary. The FAA requested and subsequently received copies of the full
handling and performance flight test results for certification in the
icing conditions specified in Appendix C of part 25 of the Federal
Aviation Regulations (14 CFR 25), and the JAA draft issue of
AMJ25.1419, which was used as guidance for compliance with JAR/FAR
25.1419. The FAA reviewed these reports and guidance material and finds
that the Jetstream 4101 airplane was adequately tested with a variety
of natural ice accretions on both the protected and unprotected
surfaces. Handling and performance flight test was accomplished for the
following:
Normal Operation of the Deicing Boots, \1/2\- to \3/4\-inch of ice
on the protected wing leading edges and up to 3 inches of ice on
unprotected leading edges; Simulated Failure of the Deicing Boots,
approximately 1 to 1\1/2\ inches of ice on all leading edges; Ice
Accreted During the Take-off Phase, a thin rough layer of ice accreted
during the initial take-off phase to 400 feet, prior to operation of
deicing boots.
These ice accretion depths were established to address the
following: Ice accreted during the rest-time of a deicing cycle,
delayed operation or failure of the system, and residual ice
accumulations. The flight testing examined stall speeds, stall warning
margins, stall characteristics, maneuver margins, longitudinal
controllability, flap configuration changes, ability to trim,
susceptibility to tailplane stall, and longitudinal, lateral, and
directional stability. The angles of attack for activation of the stall
warning system and stall identification system (i.e., stick shaker or
stick pusher) are reset to lower values (i.e., higher speeds) for
flight in icing and safe flight speeds (minimum operating speeds)
established accordingly. Affected AFM performance information was
derived for icing conditions based on the higher operating speeds, in
accordance with JAA draft AMJ25.1419.
The Cessna and British Aerospace aircraft models discussed in this
comment have been tested and, where appropriate, changes have been made
to ensure the airplanes are safe for operations with ice accretions on
the protected surfaces. Without this type of testing and
substantiation, the FAA must conclude the aircraft affected by this
final rule may be subject to adverse aerodynamic effects due to ice
accretions on the protected surfaces prior to deicing boot operation.
Other manufacturers may also develop the necessary data to substantiate
that their airplanes are safe with these accretions and request
approval of an alternative method of compliance.
7. Request To Differentiate Between ``Modern'' Boot Systems and
``Older'' Boot Systems
Several commenters request that the difference between the
``older'' boot systems and the ``modern'' boot systems be explained.
These commenters express concern that although both systems are
addressed in the proposal, there may not be a sound technical reason to
apply the requirements of the proposal to both types of boot systems.
The FAA acknowledges that definitions of ``older'' and ``modern''
pneumatic boot systems should be provided. Therefore, for the purposes
of this AD, ``modern'' pneumatic boot systems may be characterized by
short segmented, small diameter tubes, which are operated at relatively
high pressures [18-23 pounds per square inch (psi)] by excess bleed air
that is provided by turbine engines. ``Older'' pneumatic boot systems
may be characterized by long, uninterrupted, large diameter tubes,
which were operated at low pressures by engine driven pneumatic pumps
whose pressure varied with engine revolutions per minute (rpm). This
low pressure coupled with long and large diameter tubes caused early
de-ice systems to have very lengthy inflation and deflation cycles and
dwell times. (Dwell time is the period of time that the boot remains
fully expanded following the completion of the inflation cycle until
the beginning of the deflation cycle.)
8. Request To Withdraw the Proposal For Airplanes with ``Older'' Boots
Two commenters request that the proposed rules applying to
Gulfstream Model G-159 series airplanes and McDonnell Douglas Model DC-
3 and DC-4 series airplanes be withdrawn. Both commenters state that
those airplane models do not meet the common definition of the word
``modern.'' (See Comment #7 of this final rule for a definition of
``modern'' as used in this AD.) One commenter states that the current
AFM specifically directs the flightcrew to wait for \1/4\-inch of ice
before activating the boots. Further, the commenter asserts that the
current procedure was developed during certification and is the basis
for the airplane's approval for flight into
[[Page 63619]]
known icing. Additionally, the commenters assert that the in-service
safety records for more than 40 years indicates that the existing
procedures are appropriate for these airplanes. The commenter concludes
that the proposed AFM revision is in direct opposition to the
certification findings.
The FAA acknowledges that early activation of the ``older''
pneumatic deicing boots may create the hazard of ice bridging on the
``older'' systems. As discussed in Comment #2 previously, ``older''
boots may be susceptible to ice bridging, and the FAA concurs that
requiring the activation of the boots at the first sign of icing may
actually introduce an unsafe condition on those airplanes. In order to
address this issue, the FAA is taking the following steps. First, to
accommodate certain airplane models of the fleet (i.e., Gulfstream
Model G-159 series airplanes and McDonnell Douglas Model DC-3 and DC-4
series airplanes) that may be equipped with the ``older'' pneumatic
deicing boot system, the FAA is considering the issuance of
supplemental NPRM's for those airplane models. The purpose of the
supplemental NPRM's would be to require an inspection to determine
which type of pneumatic deicing boots are installed on the airplanes,
and to require operation of the boots at the first sign of ice
accretion if the airplanes have been retrofitted with ``modern'' boots.
Second, for aircraft with ``older'' pneumatic boots installed, the FAA
will continue to investigate other solutions to the unsafe condition of
reduced handling qualities or controllability of the airplane due to
ice accumulations on the protected surfaces. If other solutions are
identified, the FAA may consider further rulemaking.
9. Request To Revise AFM Change
One commenter requests that the proposal to operate the boots at
the first sign of ice accretion be limited to the holding and approach
phases of flight. The commenter states that the Aviation Rulemaking
Advisory Committee (ARAC) Ice Protection Harmonization Working Group
(IPHWG) completed a comprehensive review of past icing accidents/
incidents. The IPHWG concluded that the only phases of flight that
demonstrate a safety concern are holding patterns and various approach
segments; since these operations are conducted at lower airplane speed,
instability could occur as a result of ice accumulations on the wing
and tail surfaces.
The FAA does not concur that the AFM revision should be limited to
the holding and approach phases of flight. The FAA acknowledges that
the IPHWG is working on a proposed operations rule that may only be
applicable during holding and approach phases of flight. However, the
IPHWG continues to work on the proposed rule and has not reached
technical agreement. Since discussions are ongoing, it would not be
appropriate to assume that the IPHWG positions as presented by the
commenter will necessarily be reflected in the actual published
proposal.
Another commenter, an airplane manufacturer, stated that the AFM
for Model SF340A/SAAB340B/SAAB 2000 series airplanes currently does not
limit the operation of the deicing boots during specific phases of
flight. The commenter requests that the AFM change required by
paragraph (a) of the proposal be revised to limit the applicable phases
of flight where the AFM specifies that deicing boots should not be
used. Specifically, the commenter requests that the language be revised
to read ``Deicing boots must not be used during take-off and landing.''
The FAA partially concurs, and acknowledges that clarification is
necessary. It was the FAA's intent that the boots do not have to be
operated at the first sign of ice accretion during those phases of
flight if there are existing procedures in the AFM that prohibit the
operation of the boots during specific phases of flight. However, the
boots must always be operated at the first sign of ice accretion if, in
accordance with the AFM, it is acceptable to operate the boots during
all phases of flight. Therefore, the FAA has revised paragraph (a) of
the final rule to state, ``Except if the AFM otherwise specifies that
deicing boots should not be used for certain phases of flight (e.g.,
take-off, final approach, and landing), compliance with the following
is required.''
With respect to the request to specify that the deicing boots must
not be used during take-off and landing, it would be desirable to
customize the AFM limitation for specific models of airplanes. This
would allow the AFM to clearly indicate to the flightcrew when the
deicing boots should be deactivated, rather than necessitating that the
flightcrew first determine if there are other portions of the AFM that
indicate that the deicing boots should not be used during specific
phases of flight. Therefore, the FAA encourages requests for approval
of alternative methods of compliance to customize the AFM limitation to
the specific airplane model.
However, the FAA does not concur with the request to revise the
final rule that applies to Saab Model SAAB SF340A/SAAB340B/SAAB 2000
series airplanes since the existing Saab AFM does not indicate that the
deicing boots should not be used during take-off and landing. If the
commenter has data to indicate that the deicing boots should not be
used during those phases of flight, the commenter should take action to
revise the AFM and request approval of an alternative method of
compliance.
10. Request To Revise Instructions on When To Deactivate the Boot
System
One commenter requests that two changes be made to paragraph (a) of
the proposal. The first change would be to specify that the wing and
tail leading edge pneumatic deicing boot system may be deactivated only
after completion of an entire deicing cycle after leaving icing
conditions. The commenter also requests that the proposal be revised to
add related procedures for operating speeds, and that related
procedures for operation of the autopilot (if any) be discontinued only
after the airplane is determined to be clear of ice. The commenter
states that natural ice shedding, melting, or sublimation from the
protected areas will mostly eliminate residual ice.
Regarding the commenter's first request, the FAA concurs. For the
reasons the commenter stated, the FAA has revised paragraph (a) of the
final rule from: ``The wing and tail leading edge pneumatic deicing
boot system may be deactivated only after leaving icing conditions and
after the airplane is determined to be clear of ice;'' to ``The wing
and tail leading edge pneumatic deicing boot system may be deactivated
only after completion of an entire deicing cycle after leaving icing
conditions.''
Regarding the commenter's second request, the FAA considers that,
since the suggested change would alter the actions currently required
by this AD, additional rulemaking would be required. The FAA finds that
to delay this action would be inappropriate in light of the identified
unsafe condition. However, the FAA is considering additional rulemaking
concerning operating speeds during icing conditions.
11. Requests the FAA Consider the Pilot Workload
One commenter states that the proposal would require the pilot to
monitor ice formation and to activate the deicing system almost
constantly. Another commenter suggests that such increase of the
pilot's workload could, of itself, cause an indirect adverse impact on
operational safety. The commenters request that the FAA
[[Page 63620]]
consider the additional pilot workload if the proposal is adopted.
The FAA has previously considered the effects on the pilot of
requiring that the deicing boots be activated at the first sign of ice
formation anywhere on the airplane, or upon annunciation from an ice
detector system. The FAA acknowledges that current procedures
recommending activation of the deicing boots at a specific ice
accretion thickness require the flightcrew to closely monitor the ice
accretion. However, since a number of airplanes affected by this AD are
equipped with deicing boot systems with automatic operating modes,
operating the deicing boots at the first sign of ice accretion in an
appropriate automatic mode will favorably influence flightcrew
workload. For airplanes not equipped with automatic deicing boot
operating modes, periodic operation of the boots can be accomplished
based on time intervals consistent with existing icing conditions. The
FAA considers that periodic operation of the boots is not a greater
workload burden than closely monitoring the ice accretion thickness.
For the reasons stated, the FAA has determined that it is
unnecessary to revise the final rule.
12. Request To Withdraw the Proposal: Provide Training Instead
Several commenters request that the FAA withdraw the proposal and
ensure that appropriate information and training regarding the use of
the boots is provided to pilots. The commenters also suggest that a
testing program be accomplished by industry. The commenters assert that
such training, along with an analysis of the testing program, would
eliminate the need for requiring that the deicing boots be activated in
accordance with the proposal. One commenter also adds that the AFM
should only be changed to add a warning that delayed activation of the
pneumatic boot system may be unsafe. Another commenter adds that the
language of the proposed AFM revision may conflict with current AFM
procedures and could confuse operators.
The FAA does not concur that substituting mandatory training for
issuance of an AD is appropriate in this case. The FAA acknowledges
that, in addition to the issuance of an AD, information specified in
the revision to the AFM should be integrated into the pilot training
syllabus. However, the development and use of advisory materials and
training alone are not adequate to address the unsafe condition. The
only method of ensuring that certain information is available to, and
mandatory for, the pilot is through incorporation of the information
into the Limitations Section of the AFM. The appropriate vehicle for
requiring such revision of the AFM is issuance of an AD. No change is
necessary to the final rule in this regard.
13. Request To Consider Procedures Already in Normal Procedures Section
One commenter requests concurrence that procedures existing in the
Normal Procedures section of the AFM be considered as compliant with
the requirements of the proposed AD.
The FAA does not concur that procedures specified in the Normal
Procedures section of the AFM are an equivalent method of compliance
with the AD. The FAA considers that, since the Limitations section of
the AFM is the only section of the AFM that is mandatory [Sec. 91.9 of
the Federal Aviation Regulations (14 CFR 91.9)], the subject required
revision to the AFM must be included in the Limitations section. No
change is necessary to the final rule in this regard.
14. Request To Limit the AD to Only Those Operations Conducive to Icing
Two commenters request that the AFM limitation specified in
paragraph (a) of the proposal be limited to those conditions where
operations conducive to icing exist. The commenters provide examples of
conditions where operations not conducive to icing may exist such as
Hawaii; the Caribbean; short, low altitude flights in the summer; etc.
One of these commenters states that, ``under the proposal, dispatch
with an inoperative boot would be considered prohibited even though the
deicing would never be needed.''
The FAA does not concur that revision of the AD is necessary in
this regard. Paragraph (a) of the AD specifically states that wing and
tail leading edge pneumatic deicing boot systems must be activated at
the first sign of ice formation anywhere on the aircraft, or upon
annunciation from an ice detector system, whichever occurs first. The
FAA considers that, regardless of what geographic area an airplane may
be flying in or what season of the year it may be, the boot system must
be activated if those specified conditions occur.
Regarding dispatch with an inoperative boot, current Master Minimum
Equipment List (MMEL) procedures prohibit dispatch of the airplane into
known or forecast icing conditions if the deicing boots are
inoperative. In the event that icing conditions are inadvertently
encountered during operation in accordance with MMEL provisions,
procedures exist to instruct the flightcrew to exit the icing
conditions immediately. The FAA considers that those existing
procedures will prevent conflict between the requirements of this AD
and perceived problems regarding dispatch with inoperative boots. No
change is necessary to the final rule in this regard.
15. Request To Consider Differences in Airplanes Systems
One commenter requests that the AFM revision specified in paragraph
(a) of the proposed rule be revised for those airplanes that are
equipped with icing detection systems. Such a revision should read
``activate the wing and tail leading edge pneumatic deicing boot system
upon annunciation from an ice detector,'' rather than ``at the first
sign of ice anywhere on the aircraft, or upon annunciation from an ice
detector system, whichever occurs first.'' The commenter states that,
since the sensor for the ice detection system detects ice buildup at
the boot, it would make sense for airplanes that have an ice detection
system to activate the boot only when ice is detected at the boot by
the ice detection system. The commenter further points out that
activating the boot when ice is not forming on the boot will not remove
the ice formations elsewhere on the airplane, but will simply
deteriorate the condition of the boot and provide no safety benefit.
Additionally, the commenter adds that if the ice detection system were
inoperative for dispatch, it would be appropriate as a Master Minimum
Equipment List (MMEL) condition to activate the boot at the first sign
of icing.
The FAA does not concur that the final rule should be revised to
address procedures specifically for airplanes equipped with icing
detection systems. Visual detection of icing by the flightcrew has been
certificated as the primary means of ice detection. Therefore, the FAA
has determined that, although ice detection systems may alert the
flightcrew to the presence of icing, the flightcrew is still
responsible to monitor the airframe for ice accretion. No change is
necessary to the final rule in this regard. However, in the event a
turbopropeller airplane equipped with pneumatic deicing boots was also
equipped with an ice detection system that was approved as the primary
ice detection system, the operator could request an alternative method
of compliance in accordance with paragraph (b) of the final rule.
[[Page 63621]]
16. Request To Require Additional Operational Procedures
Several commenters propose that the FAA consider that minimum speed
restrictions be used in conjunction with the early activation of the
deicing boots. Some of the commenters specify that these speed
additions be applied during landing approach. One of the commenters
expresses concern that various reports and research indicate that
increasing the angle-of attack with even a small ice formation on the
airfoil can cause large increases in drag and loss of lift. The
commenter contends that control of the angle-of-attack is critical in
maintaining airfoil performance, and concludes that additional
operational procedures must be added.
The FAA concurs that certain operational procedures may be
beneficial when used with early activation of the deicing boots. As a
complement to this AD, the FAA is considering rulemaking regarding
minimum speeds in icing conditions. As mentioned previously, the FAA
encourages manufacturers to present data via a request for approval of
an alternative method of compliance to substantiate that their
airplanes are either capable of flying safely with ice that accumulates
prior to boot activation, or that they are not capable of flying safely
but there are other means to address the unsafe condition. For example,
in the case of Cessna Model 560 series airplanes, the stall warning
margins were modified to ensure the airplane could safely operate with
ice accretions on the protected surfaces. No change is necessary to the
final rule in this regard.
17. Request To Mandate Installation of an Ice Detection System
One commenter suggests that a required installation of a reliable
ice detection system might alleviate the difficulties associated with
flightcrew recognition of airfoil ice accretions. The commenter notes
that, historically, the problem of ice detection has been the ability
of the flightcrew to either identify that the airfoil has ice adhering
to it or accurately determine that a certain thickness of ice exists on
the airfoil prior to activation of the boot system.
The FAA concurs that installation of a reliable ice detection
system would alleviate the difficulties associated with flightcrew
recognition of airfoil ice accretions. This issue is being addressed by
an ARAC working group. Upon receipt of a recommendation from ARAC, the
FAA may consider further rulemaking. In the interim, the FAA is issuing
these airworthiness directives to impose a relatively simple deicing
boot operational change to address the reduced handling qualities or
controllability of the airplane due to ice accumulations on the
protected surfaces. No change is necessary to the final rule in this
regard.
18. Request To Require Action to Reduce Adhesion Characteristics
One commenter requests that action be taken to minimize or reduce
the ice adhesion characteristics of boot material. The commenter
asserts that one reason flightcrews may be seeing large amounts of
residual ice may be that, as the boot ages, the tendency for residual
ice to stick to the boot surface may increase if the adhesion qualities
of the boot materials are not properly maintained. In addition, the
commenter suggests that the use of certain compounds (e.g., ICEX, an
ice-phobic chemical spray) can reduce ice adhesion by substantial
margins.
The FAA does not concur with the commenter's request to require
rulemaking to reduce adhesion characteristics of boot material. The FAA
considers that normal wear and tear on the deicing boot materials is to
be expected, and the adhesion characteristics of the boot increases as
the boot surface degrades over time. Operators have the responsibility
to monitor the performance of the deicing boots installed on their
airplanes, and to perform maintenance as required.
The FAA acknowledges that use of certain ice-phobic chemicals may
provide an additional safety benefit. However, a variety of factors
(e.g., normal wear and tear, ``patching,'' and oxidation of boot
material) exist in varying degrees on individual airplanes. As a
result, the optimum frequency of application will vary during the life
of the boot. The FAA has received no quantitative data to demonstrate
the adequacy of particular amounts of ice phobic chemical sprays or to
provide adequate intervals of application. Therefore, the FAA cannot
establish an appropriate application interval at this time. However, if
additional data becomes available, the FAA may consider further
rulemaking.
19. Request To Consider the Associated Maintenance Procedures and
Increased Costs
Several commenters point out that certain maintenance requirements
should be considered if the proposed AFM revision is required. One
commenter notes that a detailed review of maintenance procedures should
be conducted regarding the deicing boots to ensure that, as the boot
ages, the boot system continues to effectively shed ice.
Several commenters request that the FAA also consider the
additional costs that the proposed AFM revision would require. One
commenter states that the added cycling of the boots will require
additional maintenance. The commenters express concern that the boots
will wear out faster, need to be replaced at an accelerated rate, and
thereby add additional costs.
The FAA acknowledges the concerns of these commenters. The FAA
considered the deicing boot fatigue issues surrounding the proposed AD,
such as the reliability of the deicing boots. Reliability of the
deicing boots is affected by several factors, including: Maintenance
practices; abrasion during dry air, rain, hail, snow, and icing
operations; oxidation; and, fatigue resulting from boot cycling.
However, none of the commenters provided cost estimates for any of
the maintenance costs or replacement costs. The FAA did receive certain
other information from a large operator of two airplane models that
will be affected by this final rule. (One of the airplane models in
that fleet currently observes the early-activation procedures required
by this final rule and the other airplane model does not.) The operator
stated that the largest contributor to periodic replacement of deicing
boots on the fleet was erosion of the boot surface, rather than fatigue
that would be caused by activation of deicing boots at the first sign
of ice accretion.
The FAA recognizes that, in accomplishing the requirements of any
AD, operators may incur ``incidental'' costs in addition to the
``direct'' costs that are reflected in the cost analysis presented in
the AD preamble. However, the cost analysis in AD rulemaking actions
typically does not include incidental costs. In the case of this AD,
for example, the requirements are to revise the AFM to include certain
information. How operators actually ``implement'' that information
thereafter (once it is placed in the AFM) may vary greatly among them:
For some operators, implementation may necessitate extensive retraining
among their flightcrews; for others, implementation may merely be
considered a typical part of the routine, continuous training of their
flightcrews. In light of this, it would be nearly impossible for the
FAA to calculate accurately or to reflect all costs associated with the
AFM revision required by this AD. The FAA has determined that direct
and incidental costs are still outweighed by the safety benefits of the
AD.
[[Page 63622]]
Conclusion
After careful review of the available data, including the comments
noted above, the FAA has determined that air safety and the public
interest require the adoption of the rule with the changes described
previously. The FAA has determined that these changes will neither
increase the economic burden on any operator nor increase the scope of
the AD.
Cost Impact
None of the airplanes affected by this action are on the U.S.
Register. All airplanes included in the applicability of this rule
currently are operated by non-U.S. operators under foreign registry;
therefore, they are not directly affected by this AD action. However,
the FAA considers that this rule is necessary to ensure that the unsafe
condition is addressed in the event that any of these subject airplanes
are imported and placed on the U.S. Register in the future. The FAA
estimates that airplanes of U.S. registry will be affected by this AD.
Should an affected airplane by imported and placed on the U.S.
Register, it will take approximately 1 work hour per airplane to
accomplish the required AFM revisions, at the average labor rate of $60
per work hour. Based on these figures, the cost impact of the AD on
U.S. operators is estimated to be $60 per airplane.
The cost impact figure discussed above is based on assumptions that
no operator has yet accomplished any of the requirements of this AD
action, and that no operator would accomplish those actions in the
future if this AD were not adopted.
Regulatory Impact
The regulations adopted herein will 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 final
rule does not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is
not a ``significant regulatory action'' under Executive Order 12866;
(2) is not a ``significant rule'' under DOT Regulatory Policies and
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action
and it is contained in the Rules Docket. A copy of it may be obtained
from the Rules Docket at the location provided under the caption
ADDRESSES.
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the
Administrator, the Federal Aviation Administration amends part 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:
99-19-13 British Aerospace Regional Aircraft (Formerly British
Aerospace, Aircraft Group): Amendment 39-11302. Docket 99-NM-147-AD.
Applicability: Model HS 748 series airplanes equipped with
pneumatic deicing boots, certificated in any category.
Compliance: Required as indicated, unless accomplished
previously.
To ensure that flightcrews activate the wing and tail pneumatic
deicing boots at the first signs of ice accumulation on the
airplane, accomplish the following:
(a) Within 10 days after the effective date of this AD: Revise
the Limitations Section of the FAA-approved Airplane Flight Manual
(AFM) to include the following requirements for activation of the
ice protection systems. This may be accomplished by inserting a copy
of this AD in the AFM.
Except if the AFM otherwise specifies that deicing
boots should not be used for certain phases of flight (e.g., take-
off, final approach, and landing), compliance with the following is
required.
Wing and Tail Leading Edge Pneumatic Deicing Boot
System, if installed, must be activated:
--At the first sign of ice formation anywhere on the aircraft, or
upon annunciation from an ice detector system, whichever occurs
first; and
--The system must either be continued to be operated in the
automatic cycling mode, if available; or the system must be manually
cycled as needed to minimize the ice accretions on the airframe.
The wing and tail leading edge pneumatic deicing boot
system may be deactivated only after completion of an entire deicing
cycle after leaving icing conditions.
(b) 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, International Branch, ANM-
116, FAA, Transport Airplane Directorate. The request shall be
forwarded through an appropriate FAA Operations Inspector, who may
add comments and then send it to the Manager, International Branch,
ANM-116 ACO.
Note 1: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the International Branch, ANM-116 ACO.
(c) Special flight permits may be issued in accordance with
Secs. 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.
(d) This amendment becomes effective on December 27, 1999.
Issued in Renton, Washington, on November 10, 1999.
John J. Hickey,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 99-30138 Filed 11-19-99; 8:45 am]
BILLING CODE 4910-13-U
