[Federal Register Volume 61, Number 89 (Tuesday, May 7, 1996)]
[Rules and Regulations]
[Pages 20616-20636]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-10728]
[[Page 20615]]
_______________________________________________________________________
Part III
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
14 CFR Part 39
Airworthiness Directives; Final Rules
Federal Register / Vol. 61, No. 89 / Tuesday, May 7, 1996 / Rules and
Regulations
[[Page 20616]]
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 96-CE-01-AD; Amendment 39-9587; AD 96-09-11]
RIN 2120-AA64
Airworthiness Directives; de Havilland, Inc. DHC-6 Series
Airplanes
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment adopts a new airworthiness directive (AD) that
applies to de Havilland DHC-6 series airplanes. This action requires
revising the Airplane Flight Manual (AFM) to provide the flight crew
with recognition cues for, and procedures for exiting from, severe
icing conditions, and to limit or prohibit the use of various flight
control devices. This amendment is prompted by results of a review of
the requirements for certification of the airplane in icing conditions,
new information on the icing environment, and icing data provided
currently to the flight crews. The actions specified by this AD are
intended to minimize the potential hazards associated with operating
the airplane in freezing rain or freezing drizzle conditions by
providing more clearly defined procedures and limitations associated
with such conditions.
EFFECTIVE DATE: June 11, 1996.
ADDRESSES: Information that relates to this AD may be examined at the
Federal Aviation Administration (FAA), Central Region, Office of the
Assistant Chief Counsel, Attention: Rules Docket 96-CE-01-AD, Room
1558, 601 E. 12th Street, Kansas City, Missouri 64106.
FOR FURTHER INFORMATION CONTACT: Mr. John Dow, Aerospace Engineer, FAA,
Small Airplane Directorate, 1201 Walnut, suite 900, Kansas City,
Missouri 64106; telephone (816) 426-6934; facsimile (816) 426-2169.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations (14 CFR part 39) to include an AD that would apply
to de Havilland DHC-6 series airplanes was published in the Federal
Register on January 25, 1996 (61 FR 2175). The action proposed to
require revising the Airplane Flight Manual (AFM) to specify procedures
that would prohibit flight in freezing rain or freezing drizzle
conditions (as determined by certain visual cues), limit or prohibit
the use of various flight control devices, and provide the flight crew
with recognition cues for, and procedures for exiting from, severe
icing conditions.
Disposition of Comments
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
In addition to the proposed rule described previously, in January
1996, the FAA issued 17 other similar proposals that address the
subject unsafe condition on various airplane models (see below for a
listing of all 18 proposed rules). These 17 proposals also were
published in the Federal Register on January 25, 1996. This final rule
contains the FAA's responses to all public comments received for each
of these proposed rules.
----------------------------------------------------------------------------------------------------------------
Docket No. Manufacturer/airplane model Federal Register citation
----------------------------------------------------------------------------------------------------------------
96-CE-01-AD de Havilland DHC-6 Series............... 61 FR 2175
96-CE-02-AD EMBRAER EMB-110P1/EMB-110P2............. 61 FR 2183
96-CE-03-AD Beech 99/200/1900 Series................ 61 FR 2180
96-CE-04-AD Dornier 228 Series...................... 61 FR 2172
96-CE-05-AD Cessna 208/208B......................... 61 FR 2178
96-CE-06-AD Fairchild Aircraft SA226/SA227 Series... 61 FR 2189
96-CE-07-AD Jetstream 3101/3201..................... 61 FR 2186
96-NM-13-AD Jetstream BAe ATP....................... 61 FR 2144
96-NM-14-AD Jetstream 4101.......................... 61 FR 2142
96-NM-15-AD British Aerospace HS 748 Series......... 61 FR 2139
96-NM-16-AD Saab SF340A/SAAB 340B/SAAB 2000 Series.. 61 FR 2169
96-NM-17-AD CASA C-212/CN-235 Series................ 61 FR 2166
96-NM-18-AD Dornier 328-100 Series.................. 61 FR 2157
96-NM-19-AD EMBRAER EMB-120 Series.................. 61 FR 2163
96-NM-20-AD de Havilland DHC-7/DHC-8 Series......... 61 FR 2154
96-NM-21-AD Fokker F27 Mark 100/200/300/400/500/600/ 61 FR 2160
700/050 Series.
96-NM-22-AD Short Brothers SD3-30/SD3-60/SD3-SHERPA 61 FR 2151
Series.
95-NM-146-AD Aerospatiale ATR-42/ATR-72 Series....... 61 FR 2147
----------------------------------------------------------------------------------------------------------------
Comment 1. Support for the Proposals
Numerous commenters support the FAA's intent to minimize the
potential hazards associated with operating airplanes of any type
design in severe icing conditions. One commenter states that the
limitation prohibiting the use of flaps while enroute and during
holding in icing conditions will be a positive contribution to safety.
Additionally, several commenters support the requirement of the
proposed AD for Aerospatiale airplanes for installation of modified
deicing boots on the outer leading edges of the wings. One of these
commenters states that the incorporation of AFM procedures, in addition
to installation of the modified boots, provide a substantial margin of
safety for the Aerospatiale fleet.
Comment 2. Requests Concerning References to ``Freezing Rain/Freezing
Drizzle''
Raytheon requests that references to a class of meteorological
conditions in the limitations described as ``freezing rain or freezing
drizzle'' should be removed from the proposed rules. Raytheon contends
that instructions for the flight crew should be restricted to hazardous
conditions that are defined by the accumulation of ice. The commenter
states that the term ``severe icing'' has a specific meaning as defined
in the Aeronautical Information Manual: ``The rate of accumulation is
such that the icing/anti-icing equipment fails to reduce or control the
hazard. Immediate diversion is necessary.'' The commenter states that,
although freezing rain or freezing drizzle may involve drops larger
than those specified in Appendix C of part 25 (``Airworthiness
Standards: Transport Category Airplanes'') of the Federal Aviation
Regulations (14 CFR part 25), flight into those conditions does not
always result in accumulation
[[Page 20617]]
of ice beyond the capability of the aircraft nor is severe icing always
the result of freezing rain or freezing drizzle. Raytheon concludes
that the limitation specified in paragraph (a)(1) of the proposals
which reads, ``Flight in meteorological conditions described as
freezing rain or freezing drizzle, as determined by the following
visual cues, is prohibited,'' is an inference or conclusion that does
not follow from the premises.
The European Regional Airlines (ERA) Association states that the
proposals define visual cues to be used to identify ``freezing rain''
and ``freezing drizzle,'' but these criteria are inconsistent with the
criteria defined by the International Civil Aviation Organization
(ICAO) and used by weather observers in aviation meteorological support
services. The FAA infers from this remark that ERA requests the use of
ICAO terminology associated with the visual cues.
The FAA concurs partially. The FAA concurs that most of the
references to ``freezing rain/freezing drizzle'' can be removed from
the final rules. The FAA has revised the final rules to replace certain
references to freezing rain and freezing drizzle with the words
``severe icing.'' The FAA finds that since the visual cues contained in
paragraph (a)(1) of these final rules indicate that icing conditions
have exceeded the limits of the ice protection equipment, the use of
the terminology ``severe icing'' is appropriate. As stated by one
commenter, ``severe icing'' is terminology used to describe icing
conditions that exceed the capabilities of the ice protection
equipment. The terminology ``severe icing'' is commonly used and
understood within the aviation community. Additionally, there should be
no confusion over the use of this term in the final rules because the
AFM revisions required by these AD's define the terminology ``severe
icing'' by specifying the visual cues that indicate when the
capabilities of the ice protection equipment have been exceeded.
However, the FAA would consider a request for approval of an
alternative method of compliance to use terminology other than ``severe
icing'' in an AFM, in accordance with the provisions of these AD's,
provided that adequate justification is presented to support such a
request.
Any inconsistencies that may exist between the criteria used by
weather specialists to define ``severe icing'' and the criteria stated
in these final rules are not relevant for these AD's because these AD's
do not require the flight crew to take any action based on information
provided by a weather observer. For these AD's, the flight crew must
only take action if certain visual cues are present on the airplane.
The FAA has determined that reference to freezing rain and freezing
drizzle should not be removed from the text of the ``Caution'' that
appears in paragraph (a)(2) of the proposals. [Note: The ``Caution''
appears as the ``Warning'' in paragraph (a)(1) of the final rules. An
explanation of this change is contained in the disposition of Comment
49 of these final rules.] Reference to freezing rain and freezing
drizzle in that portion of text is made simply to provide a description
of conditions that may result in ice build-up that exceeds the
capabilities of the ice protection system.
Comment 3. Request for Review of ``Severe Icing'' Terminology
One commenter, the Civil Aviation Authority (CAA), which is the
airworthiness authority for the United Kingdom, requests that use of
the terminology ``severe icing'' be reviewed. The CAA does not believe
it is appropriate that this terminology becomes accepted for
supercooled large droplet (SLD) conditions. The CAA indicates that a
common interpretation for ``severe icing'' is that beyond the limit
specified in Appendix C of part 25 of the Federal Aviation Regulations
(14 CFR part 25), which is at or just over the capability of the ice
protection system.
The FAA has reviewed the use of the terminology ``severe icing'' as
related to SLD. The FAA finds that ice resulting from SLD conditions
may not always meet the criterion specified in the common
interpretation of ``severe icing,'' as described by the commenter. The
FAA notes that while SLD conditions may result in the formation of
severe icing, severe icing also may accrue in conditions such as liquid
water content, temperature, or extent of cloud, when those conditions
exceed the limits specified in Appendix C of part 25 of the Federal
Aviation Regulations (14 CFR part 25). As explained previously, most
references to freezing rain and freezing drizzle have been replaced
with the terminology ``severe icing.'' Additionally, the AFM's for the
affected airplanes include a definition of severe icing.
Comment 4. Request To Withdraw the Proposals: Significant Economic
Impact on Operating Community
A number of commenters request that the proposals be withdrawn
because the effect of these proposed AD's will produce a significant
economic impact on the operating community. The commenters indicate
that many flights would need to be canceled in order to make all
reasonable efforts to avoid encounters with freezing rain/freezing
drizzle conditions--i.e., when these conditions are forecast, airplanes
will be prohibited from flight into those conditions. One commenter
remarks that, based on the actual weather in January 1996, nearly 75
percent of its scheduled flights would have been canceled due to
forecast or actual freezing rain or freezing drizzle conditions if the
AD's had been in effect. The commenters do not believe that the FAA has
considered the economic factors affected by the proposed actions, such
as the number of flights lost per day, crew costs, passenger
compensation, misconnected baggage, etc.
If the FAA does not withdraw the proposals, one commenter states
that the prohibition of flight in freezing rain or freezing drizzle, as
specified in paragraph (a)(1) of the proposals, should be revised. The
commenter suggests the following: ``The aircraft should be immediately
flown clear of icing conditions if ice is seen forming on the upper
surface of the wing behind the leading edge deice boots.'' The
commenter believes that the current wording in the proposals would
cause flight crews to cancel or delay departure not only when freezing
rain or freezing drizzle exists, but also when those conditions are
forecast.
The FAA concurs partially. The FAA finds that some misunderstanding
exists among the commenters concerning the intent of these AD's. Many
of the commenters believe that the AD's will prevent affected airplanes
from flight in forecast freezing rain and freezing drizzle. This is not
the case. The FAA agrees that certain language contained in the AD's
must be clarified to reflect its intent. The FAA has evaluated the
wording proposed by one of the commenters and agrees with it in
principal. However, the FAA has determined that the first limitation in
paragraph (a)(1) of the final rules must be revised in order to
accommodate visual cues other than that specified by the commenter, to
incorporate terminology familiar to the flight crew, and to emphasize
that these AD's address only in-flight icing encounters. Additionally,
in order to ensure that appropriate coordination with Air Traffic
Control is accomplished, the FAA has revised the instruction following
the visual cues in paragraph (a)(1), and has moved that instruction to
the end of the first limitation in paragraph (a)(1) of the final rules.
The entire limitation reads as follows: ``During flight, severe icing
conditions
[[Page 20618]]
that exceed those for which the airplane is certificated shall be
determined by the following visual cues. If one or more of these visual
cues exists, immediately request priority handling from Air Traffic
Control to facilitate a route or an altitude change to exit the icing
conditions.'' (Operators should note that, in the final rule for
Aerospatiale airplanes, only one visual cue is specified. That cue
involves ice on the side window of the airplane.)
Several commenters question certain issues related to dispatch of
the airplane in severe icing conditions. One commenter states that the
procedures specified in the proposed AD's fail to address the
conditions that would prohibit takeoff in freezing rain and freezing
drizzle. The commenter believes the visual cues provided in the
proposals would only appear on an airplane during flight. Thus,
allowable conditions for takeoff during times of forecast freezing rain
or freezing drizzle are left to the individual operator's
interpretation. Another commenter believes that the FAA has not
established a basis for prohibiting flight in all reported freezing
drizzle. The commenter contends that takeoff in freezing rain should
always be prevented, but takeoff in freezing drizzle should be possible
after applying appropriate deicing or anti-icing treatments. One
commenter requests that the FAA clarify how the procedures for exiting
freezing rain/freezing drizzle conditions would apply to takeoff and
landing. The commenter states that landing during those conditions
might, in many cases, be the most expeditious method of avoiding a
hazardous condition. Another commenter suggests that the AFM for
Aerospatiale airplanes should be revised to reflect standard dispatch
rules; however, the commenter provides no justification for this
request.
The FAA concurs that visual cues that would prohibit takeoff in
freezing rain or freezing drizzle were not provided because the FAA's
intent is that these AD's address only in-flight icing encounters.
These AD's do not affect any existing regulations or FAA-approved
operating procedures related to takeoff, dispatch, or release of an
airplane in icing conditions. These AD's only prohibit remaining in
icing conditions when certain visual cues are present on the airplane;
these AD's do not prohibit flight into forecast or reported freezing
drizzle. Operators must comply with existing rules that require an
airplane to be free of ice prior to takeoff. Further, the FAA finds no
need to revise the AFM for Aerospatiale airplanes to reflect standard
dispatch rules. The FAA also considers that landing the airplane when
freezing rain/freezing drizzle conditions are encountered would, in
many cases, be the most expeditious method of exiting the conditions.
Such landing would be in compliance with the limitation that requires
the flight crew to exit the severe icing conditions.
Two commenters indicate that the first note that appears in
paragraph (a)(1) of the proposed rules could be interpreted to mean
that if freezing rain or freezing drizzle is forecast anywhere along
the route of flight, the airplane could not be dispatched. One of the
commenters concludes that forecasting methodologies are inadequate and
would need to be improved. The other commenter suggests that the FAA
remove the word ``purely'' from the note. The same commenter requests
that the FAA clarify that the airplane may be dispatched if the
forecast may indicate freezing rain/freezing drizzle conditions.
Another commenter indicates that the wording of the same note is
unclear as to how the FAA defines a ``purely'' inadvertent encounter.
The commenter states that examples of such purely inadvertent
encounters would be helpful.
One commenter asks the following questions in regard to the same
note:
--What are ``reasonable efforts?''
--What does ``immediately exit'' mean? Are the procedures for
immediately exiting listed in the Air Traffic Controller's Handbook or
the Airman's Information Manual? Can a pilot operating the airplane in
a holding pattern decide on his/her own to immediately descend below
the freezing level without regard to other traffic?
One commenter states that the note should be placed in the Normal
Procedures Section of the AFM, rather than in the Limitations Section.
The commenter provides no justification for this request.
The FAA concurs that clarification of this note is necessary. The
FAA originally included the note in the AD's to clarify the intent of
the rules. Since the first instruction and the limitation that follows
have been revised in these final rules, the FAA finds that inclusion of
the clarifying note is no longer necessary. In order to avoid any
possible misinterpretation of the intent of the limitation on flight in
freezing rain or freezing drizzle, the FAA has removed the first note
that appeared in paragraph (a)(1) of the proposals. These AD's do not
prohibit flight into forecast or reported freezing rain or freezing
drizzle. This means that the aircraft is not prohibited from takeoff,
dispatch, or release simply because the forecast may indicate freezing
rain or freezing drizzle, but is prohibited from continued flight in
severe icing conditions.
Comment 5. Request To Withdraw the Proposals: No Unsafe Condition Has
Been Established
Several commenters request that the proposals be withdrawn because
no unsafe condition has been established with respect to airplane
handling characteristics in severe icing conditions. One commenter
states that the preamble of the proposals does not provide data that
establish an unsafe condition; the preamble only indicates that there
are inadequate data to represent all possible conditions. Another
commenter remarks that the FAA's dismissal of the significance of the
test results with the specious comment, ``such airplanes could develop
ice shapes other than those tested,'' is wholly speculative, and is an
invalid basis on which to issue an AD under the provisions of part 39
(``Airworthiness Directives'') of the Federal Aviation Regulations (14
CFR part 39).
The FAA does not concur that these AD's should be withdrawn. As
stated in the preamble to the proposals, the FAA has not required that
airplanes be shown to be capable of operating safely in icing
conditions outside the icing certification envelope specified in
Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part
25). This means that any time an airplane is flown in icing conditions
for which it is not certificated, there is a potential for an unsafe
condition to exist or develop and the flight crew must take steps to
exit those conditions expeditiously. Further, the FAA has determined
that flight crews are not currently provided with adequate information
necessary to determine when an airplane is operating in icing
conditions for which it is not certificated or what action to take when
such conditions are encountered. The absence of this information
presents an unsafe condition because without that information, a pilot
may remain in icing conditions for which the airplane has not been
proven to be safe. These AD's correct the unsafe condition by requiring
AFM revisions that provide the flight crews with visual cues to
determine when icing conditions have been encountered for which the
airplane is not certificated, and by providing procedures to safely
exit those conditions.
Additionally, in the preamble to the proposed rules, the FAA
discussed the investigation of roll control anomalies to explain that
this investigation was not a
[[Page 20619]]
complete certification program. The testing was designed to examine
only the roll handling characteristics of the airplane in certain
droplets the size of freezing drizzle. The testing was not a
certification test to approve the airplane for flight into freezing
drizzle. The results of the tests were not used to determine if these
final rules were required, but rather to determine if design changes
were needed to prevent a catastrophic roll upset. The roll control
testing and the AD's must be viewed as two unrelated actions.
Comment 6. Request To Withdraw the Proposals: Unsafe Condition Is
Outside Certification Limits
One commenter states that the proposed AD's should be withdrawn
because the issuance of AD's to address the problems of icing
encounters outside of the limits for which the airplane is certificated
is a completely inappropriate application of part 39 of the Federal
Aviation Regulations (14 CFR part 39). Another commenter contends that
since the Aerospatiale aircraft passed all present certification
testing, what transpired beyond the limits of certification should not
be held against that aircraft.
The FAA does not concur that the AD's should be withdrawn on the
basis that the unsafe condition is outside the icing certification
envelope. Flight in icing conditions that are outside the icing
certification envelope occurs during the normal service life of an
airplane. Apart from the visual cues provided in these final rules,
there is no existing method provided to the flight crews to identify
when the airplane is in a condition that exceeds the icing
certification envelope. The appropriate vehicle for providing this
method of identification is through issuance of an AD. The FAA
acknowledges that the Aerospatiale airplane has been shown to comply
with existing certification rules; however, no airplane is certificated
for flight in icing conditions outside of Appendix C of part 25 of the
Federal Aviation Regulations (14 CFR part 25).
Comment 7. Request To Withdraw the Proposals: Proposals Unfairly
Discriminate Against Turbopropeller-Powered Aircraft
Several commenters state that the proposed AD's should be withdrawn
because the AD's unfairly discriminate against turbopropeller-powered
aircraft. The commenters contend that by issuing these proposed rules,
the FAA is creating a public perception that turbopropeller-powered
aircraft are less safe than other aircraft.
Numerous commenters oppose the statement contained in the preamble
of the proposals which indicates that since turbopropeller-powered
airplanes are more likely to operate at low altitudes and to make more
frequent landings, they are more likely to encounter icing conditions
that are outside the icing envelope. One commenter states that the mere
fact that turbopropeller-powered airplanes make more frequent landings
is irrelevant for the following reasons:
--Every flight encounters the same atmospheric conditions after takeoff
and prior to landing, whether the airplane is powered by a
turbopropeller or turbojet engine;
--There are numerous airplanes powered by turbojet engines that operate
on segments equal in duration to those operated by many turbopropeller-
powered aircraft; numerous airplanes powered by turbojet engines make
just as frequent landings; and
--Even if turbopropeller-powered aircraft do make more frequent
landings, there is no negative inference to be drawn from that fact;
more opportunities are available to ensure that ice has not formed on
the aircraft if the aircraft lands more frequently.
One commenter states that the altitudes where SLD conditions exist
are the same altitudes at which jets would encounter those conditions
during the departure and arrival phases of flight. Flight in SLD
conditions that would have a negative effect on a turbopropeller-
powered airplane would have the same effect on a jet, since both are
certificated under the same rules with regard to flight into adverse
weather, and both fly at about the same speeds during the departure and
arrival phases of flight. Additionally, another commenter adds that no
airplane, whether it is powered by a turbopropeller, turbojet, or
turbofan engine, is certificated for operation in SLD conditions.
Another commenter indicates that icing encounters take place at
altitudes below the cruising altitudes of most turbopropeller-powered
aircraft used in scheduled service; this also occurs on airplanes
powered by turbojet engines. Icing encounters occur during takeoff,
climb, descent, holding, and landing phases of flight on both types of
aircraft. The commenter adds that operating the airplane in a holding
pattern for a prolonged period in severe icing conditions is hazardous
for both turbojet and turbopropeller-powered aircraft. The commenter
explains that, although the exposure time per flight hour of a long-
haul jet aircraft is less, the exposure on a per flight basis is
exactly the same. The commenter states that, like landing gear life
limits, the proper measure of exposure to freezing rain/freezing
drizzle should be the number of flights, not the number of flight
hours.
Another commenter, Saab, states that Saab Model SAAB 2000 series
airplanes have a unique power-to-weight ratio, which makes it
comparable with airplanes of the same size and, in some relevant areas
such as climb performance and single engine ceiling, even far superior.
Operators of those airplanes can operate the aircraft over-the-weather
at flight level (FL) 310. This means that these Saab airplanes operate
on jet profiles and, therefore, are not exposed to the icing conditions
that are outside the icing envelope any more than the airplanes that
are excluded from the proposals.
The FAA does not concur that the proposals should be withdrawn. The
FAA does not intend to imply through issuance of these AD's that
turbopropeller-powered airplanes are less safe than airplanes having
other types of propulsion systems. As stated in the preamble of the
proposals, the FAA addressed certain airplanes as a higher priority for
two reasons:
--Turbopropeller-powered airplanes are more likely to operate at low
altitudes and to make more frequent landings; therefore, they are more
likely to encounter icing conditions that are outside the icing
envelope specified in Appendix C of part 25 of the Federal Aviation
Regulations (14 CFR part 25); and
--The flight crew of an airplane having an unpowered roll control
system must rely solely on physical strength to counteract roll control
anomalies, whereas a roll control anomaly that occurs on an airplane
having a powered roll control system need not be offset directly by the
flight crew.
Since the issuance of the proposed rules, the FAA has reconsidered
this reasoning. The FAA acknowledges that simply because an airplane is
turbopropeller-powered and has a particular flight profile, that
airplane should not be addressed as a higher priority. However, this
does not diminish the significance of the necessity of the flight crew
of an airplane having an unpowered roll control system to rely on
physical strength to counteract roll control anomalies. The subject
airplanes all have pneumatic deicing boots and unpowered aileron
controls, which have been common denominators in the accident and
incident history
[[Page 20620]]
concerning flight in icing conditions and, in particular, during
conditions when SLD was believed to be present. Therefore, airplanes
having those design features are of immediate concern to the FAA and
were addressed as a higher priority. Additionally, these AD's primarily
address airplanes used in regularly scheduled passenger service in the
United States.
The FAA finds that the comment indicating that more frequent
landings provides more opportunity to verify that ice has not formed is
irrelevant. It also could be said that more frequent landings gives
more opportunity for ice to form. The FAA agrees with the statement
that holding for prolonged periods in severe icing conditions is
hazardous for all aircraft types. The FAA is considering initiating an
assessment of the need to prohibit all aircraft from continued flight
in severe icing conditions as defined in these AD's.
Although Transport Canada Aviation does not request that the
proposed AD's be withdrawn, the commenter indicates that roll control
anomalies could exist for all aircraft whether they have powered or
unpowered roll control systems. Transport Canada Aviation adds that
some jet-powered aircraft have unpowered ailerons.
The FAA concurs that roll anomalies could exist for all aircraft
whether they have powered or unpowered roll control systems. However,
these AD's address airplanes having both deicing boots and unpowered
aileron controls. The FAA acknowledges that other airplanes that have
powered ailerons may be subject to roll problems in severe icing
conditions due to loss of lift. However, the FAA is not aware of a
mechanism that would allow ice to produce an uncommanded control
deflection on airplanes having powered flight control systems. In
addition, airplanes having powered roll control systems do not have
direct feedback of aerodynamic forces to the pilot. However, the FAA is
considering initiating an assessment of the need to apply similar
limitations to other aircraft types.
Comment 8. Request To Withdraw the Proposals: Affected Airplanes Are
Not Same Type Design as Accident Airplane
Several commenters contend that the proposals should be withdrawn
because the FAA has not established clearly that the airplanes
addressed in the proposed rules have the same type design as the
Aerospatiale Model ATR-72 series airplane that was involved in an
accident in October 1994 that occurred in severe icing conditions.
One commenter questions the words ``same type design,'' and asks if
those words refer to high wing, low wing, T-tail, or aircraft of
another type design.
Three commenters provide justification in support of a request that
certain airplanes be exempt from these AD's:
de Havilland Model DHC-7 and DHC-8 series airplanes: De
Havilland states that the airplanes it manufactures share a
conservative aerodynamic design philosophy that yields exceptional low-
speed handling qualities and demonstrated benign handling qualities in
icing conditions. De Havilland adds that two-thirds of the roll control
authority of these airplanes is provided by hydraulically powered roll
spoilers. A second commenter adds that increased testing has been
conducted on these airplanes.
Fokker F27 Mark 100, 200, 300, 400, 500, 600, 700, and 050
series airplanes: Fokker states that the leading edge boots on Fokker
Model F27 series airplanes and Model F27 Mark 050 series airplanes
extend to a chord wise position, 12.5 percent wing chord, which
precludes all but the very largest droplets impinging on the
unprotected surfaces. Fokker adds that since the accident airplane has
unshielded horn balances and the affected Fokker airplanes do not have
these unshielded horn balances, Fokker airplanes will not experience
roll upset problems. Fokker indicates that aerodynamically balancing
the control surfaces by means of unshielded horn balances was not
applied because of the bad service experience of the Vickers Viking
aircraft in 1946.
Beech Model 200 and 200C airplanes: Raytheon states that
these particular airplane models are not normally considered to be
commuter aircraft, and that issuance of an AD would be contrary to the
stated purpose of the proposals because most of these airplanes are
used in non-revenue service. Raytheon states that these airplanes are
all low wing aircraft. Aerospatiale Model ATR-72 series airplanes (the
accident airplane) is 50 percent larger and carries over twice the
number of passengers as these Beech aircraft. For these reasons, as
well as other differences in the geometry of the airplanes (i.e.,
relative aileron span), Raytheon states that the supposition of an
icing hazard in these aircraft is purely speculative.
The FAA does not concur that any of the addressed airplanes should
be exempt from these AD's. The FAA has examined the accident and
incident history in icing conditions and, in particular, those events
believed to involve SLD conditions. Results of this examination
revealed that the type design characteristics that appear to be common
in these events are pneumatic deicing boots and unpowered aileron
controls. Airplanes having those type design characteristics appear to
be more susceptible to control problems in severe icing conditions. In
response to Fokker's remark that its airplanes will not experience roll
control problems since those airplanes do not have unshielded horn
balances, the FAA has determined that horn balances on the accident
airplane were not the source of the uncommanded aileron motion. Design
similarities of the wing, tail, or ailerons do not appear to be a
common denominator among airplanes involved in accidents or incidents
where SLD conditions may have been present.
Saab asks for removal of the sentence that reads, ``Since an unsafe
condition has been identified that is likely to exist or develop on
other airplanes of the same type design * * *.'' Saab states that this
sentence implies that Saab Model SF340A and SAAB 340B series airplanes
have a problem and that this problem is ``likely to develop on other
airplanes of the same type design.'' Yet, there have been no reported
problems on those airplanes, which are not of the same type design as
all other turbopropeller-powered airplanes. Transport Canada Aviation
does not request that the proposals be withdrawn; however, the
commenter requests that the FAA revise the same phrase discussed by
Saab. Transport Canada Aviation requests that the phrase be reworded as
follows: ``Since an unsafe condition has been identified where aircraft
icing certification is not adequate to address the conditions that are
outside of Appendix C of FAR part 25 * * *.''
The FAA does not concur with Saab's request. The FAA acknowledges
that there have been no reported problems involving severe icing
conditions on Saab airplanes. However, Saab Model SF340A and SAAB 340B
series airplanes have pneumatic deicing boots and unpowered aileron
controls, which have been determined to be the common denominators
among the airplanes involved in accidents and incidents in severe icing
conditions. Therefore, the FAA has determined that when severe icing
conditions are encountered on these Saab airplanes, those conditions
must be exited.
Although the FAA has no technical objection to the revised wording
proposed by Transport Canada Aviation, this sentence does not reappear
in the final rules. Therefore, no change to the final rule is
necessary.
[[Page 20621]]
Comment 9. Request for Explanation of the Applicability of the AD's
One commenter requests an explanation of the methodology used by
the FAA to determine that AD's should not be issued for Cessna and
Piper multi-engine aircraft. The commenter also asks if an AD similar
to the proposed rules exists for Boeing Model 737 series airplanes. The
commenter indicates that Model 737 series airplanes have demonstrated
abnormal and unexplained roll tendencies.
The FAA provides the following clarification for this commenter. No
AD's have been issued for Piper airplanes or Boeing Model 737 series
airplanes. However, as reflected in the table above, the FAA has issued
an AD for Cessna Model 208 and 208B airplanes.
Most of the aircraft affected by these final rules are used
primarily in regularly scheduled passenger service in the United
States. However, there are some airplanes affected by the final rules
that are not used in regularly scheduled passenger service. Two of
these are Cessna Model 208 and 208B airplanes. Those airplanes were
included in the final rules because of their accident and incident
history in icing conditions. The FAA is considering an assessment of
the need to prohibit all aircraft from continued flight in severe icing
conditions.
Comment 10. Request To Withdraw the Proposals: Service Experience of
Affected Airplanes Is Satisfactory
Several commenters indicate that the FAA should withdraw the
proposed AD's in light of the satisfactory service experience of the
airplanes addressed in the proposals. The commenters believe that the
FAA is singling out turbopropeller-powered aircraft without any regard
for the operational record of those aircraft.
Several commenters provide justification in support of this
request:
One commenter states that de Havilland airplanes have been
successfully operated for over 30 years without one instance of roll
upset or flight control problems.
De Havilland indicates that de Havilland Model DHC-8
series airplanes have been in service for 11 years and have accumulated
6 million flights and 5 million flight hours without any incidents due
to icing.
De Havilland adds that de Havilland Model DHC-7 series
airplanes have been in service for 18 years and have accumulated 3.7
million flights and 2.7 million flight hours without any incidents due
to icing.
Another commenter has not experienced any icing related
upsets or control irregularities in its fleet of de Havilland Model
DHC-8 series airplanes and Beech Model 1900 series airplanes.
One commenter operates 21 Beech Model 1900D airplanes, 32
EMBRAER Model EMB-120 series airplanes, and 41 Aerospatiale Model ATR-
42 and ATR-72 series airplanes; none of these airplanes have
experienced any icing incidents this season.
One commenter indicates that airplanes produced by Beech,
EMBRAER, and Jetstream Aircraft Limited (JAL) have no record of
uncommanded roll due to asymmetrical build-up of ice on surfaces beyond
the deicing boots.
One commenter notes that it has not experienced any
unusual icing characteristics on its fleet of EMBRAER Model EMB-120
series airplanes and Aerospatiale Model ATR-72 series airplanes.
Fairchild notes that in over 26 years and 15,000,000
flight hours in passenger service, there has never been a reported
incident where the controllability of Fairchild Aircraft SA226 and
SA227 series airplanes were in jeopardy as a result of any icing
encounters (including SLD icing encounters).
The Luftfartsverket (LFV), which is the airworthiness
authority for Sweden, states that no ice build-up behind the wing boots
has ever been reported on Saab Model SF340A, SAAB 340B, or SAAB 2000
series airplanes. Additionally, the leading edge on these airplanes can
be inspected easily during flight.
Saab remarks that no roll anomaly problems in icing
conditions have occurred during the extensive service experience of
Saab Model SF340A and SAAB 340B series airplanes.
The FAA does not concur that the AD's should be withdrawn. The fact
that an airplane has a perfect safety record in icing does not negate
the fact that no airplane has been certificated for flight into SLD.
The FAA has determined that a need exists to provide the flight crew
with useful safety-related information regarding the limitations of the
airplane concerning flight in severe icing conditions. The purpose of
issuing these final rules is to provide the flight crew with such
information.
One commenter, Transport Canada Aviation, requests that the
proposals apply only to those airplanes that have a demonstrated
history of in-service problems as a priority. The commenter states that
the hazards relating to operation in icing conditions exist for all
types of aircraft. (The commenter does not request that the proposed
rules be withdrawn.)
The FAA does not concur with this request. As explained previously,
the FAA has issued AD's for airplanes having pneumatic deicing boots
and unpowered aileron controls as a priority. Airplanes having these
design features are of immediate concern to the FAA because these
features have been common denominators in the accident and incident
history concerning flight in icing conditions and, in particular,
during conditions when SLD was believed to be present. The FAA is
considering the need for rulemaking to impose similar limitations on
other aircraft.
Comment 11. Request To Withdraw the Proposals: Extensive Testing
Revealed No Icing Problems
Several commenters request that the proposals be withdrawn because
extensive testing revealed no icing problems on many different
turbopropeller-powered airplanes, even though those tests likely
exceeded any icing certification tests ever performed on other civil
aircraft types, including large jet-powered transport category
airplanes. Fokker states that Fokker Model F27 series airplanes do not
demonstrate unacceptable roll control characteristics in severe icing
conditions; however, Fokker submits no data to substantiate this
statement.
The FAA does not concur. The FAA finds that successful completion
of the roll upset evaluation is not a valid reason for withdrawing the
AD's. On the contrary, if the evaluation had demonstrated anomalies,
the FAA may have concluded that action beyond that required by these
AD's was necessary to address the demonstrated unsafe condition. The
testing was designed to examine only the roll handling characteristics
of the airplane in certain droplets the size of freezing drizzle to
determine if any design changes are necessary to prevent catastrophic
control surface deflection. The testing was not a certification test to
approve the airplane for flight into freezing drizzle since many of the
components and their functions were not tested (e.g., pitch control,
engine and propeller, performance, stall warning, windshield, air data
sensors and fuel system vents). Further, freezing rain was not tested.
Satisfactory demonstration of those tests does not remove the FAA's
responsibility to provide a safe operating environment for the
passengers and crew.
JAL comments that its airplanes are not subject to the addressed
unsafe condition, and that the FAA had
[[Page 20622]]
concurred with this contention. JAL states that the FAA agreed that, by
the controllability evaluation process, all Jetstream aircraft types
had been demonstrated to be not susceptible to roll control anomalies
in freezing rain or freezing drizzle conditions.
The FAA does not concur with JAL's position concerning its
airplanes. All Jetstream airplanes affected by these AD's successfully
completed the roll upset evaluation. However, as stated previously, no
airplanes were tested in freezing rain conditions. The roll upset
evaluation only addressed conditions that were believed to have existed
during an accident involving a transport category airplane that
occurred in October 1994. Therefore, since no airplane has been tested
in all freezing rain and freezing drizzle conditions, no airplane has
been demonstrated to be safe for continued flight in these conditions.
Comment 12. Request To Withdraw the Proposals: Publish Advisory
Materials and Require Training
Several commenters request that, in lieu of issuing the proposed
rules, the FAA publish appropriate advisory materials and require
training for recognition, avoidance, and exit from severe icing
encounters as part of the required severe weather training for pilots
and dispatchers. Two commenters suggest that the FAA include such
requirements in the operating rules specified in part 121
(``Certification and Operations: Domestic, Flag, and Supplemental Air
Carriers and Commercial Operators of Large Aircraft'') of the Federal
Aviation Regulations (14 CFR part 121). Another commenter indicates
that, since jets and piston-engine aircraft also could develop ice
shapes other than those tested, training should not be provided only to
pilots of turbopropeller-powered airplanes, but to pilots of all
aircraft. Some commenters also suggest that the FAA has successfully
addressed other issues through increased awareness and training
requirements, rather than by issuing AD's against every airplane type
design to require revising the Limitations Section of the AFM. The
commenters cite windshear, ground deicing, and clear air turbulence as
examples of such issues. The commenters contend that, except where
configuration changes are needed, such as in the case of windshear
detection devices, improved awareness and training programs--not AD's--
have been highly effective in achieving needed safety improvements.
The FAA does not concur. The FAA considers that substituting
advisory material and mandatory training for issuance of an AD is not
appropriate, nor would this adequately address the unsafe condition.
The FAA fully supports the development of advisory materials and
training. Part 121 (``Certification and Operations: Domestic, Flag, and
Supplemental Air Carriers and Commercial Operators of Large Aircraft'')
and part 135 (``Air Taxi Operators and Commercial Operators'') of the
Federal Aviation Regulations (14 CFR parts 121 and 135) require that
appropriate training concerning limitations such as those contained in
these AD's be incorporated into air carriers' training programs.
However, the FAA's position is that the development and use of such
advisory materials and training alone are not adequate to address the
subject unsafe condition. Currently, the AFM's specify that the
affected airplanes are certificated for flight in icing conditions;
however, the AFM's do not specify a method of determining whether the
certification limits for those conditions have been exceeded.
Consequently, the FAA finds that these AFM's must be revised to provide
limitations for flight in icing conditions and to provide the flight
crew with a method of determining when those limitations have been
exceeded.
The FAA does not concur that amending part 121 of the Federal
Aviation Regulations (14 CFR part 121) in lieu of issuing these AD's is
appropriate. The FAA's position is that the appropriate place to inform
the flight crew of the limitations of the airplane is in the AFM. The
appropriate vehicle for mandating such AFM revisions is through
issuance of an AD. In addition, an AD will ensure that the
incorporation of such AFM revisions is not left to each operator's
individual discretion and that flight crews receive pertinent
information. The FAA may consider an assessment of the need to provide
training to pilots of all aircraft types for flight in severe icing
conditions.
The commenters reference windshear as an example of an issue that
was handled successfully without issuance of an AD to revise the AFM's.
In this case, the AFM's for all airplanes having an onboard windshear
system were revised to provide the flight crew with procedures for
responding when the system gives an alert. Although no AD was issued to
mandate these AFM revisions, without revising the AFM, operators could
not comply with the section of part 121 of the Federal Aviation
Regulations (14 CFR part 121) that requires installation of the
windshear detection devices. In conclusion, although AFM revisions were
not required by an AD, AFM changes were mandated indirectly by a new
part 121 regulation.
The commenters also reference ground deicing. Part 91 (``General
Operating and Flight Rules'') of the Federal Aviation Regulations (14
CFR part 91) prohibits takeoff of an airplane unless the airframe is
clear of ice; therefore, there is no need to provide additional
limitations concerning the amount of ice that would be acceptable for
takeoff. However, in the case of severe icing conditions addressed by
these final rules, the AFM's currently allow flight in icing, but the
AFM does not define when the limits of the certificated icing operation
envelope have been exceeded.
Concerning the issue of clear air turbulence, issuance of an AD was
not required because an airspeed limitation associated with turbulent
air penetration was already in the AFM's. Therefore, in this case, the
issue was addressed in the AFM as well as through awareness and
training.
Comment 13. Request To Withdraw the Proposals: Incorporate Operational
Issues Into a Training Curriculum
Two commenters request that the proposals be withdrawn because the
proposed AD's address an operational issue that should be incorporated
into an operator's training curriculum. One commenter states that
pilots must be made aware of the hazards of icing and that extended
operation of an airplane in any icing encounter that results in
significant airframe accretion of ice is unacceptable.
The FAA does not concur that the AD's should be withdrawn based on
the commenters' request. The FAA acknowledges that these AD's address
an operational issue. When the requirements of these AD's are
accomplished and the AFM limitations are revised, this material will be
incorporated necessarily, as explained previously, into the training
curriculum for the flight crews and dispatchers, if applicable, in the
operator's approved training program. In this manner, pilots and
dispatchers, if applicable, will be informed of the hazards of icing
and that continued operation of an airplane in certain icing conditions
is prohibited.
Comment 14. Request To Withdraw the Proposals: Require Training for Air
Traffic Controllers and Weather Specialists
Two commenters request that the FAA implement additional policy to
require training for air traffic controllers and weather specialists in
the
[[Page 20623]]
recognition, avoidance, and procedures to exit severe icing conditions.
The FAA does not concur that these AD's should be withdrawn.
However, the FAA acknowledges that implementation of these AD's may
necessitate additional training beyond that which is already required
for air traffic controllers and weather specialists. The FAA may
consider the need to provide training concerning recognition,
avoidance, and procedures for exiting severe icing conditions. However,
the intent of these AD's is to provide the flight crew with recognition
cues for, and procedures for exiting from, severe icing conditions. The
appropriate vehicle for requiring that such information be included in
the AFM's is through issuance of an AD.
Comment 15. Request To Withdraw the Proposals: Add a Caution to the AFM
One commenter requests that, in lieu of issuing the proposed AD's,
a ``Caution'' should be added to the AFM to inform pilots to exit icing
conditions if ice was observed to be forming aft of the protected
surfaces of the wings. The commenter states that information regarding
the use of flaps and the autopilot in icing conditions could also be
incorporated into the AFM. The commenter does not indicate which
section of the AFM should include this material.
The FAA does not concur. The FAA finds that the requirement to exit
severe icing conditions and information concerning use of the autopilot
during flight in those conditions must be included in the Limitations
Section of the AFM. Additionally, information concerning use of the
flaps during those conditions should be included in the Procedures
Section of the AFM. The appropriate vehicle for requiring these changes
to the AFM is through issuance of an AD.
Comment 16. Request To Withdraw the Proposals: Require Alternative AFM
Limitation
One commenter requests that, in lieu of an AD, the FAA require an
alternative AFM limitation that reads as follows: ``This aircraft is
certified for flight into icing conditions as specified by Appendix C
of Part 25. Actual icing encountered may be greater than Appendix C
requirements.''
The FAA does not concur. The suggested limitation does not provide
guidance as to how a pilot can identify and safely exit icing
conditions that have exceeded those specified in the icing envelope in
Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part
25). These AD's are intended to provide the flight crew with visual
cues which indicate that icing conditions have exceeded the
capabilities of the ice protection equipment, and with procedures to
safely exit those conditions. No change to the AD's is necessary.
Comment 17. Request To Withdraw the Proposals: AFM Revisions Already
Are Required
One commenter requests that the proposals be withdrawn because
section 121.133 (``Manual Requirements: `Preparation' '') of the
Federal Aviation Regulations (14 CFR 121.133) already requires that
operators incorporate revisions into the AFM's; therefore, issuance of
the proposed AD's is unnecessary.
The FAA does not concur. Section 121.133 of the Federal Aviation
Regulations (14 CFR 121.133) does not specifically require that AFM's
be updated to current revisions. Section 121.141 (``Airplane or
Rotorcraft Flight Manual'') of the Federal Aviation Regulations (14 CFR
121.141) requires that the current AFM be carried on the aircraft, but
does not require incorporation of the most current revisions.
Additionally, the commenter does not address the need to change the
AFM's for airplanes that operate under parts 135 (``Air Taxi Operators
and Commercial Operators'') and 91 (``General Operating and Flight
Rules'') of the Federal Aviation Regulations (14 CFR parts 135 and 91).
The appropriate vehicle for ensuring that the Limitations Section of
the AFM's is changed is through issuance of an AD.
Comment 18. Request To Withdraw the Proposals: Use Existing AFM
Revisions
The General Aviation Manufacturers Association (GAMA), on behalf of
its members, states that some of the affected manufacturers have
prepared FAA-approved revisions for the AFM's for their products. GAMA
indicates that those revisions incorporate specific information
regarding cues for recognizing severe icing conditions and procedures
for exiting such conditions, if encountered. Therefore, if the proposed
AD's are adopted, the requirements of the AD's would supersede the
information operators have already incorporated into the AFM's with
less appropriate information that is not type design specific.
One commenter, JAL, requests that certain existing AFM revisions
for the affected Jetstream airplanes be cited in the proposed AD's for
those airplanes in lieu of the content of the proposed AD's. (However,
JAL does not request that the proposals be withdrawn for this
particular reason.) JAL indicates that the existing AFM revisions have
already been FAA-approved.
The FAA does not concur with the commenters' requests. The FAA
acknowledges that the AFM revisions required by these final rules will
supersede previously approved AFM revisions. However, the FAA is
unaware of any AFM that addresses all of the provisions specified in
these final rules, nor of any AFM that contains specific visual cues
that the FAA has not included in the final rules. Even if AFM material
currently exists that does contain all of the provisions of the final
rules, the FAA finds that issuance of an AD would still be necessary to
mandate the provisions of the AFM revisions. However, the FAA would
consider a request for approval of an alternative method of compliance,
in accordance with the provisions of this AD, for those operators
having AFM's that already contain all of the provisions of the final
rules.
Another commenter requests that the FAA withdraw the proposal that
applies to Fairchild Model SA226 and SA227 series airplanes. The
commenter states that the AFM for those airplanes currently contains
visual cues to aid the flight crew in recognition of weather conditions
conducive to SLD. This AFM also provides procedures for avoidance of
such conditions. The commenter adds that these AFM procedures result in
additional operating limitations on the aircraft with regard to severe
weather conditions. The commenter believes these AFM procedures address
all current FAA requirements.
The FAA does not concur that the AFM for Fairchild Model SA226 and
SA227 series airplanes addresses all of the proposed requirements of
the proposed rule. For example, the Limitations section of the AFM for
those airplanes does not require the flight crew to exit severe icing
conditions. For this reason, the FAA does not consider the AFM for
Fairchild Model SA226 and SA227 series airplanes to be equivalent to
the information specified in these AD's.
Comment 19. Request To Withdraw the Proposals: Develop Rulemaking To
Address Airplane Certification Outside of Appendix C
Three commenters suggest that instead of arbitrarily prohibiting
operation of the airplane, the FAA should undertake a well-designed
research program and, if warranted, devise a rulemaking plan for
certification of airplanes outside of Appendix C of part 25 of the
Federal
[[Page 20624]]
Aviation Regulations (14 CFR part 25). One commenter also suggests
possible retroactive implementation of a new Appendix C.
The FAA does not concur because of the length of time that would be
required to implement the commenters' suggestion. The FAA finds that
action is required prior to the commencement of the next icing season
to prohibit the continued flight of airplanes in icing conditions that
have been shown to be unsafe and for which the airplanes have not been
certificated. However, the FAA is currently considering initiating an
assessment of the need to revise Appendix C and the possibility of its
retroactive implementation.
Transport Canada Aviation states that the FAA has determined that
there may be a problem with the certification requirements for icing on
de Havilland Model DHC-6, DHC-7, and DHC-8 series airplanes, but not
the specific approval or design features of those airplanes. However,
the commenter does not specifically request that the proposals be
withdrawn.
The FAA does not concur with the commenter's statement. The FAA has
only determined that no adequate means exists for the flight crew to
determine when the icing certification limits have been exceeded. The
purpose of these AD's is to provide more clearly defined procedures and
limitations associated with severe icing conditions. This does not
imply that the certification requirements for icing are inadequate.
Comment 20. Request To Withdraw the Proposals: Issue a ``General AD''
for All Airplane Types
One commenter requests that a ``general AD'' be issued to prohibit
all airplane types from inadvertent flight into hazardous SLD
conditions. Another commenter adds that if encounters with freezing
rain/freezing drizzle conditions must be reported to Air Traffic
Control, such reporting also should apply to flight crews of all
airplane types.
The FAA does not concur with the commenter's request. For the
reasons discussed earlier in the preamble of this AD, the FAA has
determined that airplanes having pneumatic deicing boots and unpowered
aileron controls are of immediate concern and have been addressed as a
higher priority. The FAA finds that action is required prior to the
commencement of the next icing season to prohibit the operation of
these airplanes in icing conditions that have been shown to be unsafe
and for which the airplanes have not been certificated. However, the
FAA is currently considering initiating an assessment of the potential
adverse effects of SLD on all airplane types.
Comment 21. Request To Withdraw the Proposals: Establish a Detailed
Reporting System
One commenter requests that the FAA establish a detailed reporting
system for inadvertent encounters with severe SLD. The commenter
envisions a system that would provide a database for better
identification of controllability issues and visual indications related
to these encounters.
The FAA does not concur with the commenter's request. The FAA has
been advised that the Regional Airline Association (RAA) has already
established an ``Unusual Icing Reporting Program'' for the purpose
described by the commenter; therefore, establishing another reporting
program would duplicate this benefit.
Comment 22. Request To Withdraw the Proposals: Revise the Master
Minimum Equipment List (MMEL)
Two commenters request that, instead of addressing an MMEL item in
an AD [i.e., the icing detection lights referenced in paragraph (a)(1)
of the proposals], the FAA should require that the MMEL be revised. A
third commenter adds that the decision to change the MMEL should be
made by FAA Operations Inspectors based on local conditions. One
commenter states that the prohibition of dispatch with any inoperative
ice detection lights would preclude any efforts by an operator to
enhance safety by installing a second set of bulbs. The commenter adds
that under this proposed rule, this type of action would be penalized
by simply doubling the chances of a burned out bulb grounding the
aircraft. In practice, if one were to add a fully redundant set of
bulbs, it would enhance safety by allowing the equivalent of the
current illumination level even with a bulb burned out.
The FAA does not concur with these requests. FAA Operations
Inspectors are not authorized to make MMEL revisions. The FAA has
determined that it is prudent to address the icing detection lights in
these final rules to ensure uniform and immediate application of the
requirements of the AD's. Concerning the example provided by one of the
commenters, if an operator chooses to add a fully redundant set of
bulbs, that operator should request approval of an alternative method
of compliance in accordance with the provisions of this final rule.
Although Transport Canada Aviation does not request that the
proposals be withdrawn, it requests a revision to the requirement that
all icing detection lights must be operative. For de Havilland Model
DHC-7 and DHC-8 series airplanes, the commenter requests that the
requirement be changed to mandate that at least one outboard and one
inboard inspection light be operative prior to flight into known or
forecast icing conditions at night. Since the MMEL contains a provision
that a suitable lamp/light of adequate capacity be available, this is
considered acceptable in conjunction with other indications of freezing
rain or freezing drizzle. Similarly, for de Havilland DHC-6 series
airplanes, the requirement should be revised to require a suitable
lamp/light for dispatch at night with one wing inspection light
inoperative.
The FAA does not concur. The FAA has determined that the
justification provided by the commenter is not adequate to enable the
FAA to determine if the proposed changes are acceptable. During severe
icing conditions, the flight crew's workload may be high, and there may
be no opportunity to use the portable lamp/light, which, in itself, may
create disorientation in the cockpit due to adverse reflections from
the glass. The FAA's intent in having all inspection lights be
operative at night is to provide the flight crew the best possible
visibility of the airframe. However, the FAA would consider a request
for approval of an alternative method of compliance, in accordance with
the provisions of these AD's, provided that adequate justification is
presented to support such a request.
Comment 23. Request To Withdraw the Proposals: Certify Airplanes for
Flight in Conditions Outside Appendix C
One commenter implies that the airplanes affected by the proposed
rules must be rectified to a level beyond the present certification
requirements for flight in icing.
The FAA does not concur. The final rules do not require
certification of the airplane beyond the current certification
requirements for flight in icing specified in Appendix C. These AD's
simply provide the flight crew with visual cues which indicate that
icing conditions have exceeded the capabilities of the ice protection
equipment, and with procedures to safely exit those conditions.
One commenter requests that the proposal for de Havilland DHC-6
series airplanes be withdrawn because this airplane model is type
certificated in Canada, which is a country with a higher standard than
the United States for operating in icing conditions.
[[Page 20625]]
The FAA does not concur. This commenter did not submit data to the
FAA to substantiate that the airplane has been shown to be safe for
flight outside the icing certification envelope specified in Appendix
C. Additionally, the FAA is unaware of any foreign civil aviation
authority having certification requirements for icing conditions that
are outside of the icing certification envelope used in the United
States.
Comment 24. Request To Withdraw the Proposals: Proposals Prohibit
Takeoff or Approach in ``Light Freezing Drizzle'' Conditions
One commenter requests the proposals be withdrawn because the
proposed limitation would prohibit takeoff or approach when ``light
freezing drizzle'' conditions that are caused by light precipitation
falling through a thin layer of cold surface air below warmer air above
are reported on the surface. The commenter maintains that with
accomplishment of the appropriate ground deicing precautions prior to
takeoff, no hazard to the operation of the airplane is posed.
The FAA does not concur that the AD's should be withdrawn for this
reason. These AD's do not affect any existing regulations or FAA-
approved operating procedures related to takeoff, dispatch, or release
of an airplane in icing conditions, nor do these AD's prohibit
operation in specific meteorological conditions. These AD's only
prohibit remaining in icing conditions when certain visual cues are
present on the airplane. Operators must comply with existing rules that
require an airplane to be free of ice prior to takeoff. Therefore,
takeoff in ``light freezing drizzle'' would only be prohibited by
existing regulations or FAA-approved operating procedures, not by these
AD's. As explained previously, the FAA considers that landing the
airplane when freezing rain/freezing drizzle conditions are encountered
would, in many cases, be the most expeditious method of exiting the
conditions. Such landing would be in compliance with the limitation
that requires the flight crew to exit the severe icing conditions.
Comment 25. Request To Withdraw the Proposals: Proposals Leave
Unanswered Questions
One commenter contends that the proposals leave unanswered
questions. The commenter alleges that without the answers to those
questions, affected parties are deprived of the ability to provide
informed comments and, thereby, are ``denied their rights under the
Administrative Procedures Act (APA) to comment on the proposed rules.''
Specifically, the commenter asks:
--What is unusual icing?
--Does the pilot, Air Traffic Control, dispatch, or the FAA determine
when the conditions exist?
--What is splatter effect?
--Where are the operating instructions incorporated--in the AFM,
training manuals, or some other document?
The FAA infers from the commenter's remarks that the commenter requests
the proposed AD's be withdrawn because informed comments could not be
provided.
The FAA does not concur that the AD's should be withdrawn on this
basis. The FAA does not agree that the public has been deprived of the
ability to provide informed comments, as required by the APA. In
general, the APA requires that notice of the terms or substance of a
proposed rule be published in the Federal Register. The purpose of this
requirement is to ensure that federal agencies thoroughly consider all
information and opinions submitted by the public before any
requirements are imposed. Notice is intended to improve both the
quality of the regulations and their acceptability to the public. The
FAA finds that none of the questions raised by the commenter identify
areas in which the commenter has not been provided a reasonable
opportunity to comment. The fact that the commenter raises questions
suggests that the commenter considers a need for further clarification.
Even if the commenter is correct in that these questions require
clarification, that fact in itself is a comment that can be addressed
properly by simply clarifying terms. The fact that clarification is
necessary does not mean that the public has been denied reasonable
opportunity to comment.
In response to the commenter's questions, the FAA provides the
following clarification. The term ``unusual icing'' did not appear in
the proposed rules. However, the phrase ``unusually extensive ice'' is
referenced in paragraph (a)(1) of the final rules. [This reference
appears in paragraph (a)(2) of the final rule for Aerospatiale
airplanes.] ``Unusually extensive ice'' accrued on the airframe in
areas not normally observed to collect ice is a visual cue that is
subject to interpretation by the flight crew; therefore, a specific
definition of ``unusually extensive ice'' cannot be provided.
These AD's address changes to AFM limitations, which pertain to the
pilot since the pilot is responsible to look for the visual cues
defined in the AD's. Therefore, the pilot determines when severe icing
conditions exist.
The terminology ``splatter effect'' did not appear in the proposed
rules. The FAA infers from the commenter's question that the commenter
is referencing terminology used in paragraph (a)(2) of the proposed
AD's. ``Droplets that splash or splatter on impact at temperatures
below +5 degrees Celsius OAT'' is a visual cue that was included in the
proposed AD's as a method of identifying severe icing conditions.
Concerning incorporation of operating instructions, these final
rules specify that the AFM's be revised. The AD's do not specify that
any other manuals or documents be revised. However, information that is
included in the AFM as a limitation is necessarily included in the
training program.
Comment 26. Request To Clarify Scope of Icing Conditions Addressed
Transport Canada Aviation suggests that the proposals, which
address only freezing rain/freezing drizzle conditions, are not
adequate to cover all hazards related to operation of aircraft in icing
conditions. The commenter makes no specific request.
The FAA concurs that these AD's do not address all icing related
hazards. The FAA's intent is to minimize the potential hazards
associated with operating the airplane in severe icing conditions by
providing the flight crews with more clearly defined procedures and
limitations associated with such conditions. However, no change to the
final rules is necessary.
Comment 27. Request To Expand the Applicability of the AD's
One commenter, the CAA, suggests that the ``coverage'' of the
proposals should be stated clearly. The CAA believes that a restriction
to those operations in ``regularly scheduled passenger service'' is not
warranted for a safety issue as it does not cover cargo, charter, or
private operations. The commenter does not specify which airplane
models should be addressed. The FAA infers from the commenter's remarks
that it requests that the proposed AD's be applicable to other airplane
models that are used in cargo, charter, or private operations that may
have been excluded from the applicability of these AD's.
The FAA does not concur that the applicability of these AD's should
be expanded to include additional airplane models used primarily in
cargo, charter, or private operation. The FAA is currently considering
the need for
[[Page 20626]]
additional rulemaking to address other airplane models having pneumatic
deicing boots and unpowered aileron controls that are used in these
types of service that were not addressed by these AD's. Additionally,
the applicability of these final rules indicates that the AD's apply to
``all'' of the airplane models identified, certificated in any
category. This means that the AD's apply to all of the affected
airplanes, regardless of how those airplanes are operated (including
passenger service, cargo, charter, or private operation).
Comment 28. Request for Design Changes to the Airplanes
One commenter requests that the FAA require design changes to the
airplanes, which, when accomplished, will allow elimination of the AFM
limitations. The commenter states that abnormal roll control anomalies
could be eliminated by design changes that prevent any ice shapes from
forming by using supplemental ice protection added to existing
pneumatic boots or other ice protection installations. The commenter
concludes that, given this added protection, restricting flight in
freezing drizzle could be reduced to allow exposure to these
atmospheric conditions for a reasonable time and would not require
immediately exiting these conditions when encountered as presently
stipulated.
The FAA does not concur that it should require design changes to
airplanes in these AD's. Currently, the FAA is unaware of any design
changes that would allow elimination or reduction of the AFM
limitations specified in these AD's. However, if such design changes
are developed, approved, and become available, the FAA would consider
additional rulemaking to require such changes. The FAA finds that even
if the ice protection system prevented the formation of ice shapes in
front of the ailerons when the airframe is exposed to certain freezing
drizzle conditions, other meteorological conditions still exist (e.g.,
freezing rain) for which the airplane would not be certificated.
Comment 29. Request for More Specific Visual Cues
One commenter requests that the FAA provide more specific visual
cues for identification of freezing rain or freezing drizzle
conditions. The commenter states that the generic visual cues provided
in the proposed AD's are not adequate for aircraft types that
frequently operate in and encounter SLD conditions. For example, ice
could be forming on the upper wing and not the lower wing; therefore,
looking at the lower wing would not be a reliable visual cue. Two
commenters suggest that specific visual cues be provided for each
airplane model. One of these commenters states that subjective cues may
be of limited benefit if the pilot's experience with icing is
inadequate. The other commenter adds that subjective visual cues will
result in varying interpretations (i.e., some unnecessary course
changes in altitudes or service interruptions caused by overly
conservative interpretations). Transport Canada Aviation does not
request more specific visual cues; but states that ``unusually
extensive ice,'' ``normally observed,'' and ``farther back than
normally observed'' are all variable terms that are largely dependent
on flight crew experience. The commenter contends that limitations and
procedures described using these terms will not be consistently
interpreted. In addition, Transport Canada Aviation states that ice on
the lower wing surface aft of the protected area, by itself, is
unlikely to cause a hazard. Moreover, the presence or absence of such
ice cannot be used as an indication of any hazardous accumulation on
the upper wing surface or on the horizontal stabilizer.
The FAA does not concur with the commenters' request to provide
more specific (or airplane-specific) visual cues. The FAA agrees with
the commenters' assertion that, under certain circumstances,
examination of the undersurface of a high wing may not be reliable. The
FAA also agrees that other cues, such as unusually extensive ice
accrued on the airframe in areas not normally observed to collect ice
and accumulation of ice on the propeller spinner farther aft then
normally observed, are subjective and that reliance on pilot judgment
and experience is necessary in such cases. Additionally, the FAA fully
supports the development and use of airplane-specific cues by operators
and manufacturers. Unfortunately, no commenter provided airplane-
specific cues during this comment period.
In summary, the FAA finds that the combined use of the generic cues
provided and the effect of the final rules in increasing the awareness
of pilots concerning the hazard of operating outside of the
certification icing envelope will provide an acceptable level of
safety. However, for those operators that elect to identify airplane-
specific visual cues, the FAA would consider a request for approval of
an alternative method of compliance, in accordance with the provisions
of this AD.
Transport Canada Aviation states that the term ``protected area''
may not be readily recognizable by the flight crew; for example, not
all of a deicing boot surface is ``protected area.'' [This terminology
appears in the second visual cue (in the proposals for airplanes other
than Aerospatiale airplanes) and in the autopilot limitation in
paragraph (a)(1) of the proposals. For Aerospatiale airplanes, this
terminology appears in the secondary indications in paragraph (a)(1) of
the proposal.] The FAA infers that the commenter requests that more
specific language than ``protected area'' be used.
The FAA does not concur that this terminology should be revised.
The FAA considers that a pilot understands that a portion of the
deicing boot would be considered to be unprotected. Therefore, no
additional clarification or definition of the term ``protected area''
is necessary.
Comment 30. Request To Reference Clear Icing Conditions and Clear
Component of Mixed Icing Conditions
One commenter also asks that all references to freezing rain and
freezing drizzle environments and visual cue identification reference
clear icing conditions and the clear component of mixed icing
conditions. According to the commenter, mixed icing conditions can
contain areas of freezing rain and/or freezing drizzle. The commenter
notes that mixed icing has taken on two different definitions within
the aviation community--the ``engineering'' definition (which is
defined in an FAA icing handbook) and the definition pilots use (which
includes areas of clear and rime ice). The commenter states that a
clear definition of these conditions is needed. The commenter adds that
only pilot reports can show that freezing rain/freezing drizzle exists
because forecasting of these conditions is inadequate. The commenter
indicates that while the Aerospatiale airplanes have side window cues
that will accurately identify freezing rain or freezing drizzle, pilots
of other airplanes without such a sophisticated cue may erroneously
report mixed icing.
The FAA does not concur. The FAA acknowledges that freezing rain
and freezing drizzle may be reported as clear/mixed icing conditions.
However, the flight crew must exit icing conditions that produce the
visual cues specified in the final rules. Exiting the icing conditions
is not dependent upon the terminology used to describe the conditions.
Therefore, the FAA has determined that it is not necessary to include
references to clear icing
[[Page 20627]]
conditions and the clear component of mixed icing conditions. In
addition, the FAA has determined that including a discussion in these
AD's of the phenomenon of mixed icing conditions as it relates to the
current state-of-the-art weather forecasting would be premature because
no clear definition of this phenomenon has been agreed upon among the
aviation community. The FAA is currently considering an assessment
during which various icing-related subjects, including mixed icing
conditions, would be addressed.
Comment 31. Request for Research and Use of Wing-Mounted Ice Detectors
One commenter requests that wing-mounted ice detectors, which
provide real-time icing severity information (or immediate feedback) to
flight crews, continue to be researched and used throughout the fleet.
The FAA infers from this commenter's request that the commenter asks
that installation of these ice detectors be mandated by the FAA.
While the FAA supports the development of such ice detectors, the
FAA does not concur that installation of these ice detectors should be
required. The specifications for automatic detectors having the
capabilities to differentiate among freezing rain, freezing drizzle,
and other icing conditions have not been determined. However, if such
ice detectors are developed, approved, and become available, the FAA
may consider further rulemaking action to require installation of such
equipment.
Comment 32. Request to Limit the Applicability of the AD's
One commenter requests that the applicability of the proposals be
limited to airplanes having NACA 430xx airfoils. The commenter asserts
that the unusual pressure peak on the NACA 430xx airfoils at 9 percent
chord caused the ice ridge to form at that point, which resulted in the
accident involving a Aerospatiale Model ATR-72 series airplane. The
commenter states that ``the accident was caused by the poorly designed,
unusual, and fortunately rarely used NACA 430xx airfoils used on this
airplane.''
The FAA does not concur with the commenter's request to limit the
applicability of the AD's. First, the National Transportation Safety
Board (NTSB) has not yet made an official finding of the probable cause
of the accident referenced by the commenter. Therefore, the FAA cannot
assume that airplanes having NACA 430xx airfoils are more susceptible
to the addressed unsafe condition than those airplanes that do not have
this type of airfoil. Second, the FAA has examined the data submitted
by the commenter, and disagrees with the commenter's assertion
concerning the formation of ice ridges. The formation of ice ridges
depends on many factors. Ice ridges have been observed to form in areas
where there is no pressure (commonly, ``suction'') peak. However, the
impingement location of large droplets is more relevant to the
development of ice ridges than the particular pressure distribution.
The commenter does not address the fact that, regardless of the type of
airfoil on an airplane, a substantial sharp edge protuberance in the
vicinity of the suction peak can have adverse consequences to the
aerodynamic performance of the airfoil. Regardless of the cause of
location of ice formations, prevention or removal of the ice is
certainly an acceptable remedy for such conditions, should those
conditions occur. For example, Aerospatiale extended the deicing boots
to prevent the formation of adverse ice ridges.
Comment 33. Request for Approval of Improved Deicing Equipment for
Aerospatiale Airplanes
ATR requests that paragraph (b) of the proposed rule for
Aerospatiale airplanes be revised to indicate that installation of any
improved version of deicing equipment that is approved by the FAA is
acceptable for compliance with the requirements of that paragraph. The
commenter provides no justification for its request.
The FAA does not concur with the commenter's request to revise the
AD. However, if an improved version of deicing equipment is developed,
approved, and available, the FAA would consider a request for approval
of an alternative method of compliance, in accordance with the
provisions of the AD.
Comment 34. Request for Re-Evaluation of Modified Deicing Boots on
Aerospatiale Airplanes
In response to the proposal for Aerospatiale airplanes, one
commenter requests that the new, enlarged deicing boots that are
required to be installed on these airplanes must be re-evaluated before
total confidence in the modified boots is warranted. The commenter
asserts that no test data exist to show that the modified boots will
preclude the problem of large droplets outside of Appendix C. The area
of exposure outside of Appendix C is essentially open-ended, and only
limited testing within a narrow range of droplet diameters was
conducted. Additionally, the test conditions that existed during the
tanker testing conducted at Edwards Air Force Base, which was intended
to be a ``before modification/after modification'' validation program,
were not identical. The commenter adds that no modification will ensure
that any airplane is safe while flying in icing conditions outside
those specified in Appendix C.
The FAA does not concur with the commenter's request for a re-
evaluation of the modified deicing boots. The modified deicing boots
for these airplanes were subjected to an extensive certification
program by both the FAA and the Direction Generale de l'Aviation Civile
(DGAC), which is the airworthiness authority for France. FAA approval
of the modified boots was based on engineering analyses, wind tunnel
testing, flight testing in natural icing conditions, and a validation
program involving a United States Air Force icing tanker. This testing
verified that the modified boots continue to perform the intended
function within the Appendix C icing envelope. In addition, the
extended deicing boots were shown to adequately protect the airplane
from the larger, supercooled water droplets that are believed to have
existed in the area at the time of the accident in October 1994.
It should be noted, however, that it is not intended that the
modified boots provide protection in all possible icing conditions,
including freezing rain/freezing drizzle. However, the FAA considers
that the combination of the enlarged deicing boots, the AFM operational
procedures and restrictions, and the visual cues which indicate entry
into freezing rain/freezing drizzle conditions provides for an enhanced
level of safety during inadvertent flight in these conditions.
Comment 35. Request for Formal Weather Forecasting System for Freezing
Rain/Freezing Drizzle
One commenter supports a requirement to establish a formal system
to provide forecasts of freezing rain/freezing drizzle conditions, as
proposed in paragraphs (b) and (c) of the original proposed rule for
Aerospatiale airplanes. [This proposed requirement was removed from the
subsequent supplemental notice of proposed rulemaking (NPRM) issued for
these airplanes in January 1996.] The commenter states that such a
requirement should remain in effect until forecasting tools are
developed or detection methods are established to prevent dispatch or
operations in conditions outside those specified in Appendix C. The
commenter states that
[[Page 20628]]
the efficacy of the deicing boots has not been shown completely nor
documented; therefore, avoidance of freezing rain/freezing drizzle is
paramount to safety of flight.
The FAA does not concur that such a requirement is necessary. The
FAA agrees that such a system would enhance the safety of flight
operations. However, there is no evidence that lack of a system with
such specialized features would lead to an unsafe condition. Forecasts
of freezing rain/freezing drizzle are a normal part of pre-flight
weather briefings. The FAA is aware, however, of serious limitations
for such a system to provide accurate and timely forecasts of these
conditions during flight in areas that are removed from weather
reporting stations. Quite often, the only indication of the existence
of severe icing conditions is from pilot reports or other direct
observations.
Research is underway currently in industry and the academic
community to address shortcomings in the forecasting of severe icing
conditions. The FAA may consider further rulemaking if advancements in
weather forecasting provide for a reliable method to predict the
occurrence of freezing rain/freezing drizzle conditions during flight
or in areas removed from direct observations.
Comment 36. Request To Approve Earlier Service Bulletin Revisions
One commenter to the proposed rule for Aerospatiale airplanes
requests that the proposed AD be revised to specify that earlier
revisions of service bulletins are acceptable for compliance with the
requirements of the proposed rule. The commenter makes this request so
as to eliminate the need to apply for approval of alternative methods
of compliance when accomplishing service bulletin revisions other than
those specified in the proposed rule.
The FAA does not concur that earlier revisions of the referenced
service bulletins should be cited in the final rule for Aerospatiale
airplanes. However, the FAA would consider a request for approval of an
alternative method of compliance, in accordance with the provisions of
the AD, provided that adequate justification is presented to support
such a request.
Additionally, the FAA has revised the revision levels specified for
certain service bulletins because those revision levels were omitted
inadvertently from paragraph (b) of the proposed rule for Aerospatiale
airplanes. That final rule has been revised to indicate that certain
modifications are to be accomplished in accordance with Revision 1 of
Aerospatiale Service Bulletins ATR42-57-0043, ATR72-57-1015, and ATR72-
57-1016. The correct date for Revision 1 of those service bulletins
(April 10, 1995) was specified in the proposal for the affected
airplanes.
Comment 37. Request To Revise Referenced Service Bulletins
One commenter to the proposal for Aerospatiale airplanes suggests
that service bulletin revisions should contain a statement indicating
that the revision has no effect on previously modified airplanes. The
commenter provides no justification for this request.
The FAA acknowledges that many service bulletins do contain the
suggested phrase as an aid to operators that may already have
accomplished an earlier service bulletin revision. In fact, if a
particular service bulletin is specified in an AD and that service
bulletin is revised, the FAA routinely determines whether the service
bulletin revision adequately addresses the unsafe condition specified
in the AD; if necessary, the FAA amends the AD to cite the later
service bulletin revision.
Comment 38. Request To Revise Visual Cue: Ice on Side Window
One commenter suggests revised wording for the first visual cue
specified in paragraph (a)(1) of the proposed rule for Aerospatiale
airplanes, as follows: ``Freezing rain and freezing drizzle are
characterized by ice covering all or a substantial part of the unheated
portion of either forward side window and/or water splashing or
streaming on the windshield or the side window when in freezing or near
freezing temperatures.'' The commenter states that the present wording
implies that ice will always appear on the side window; however, this
is not the case.
The FAA does not concur with the commenter's request. The
commenter's revised wording suggests that water splashing or streaming
on the windshield or the side window would be a primary cue used to
determine when severe icing conditions are present. The FAA does not
concur that water splashing or streaming on the windshield or the side
window would be a reliable cue in itself. However, this cue may be used
as a supplemental cue to the primary cue of ice accruing on the side
window. No change to the final rule for Aerospatiale airplanes is
necessary.
Comment 39. Request To Remove Visual Cue: Unusually Extensive Ice
Accretion
One commenter, Saab, requests that if the FAA does not withdraw the
proposed AD's, paragraph (a)(1) of the proposal for Saab SF340A and
SAAB 340B series airplanes should be revised. The commenter suggests
that the first visual cue that appears in that paragraph, which relates
to unusually extensive ice accretion, be removed from the proposal for
those airplanes. Saab indicates that critical ice is believed to be ice
that builds up beyond the protected surfaces on the wing. On Saab Model
SF340A and SAAB 340B series airplanes, the pilot has a good view of the
outer wing and the propeller spinner. Unusually extensive ice in other
areas may or may not be significant in determining whether freezing
rain or freezing drizzle is present; however, the primary visual cue
for these airplanes is ice on the spinner/outer wing.
In light of Saab's remarks, the FAA concurs that the visual cue
addressed by the commenter should be removed from the final rule for
Saab Model SF340A and SAAB 340B series airplanes. (That visual cue
remains in place for Saab Model SAAB 2000 series airplanes.) Paragraph
(a)(1) of that final rule has been revised accordingly.
A second commenter, Raytheon, requests that the same visual cue be
removed from the proposal for Beech airplanes. Raytheon indicates that
it does not believe that observation of this visual cue indicates that
the airplane has exceeded the Appendix C icing envelope with respect to
Beech airplanes. Therefore, the cue specified in the proposal would be
irrelevant in an AFM for these airplanes.
The FAA does not concur with Raytheon's request. The commenter has
not submitted data to warrant removal of the visual cue. No change to
the final rule for Beech airplanes has been made.
Comment 40. Request To Remove Visual Cue: Accumulation of Ice on Wing
Surfaces
JAL requests that the FAA remove the generic information contained
in the visual cue concerning accumulation of ice on the wing surfaces
from the proposals for Jetstream airplanes. JAL indicates that, for its
airplanes, the appropriate visual cue is the accretion of ice behind
the protected area of the wing upper surface (not the wing lower
surface).
The FAA concurs partially. The FAA does not agree that the visual
cue should be removed from the final rules for Jetstream airplanes.
However, the FAA finds that this particular visual cue should be
airplane-specific. Therefore, the FAA has customized paragraph (a)(1)
of the final rules for all affected airplanes to specify whether
accumulation of ice is observed on the
[[Page 20629]]
upper or lower surface of the wing, depending upon whether the airplane
is a high- or low-wing airplane. [Operators should note that, for
Aerospatiale airplanes, the cue was customized in paragraph (a)(2) of
the final rule.]
Comment 41. Request To Revise Visual Cue: Accumulation of Ice on
Propeller Spinner
One commenter requests that the FAA revise the visual cue
concerning accumulation of ice on the propeller spinner, as specified
in paragraph (a)(1) of the proposals. For consistency, the commenter
requests that the word ``back'' be replaced with ``aft.''
The FAA concurs with the commenter's request. The final rules have
been revised to change the visual cue to read as follows:
``Accumulation of ice on the propeller spinner farther aft than
normally observed.'' [Operators should note that, for Aerospatiale
airplanes, this change appears in paragraph (a)(2) of the final rule.]
Comment 42. Request To Remove Visual Cue: Accumulation of Ice on
Propeller Spinner
One commenter, JAL, requests that the FAA remove the visual cue
concerning accumulation of ice on the propeller spinner from the
proposals for Jetstream airplanes. JAL indicates that on Jetstream
Model ATP airplanes and Model 748 series airplanes, the propeller
spinner is not visible from the flight deck. On Jetstream Models 3101,
3201, and 4101 airplanes, the propeller spinner is visible from the
flight deck, but flight test experience indicates that there is no
unique correlation between the extent of spinner ice accretion and the
existence of freezing rain/freezing drizzle conditions.
The FAA concurs partially. The FAA concurs that since the propeller
spinner is not visible from the flight deck on Jetstream Model ATP
airplanes and Model 748 series airplanes, the visual cue can be removed
from paragraph (a)(1) of the final rules for these models. The FAA does
not concur that this visual cue should be removed from the AD's for
Jetstream Models 3101, 3201, and 4101 airplanes. The commenter did not
submit data to substantiate its assertion that flight test experience
indicates there is no unique correlation between the extent of spinner
ice accretion and the existence of freezing rain/freezing drizzle
conditions. Therefore, it is uncertain if the commenter's flight test
airplane was equipped with instrumentation that would allow the
detection and/or measurement of droplets outside the Appendix C
conditions, and if the airplane had flown into icing conditions
containing freezing rain or freezing drizzle.
Comment 43. Request To Remove Limitation to Immediately Exit Freezing
Rain/Freezing Drizzle
Saab requests that the FAA remove a sentence from paragraph (a)(1)
of the proposals that requires the pilot to immediately exit freezing
rain or freezing drizzle conditions by changing altitude or course.
This commenter points out that the first limitation contained in the
proposal for Saab airplanes (``Flight in meteorological conditions
described as freezing rain or freezing drizzle, as determined by the
following visual cues, is prohibited . . .'') already prohibits flight
in these conditions, and the pilot should respond accordingly. Raytheon
believes a conflict exists between using observations of ice accretion,
as required by paragraph (a)(1) of the proposed rules, and the
``determination'' of certain meteorological conditions.
The FAA concurs partially. The FAA does not agree that the sentence
discussed by Saab should be removed from paragraph (a)(1) of the final
rules. As explained previously, the first limitation in paragraph
(a)(1) of the final rules has been revised to read: ``During flight,
severe icing conditions that exceed those for which the airplane is
certificated shall be determined by the following visual cues. If one
or more of these visual cues exist, immediately request priority
handling from Air Traffic Control to facilitate a route or an altitude
change to exit the icing conditions.'' (This wording is slightly
different in the final rule for Aerospatiale airplanes because only one
visual cue is provided.) The FAA finds that this revision to the final
rules addresses the commenters' concerns with regard to the proposed
limitations.
One commenter poses various questions concerning the last sentence
of the first instruction listed in the procedures for exiting the
freezing rain/freezing drizzle environment in paragraph (a)(2) of the
proposals. (That sentence reads as follows: ``Asking for priority to
leave the area is fully justified under these conditions.'')
--What does the term ``priority'' provide a pilot when asking for
priority to leave icing conditions?
--What if there were three simultaneous requests for ``priority?''
--What Air Traffic Control procedures exist for treating an immediate
request for ``priority?''
--Where is the term ``priority'' defined?
The commenter states that confusion over terms that have not been
defined clearly by the FAA has partially resulted in accidents and
incidents. However, the commenter does not cite a specific case in
which this occurred.
The FAA has re-examined the last sentence of the first instruction
listed in the procedures for exiting the freezing rain/freezing drizzle
environment in paragraph (a)(2) of the proposals. The FAA has
reconsidered use of the term ``priority.'' The FAA finds that more
appropriate language that would be understood clearly by the flight
crew and Air Traffic Controllers should be used in that instruction.
Existing training for flight crews and Air Traffic Controllers
addresses priority handling of airplanes. However, the FAA will issue
additional information for Air Traffic Controllers to further clarify
priority handling of airplanes in severe icing conditions. The FAA
finds that the limitations specified in paragraph (a)(1) of the final
rules will result in the pilot taking appropriate steps to exit the
icing conditions. Therefore, the FAA finds that the sentence questioned
by the commenter may be removed from the final rules without affecting
safety. Accordingly, the FAA has removed that sentence from the final
rules.
Additionally, in order to use terminology in the procedures for
exiting the severe icing environment that is consistent with the
terminology used in the revised limitation and to simplify certain
language, the FAA has revised the first instruction of the procedures.
The revised instruction reads as follows: ``Immediately request
priority handling from Air Traffic Control to facilitate a route or an
altitude change to exit the icing conditions in order to avoid extended
exposure to flight conditions more severe than those for which the
airplane has been certificated.''
Comment 44. Request To Change the Note Concerning the Autopilot
One commenter, ATR, requests that the FAA revise the second note in
paragraph (a)(1) of the proposal for Aerospatiale airplanes. As
proposed, ATR believes the last sentence of the note is too
restrictive. ATR proposes the following: ``The autopilot may mask
tactile cues . . . characteristics. Therefore, when any ice is visible
on the airplane, the pilot should consider flying manually for short
periods in order to check the absence of any anomaly.''
Two commenters request that the FAA remove a similar note
concerning the autopilot from the proposals for airplanes other than
Aerospatiale
[[Page 20630]]
models. One of the commenters, JAL, states that the note contains
advisory information and should not appear in the Limitations Section
of an AFM.
The FAA concurs with ATR's comment that the last sentence of the
note is too restrictive; that sentence has been removed from the final
rules for all airplanes. However, the FAA does not agree with JAL's
contention that the explanation of the relationship between the
autopilot and the masking of tactile cues is inappropriate for
insertion in the Limitations Section of an AFM. On the contrary, the
FAA finds that inclusion of such information will increase the level of
understanding and, consequently, will increase the level of safety.
In light of this, the FAA finds that the note may be removed from
paragraph (a)(1) of the final rules for all airplanes; however, the
information contained in the first sentence of that note has been
combined with the autopilot limitation in paragraph (a)(1) of the final
rules. The final rules have been revised accordingly.
Comment 45. Requests To Remove Autopilot Limitation
Saab requests that the FAA revise the second limitation that
appears in paragraph (a)(1) of the proposal for Saab airplanes. As
proposed, this limitation indicates that use of the autopilot is
prohibited when any ice is observed forming aft of the protected
surfaces of the wing, or when unusual lateral trim requirements or
autopilot trim warnings are encountered. Saab asks that this autopilot
limitation be modified to take into consideration the autopilot system
design on these airplanes, which provides out-of-trim warnings;
therefore, the autopilot can be used up to the point where a warning is
triggered. Saab adds that the triggering point is early enough for the
warning to be taken, should the reason be ice build-up beyond the
protected surfaces. Additionally, there is no automatic disconnect if
the autopilot servo reaches its limit torque, which would prevent any
surprise to the pilot during an out-of-trim condition.
Another commenter, EMBRAER, requests that use of the autopilot not
be limited for EMBRAER Model EMB-120 series airplanes. The commenter
states that flight tests have demonstrated the safe ability of these
airplanes to depart a freezing rain/freezing drizzle condition with the
autopilot on.
Raytheon also objects to the autopilot limitation. Raytheon
suggests that a better approach is to inform the pilots of the nature
of ice accretion, and then let the pilots decide when to use the
autopilot. The commenter believes that prohibiting use of the autopilot
when any ice is observed aft of the protected surfaces of the wing is a
rigid requirement that takes away a valuable aid to the flight crew
when it may be needed most. Raytheon states that there is no evidence
that the autopilots on Beech aircraft would mask an icing related
control problem. The commenter points out that tests on those aircraft
disclosed no icing related control problem to mask. The commenter adds
that trying to anticipate every situation with an absolute prohibition
may lead to other unsafe conditions.
The FAA does not concur that the autopilot limitation should be
modified or removed from the AD's for any of the affected airplanes.
The limited amount of time the pilot is using manual controls instead
of the autopilot would not result in an unsafe condition. In normal
operational environments and conditions, the autopilot is a valuable
aid that reduces the workload of the flight crew. However, under
abnormal conditions (ice aft of the protected surfaces, unusual lateral
trim, or autopilot trim warnings), the autopilot will mask the build-up
of large or unusual control forces in one or more axes. Therefore, for
the short period of time necessary to exit severe icing conditions, the
safest course of action would be manual pilot control. Even if an
autopilot does not automatically disconnect, the pilot may choose to
disconnect the autopilot and could then be faced unexpectedly with
unusual control forces. These reasons also still hold true with
airplanes that have been flight tested with the ice shapes.
Since the issuance of the proposed rules, the FAA has re-examined
the autopilot limitation specified in paragraph (a)(1) of the
proposals. The FAA recognizes that clarification is necessary with
regard to its intent concerning that limitation. That limitation, as
specified in the proposals, states that use of the autopilot is
prohibited when any ice is observed forming aft of the protected
surfaces of the wing, or when unusual lateral trim requirements or
autopilot trim warnings are encountered. However, the FAA's intent
concerning that limitation is that the autopilot be disconnected when
the flight crew observes any of the visual cues identified in paragraph
(a)(1) of the AD's. The need to disconnect the autopilot arises when an
amount of ice accumulates that indicates the limits of the ice
protection equipment have been exceeded, regardless of the means by
which the flight crew becomes aware of the accumulation of ice.
Additionally, the FAA acknowledges that the autopilot limitation,
as proposed, could be misinterpreted to mean that the autopilot must be
disengaged when unusual lateral trim or autopilot trim warnings are
encountered, regardless of whether the airplane is in icing conditions.
However, the FAA only intended that the autopilot limitation apply
while the airplane is in icing conditions.
In light of this, the FAA has determined that the autopilot
limitation contained in paragraph (a)(1) of the final rules must be
revised. The FAA has changed that limitation to read as follows:
``Since the autopilot may mask tactile cues that indicate adverse
changes in handling characteristics, use of the autopilot is prohibited
when any of the visual cues specified above exist, or when unusual
lateral trim requirements or autopilot trim warnings are encountered
while the airplane is in icing conditions.'' (This wording is slightly
different in the final rule for Aerospatiale airplanes because only one
visual cue is provided.) This revision more accurately reflects the
FAA's intent and is, therefore, a logical outgrowth of the proposed
rules.
Comment 46. Request To Insert Procedures in Limitations or Abnormal
Procedures Section of AFM
One commenter suggests that operations in icing conditions that
exceed the capability of the airplane should be described in the
Limitations or Abnormal Procedures Section of the AFM, rather than in
the Normal Procedures Section, as specified in paragraph (a)(2) of the
proposals.
The FAA concurs partially. The FAA agrees that the Abnormal
Procedures Section may be an appropriate location for the procedures
for exiting severe icing conditions. However, the FAA does not agree
that such operational procedures should appear in the Limitations
Section of the AFM since such procedures are not limitations.
Additionally, upon further review, the FAA finds that AFM's may have
neither an Abnormal Procedures nor a Normal Procedures Section.
Consequently, to provide operators with flexibility as to where the
procedures specified in paragraph (a)(2) should be incorporated in the
AFM, that paragraph has been revised to require that the ``Procedures''
Section of the AFM be revised. This means that the procedures may be
inserted in the ``Normal Procedures,'' ``Abnormal Procedures,'' or
other ``Procedures'' Section of the AFM, as appropriate.
[[Page 20631]]
Comment 47. Request To Remove Duplicate Visual Cues
Two commenters indicate that certain visual cues specified in
paragraph (a)(2) of the proposals are duplicated in the ``Warning''
that is also contained in that paragraph. One commenter states that the
duplication of text reduces the impact of the message. Another
commenter questions whether the visual cues and procedures for exiting
the icing environment are intended to be part of the AFM material. The
FAA infers from these remarks that the commenters request that
duplicate text be removed.
Transport Canada Aviation requests that the ``Warning'' be removed
because indications of the possible hazard are progressive and may not
necessarily require immediate action from the pilot. The commenter
suggests that renaming this as a ``Caution'' may be more appropriate.
The FAA concurs partially. The FAA agrees that duplicate text
should be removed from the ``Warning'' section that appeared in the
proposals. The FAA finds that only one unique instruction appears in
the ``Warning'' in paragraph (a)(2) of the proposals: ``If the flaps
are extended, do not retract them until the airframe is clear of ice.''
Therefore, the FAA has added that instruction to the procedures for
exiting the severe icing environment in paragraph (a)(2) of the AD's.
The remainder of the ``Warning'' section that appeared in the proposals
has been removed from the final rules.
Comment 48. Request for Revision to Instruction for Flaps Extension
Saab requests that the FAA revise an instruction contained in the
procedures for exiting the freezing rain/freezing drizzle environment
in paragraph (a)(2) of the proposals. That instruction indicates to
``Avoid extending flaps during extended operation in icing conditions *
* *.'' Saab suggests the following: ``Do not extend flaps when holding
in conditions where ice is accreting on the airframe.'' Further, the
commenter asks that this instruction be inserted as a ``caution'' in
the Limitations Section of the AFM, rather than into the Normal
Procedures Section, as specified in the proposed rule. Saab believes
that it is imperative that the flaps not be extended in such cases.
Inserting the instruction into the Limitations Section, rather than the
Normal Procedures Section, would add strength to the requirement.
Another commenter states that this same instruction appears to be
in conflict with previously approved AFM revisions which state,
``Sustained flight in icing conditions is prohibited with flaps
extended.'' However, the commenter does not provide a suggestion for
rewording this instruction.
The FAA concurs that the procedures related to extension of the
flaps can be reworded somewhat. For clarification purposes, the FAA has
replaced the word ``avoid'' with ``do not'' in that procedure in
paragraph (a)(2) of the final rules. This revision eliminates the
conflict discussed by the second commenter. However, the FAA does not
agree that revising the remainder of the instruction, as suggested by
Saab, provides any additional clarification.
The FAA agrees that inserting the revised wording in the
Limitations Section of the AFM, rather than in the Normal Procedures
Section, would be acceptable; however, this would expand the scope of
the originally proposed rules and would necessitate reopening the
comment period to provide additional opportunity for public comment. In
light of the time required to complete the rulemaking process in
advance of the upcoming icing season and in consideration of the safety
issues addressed by these final rules, the FAA finds that the AD's
should be issued without additional delay. However, the FAA would
consider a request for approval of an alternative method of compliance,
in accordance with the provisions of this AD, to include this
information in the Limitations Section of an operator's AFM.
Transport Canada Aviation requests that this instruction be revised
to read as follows: ``Do not extend flaps during operation in icing
conditions, except for approach and landing. Operation with flaps
extended will result in a reduced wing angle-of-attack with the
possibility of ice forming on the upper surface further aft on the wing
than normal, possibly aft of the protected area.''
The FAA concurs partially. The FAA does not concur with the
commenter's suggested rewording to limit use of the flaps in all
operation in icing conditions except approach and landing. The wording
proposed in the AD's would affect use of the flaps only during extended
operation in icing conditions. The FAA finds that an amount of ice
sufficient to cause control problems is more likely to accumulate
during prolonged operations in icing conditions. Further, the FAA does
not concur that the words ``operation of the flaps can result in a
reduced angle-of-attack * * *'' should be changed to ``operation of the
flaps will result in a reduced angle-of-attack * * *'' in this
instruction. Operation with flaps extended does not always result in a
reduced angle-of-attack. For instance, during extension of the flaps
while the airplane is slowing, the angle-of-attack will increase.
The FAA concurs with the suggestion to include the words ``the
possibility of ice forming on the upper surface further aft * * *'' The
FAA acknowledges that under certain conditions the droplets will not
impinge further aft with a reduced angle-of-attack. The final rules
have been revised to add the words suggested by the commenter to the
sixth instruction specified in the procedures for exiting the severe
icing environment contained in paragraph (a)(2) of the AD's. That
revised instruction reads as follows: ``Do not extend flaps * * * with
the possibility of ice forming on the upper surface * * *''
Comment 49. Requests To Revise ``Caution'' Paragraph
One commenter asks that the heading, ``Caution,'' which appears in
paragraph (a)(2) of the proposals, be renamed ``Warning'' because this
section is intended to prevent loss of life or injury. Transport Canada
Aviation requests that the ``Caution'' section be changed to a note.
The commenter provides no justification.
The FAA concurs partially. The FAA does not concur that the
``Caution'' should be changed to a note because this section is
intended to prevent loss of life or injury. In light of this, the FAA
concurs with the commenter's request to rename the ``Caution'' section
``Warning.'' The FAA finds that ``Warning'' is a stronger term and
would be a more appropriate heading for the paragraph in question.
Additionally, the FAA finds that the ``Warning'' provides advisory
information that should precede the first limitation in paragraph
(a)(1) of the AD's. Accordingly, the FAA has revised the heading
``Caution'' to ``Warning'' in the final rules. In addition, the
``Warning'' has been placed at the beginning of paragraph (a)(1) of the
final rules. The FAA has determined that including this information in
the Limitations Section of the AFM will not impose an additional burden
on any operator, since it is informational only and does not
necessitate providing an additional opportunity for public comment.
Additionally, the commenter notes that an undefined term,
``extreme,'' is used in a sentence in the ``Caution'' paragraph of the
proposals, as follows: ``Flight in freezing rain, freezing drizzle, or
mixed icing conditions (supercooled liquid water and ice crystals) may
result in extreme ice build-up on protected surfaces * * *'' The FAA
infers from
[[Page 20632]]
this remark that the commenter asks that the word ``extreme'' be
removed from the ``Caution'' paragraph.
The FAA concurs. The FAA finds that removing the word ``extreme''
would not change the intent of the sentence and may eliminate
confusion. The word ``extreme'' has been removed from this section of
the final rule. In addition, for clarification purposes, the FAA has
revised the first sentence of the proposed ``Caution'' from ``Severe
icing comprises environmental conditions * * *'' to ``Severe icing may
result from environmental conditions * * *''
Comment 50. Request To Remove Visual Cues: Identification of Freezing
Rain/Freezing Drizzle
One commenter indicates that the cues provided in paragraph (a)(2)
of the proposals for identifying freezing rain/freezing drizzle
conditions are duplicated in material that appears in paragraph (a)(1)
of the proposals. The FAA infers from this remark that the commenter
requests that duplicative wording be removed from paragraph (a)(2) of
the proposed rules.
The FAA concurs. The FAA finds that the section entitled ``The
following shall be used to identify freezing rain/freezing drizzle
icing conditions'' is duplicated in material that appears in paragraph
(a)(1), and does not enhance the effectiveness of the AD's. Therefore,
that section has been removed from paragraph (a)(2) of the final rules
for all airplanes other than Aerospatiale Model ATR-42 and ATR-72
series airplanes.
Paragraph (a)(1) of the proposals for Aerospatiale airplanes
specified secondary indications for identifying possible freezing rain/
freezing drizzle conditions. The FAA recognizes that the flight crew
could have interpreted that paragraph to mean that if the secondary
indicators were observed, the airplane must be flown clear of the
severe icing conditions. However, the FAA's intent is that the flight
crew must immediately request priority handling to exit the icing
conditions only when the visual cue (ice on the side window) specified
in paragraph (a)(1) of the AD is observed.
Accordingly, the FAA has deleted the secondary indications of
possible severe icing conditions from paragraph (a)(1) of the final
rule for Aerospatiale airplanes. In addition, the FAA has removed the
visual cue (ice on the side window) from paragraph (a)(2) of the final
rule. The FAA has retitled the section containing the secondary
indications of possible severe icing as follows: ``The following may be
used as secondary indications of severe icing conditions.'' Further,
the last two secondary indicators contained in that section are
specified in the final rule in a section titled: ``The following
weather conditions may be conducive to severe in-flight icing.'' (This
change is explained further in Comment 51 below.)
Comment 51. Request To Remove Visual Cues: Identification of Possible
Freezing Rain/Freezing Drizzle
One commenter states that the word ``may'' in the following title,
which appears in paragraph (a)(2) of the proposals, is confusing: ``The
following may be used to identify possible freezing rain/freezing
drizzle conditions.'' The commenter indicates that AFM procedures
should provide a clear sequence of steps that must be followed and that
such procedures should be explicit; general advice, regardless of how
prudent, should be published elsewhere. The FAA infers from this remark
that the commenter asks that the cues that appear under this section be
deleted.
The FAA does not concur that this section should be removed. The
cues provided for identification of possible severe icing conditions
will alert the pilot to the possibility that unusual ice accretion may
develop. The FAA finds that the level of detail provided in the final
rules will increase the level of pilot awareness and, consequently,
will increase the level of safety over that which exists currently.
Therefore, the FAA has determined that it is appropriate to incorporate
this section in the AFM.
However, the FAA finds that clarification is necessary with regard
to the title of this section. The FAA finds that operators may
misinterpret that title, as proposed, to mean that this section
contains visual cues that should be used to identify possible severe
icing conditions prior to takeoff, dispatch, or release while the
airplane is on the ground. Additionally, the FAA finds that confusion
could result in differentiating between the weather conditions
specified in this section and the visual cues provided in paragraph
(a)(1) of the AD's. For clarification purposes, the FAA has revised the
title of this section to read as follows: ``The following weather
conditions may be conducive to severe in-flight icing.''
Comment 52. Request To Revise Air Temperature References
Transport Canada Aviation states that ambient temperature is
indicated as static air temperature (SAT), rather than outside air
temperature (OAT), for de Havilland Model DHC-8 series airplanes. The
FAA infers from this remark the commenter requests that the ambient
temperature that appears in the weather conditions specified in
paragraph (a)(2) of the proposals be expressed as SAT for those
airplanes.
The FAA does not concur. The FAA does not intend to specify which
specific indicator in the cockpit a pilot should use to determine the
ambient air temperature. The FAA intends that the pilot use whatever
means necessary to determine ambient air temperature.
However, since airplanes may have indicators other than OAT, the
FAA has replaced the words ``outside air temperature'' with ``ambient
air temperature'' in the weather conditions, and in the procedures for
exiting the severe icing environment, specified in paragraph (a)(2) of
these final rules to eliminate confusion concerning the need for a
specific type of indicator.
In addition, the FAA has re-examined the ambient temperature of +5
degrees Celsius that is specified in paragraph (a)(2) of the proposals.
The FAA has determined that this temperature is too high to be used as
a reliable indication of whether severe icing conditions may exist
during flight. The FAA finds that 0 degrees Celsius is a more
appropriate indication. The FAA has revised paragraph (a)(2) of the
final rules for all airplanes accordingly.
Comment 53. Request To Replace Reference to Droplets that Splash or
Splatter
JAL requests that the weather condition that pertains to ``droplets
that splash or splatter'' be removed from paragraph (a)(2) of the
proposals. JAL believes that this weather condition places too much
emphasis on subjective judgment. JAL states that normal rain conditions
will contain droplets that splash or splatter upon impact with the
windshield. JAL indicates that information included in its existing AFM
revisions, specified as follows, adequately addresses the issue:
``Prolonged operation in altitude bands where temperatures are near
freezing and heavy moisture is visible on the windscreen should be
avoided.''
The FAA does not concur that this weather condition should be
removed from the AD's. This weather condition must be used in
conjunction with the temperature specified as a means of identifying
severe in-flight icing conditions. The weather condition also will
alert the pilot to the possibility that unusual ice accretion may
develop. The FAA finds that the AFM information submitted by JAL does
not provide an equivalent alert to the pilot.
[[Page 20633]]
Comment 54. Request To Revise Procedures for Exiting Freezing Rain/
Freezing Drizzle
JAL requests that the procedures for exiting freezing rain/freezing
drizzle specified in paragraph (a)(2) of the proposals be restricted to
essential instructions that the flight crew must follow. JAL contends
that the procedures contained in the proposals are not written in the
appropriate format for AFM procedures, but are more representative of
advisory material. JAL also states that the current FAA- approved AFM
procedures for exiting freezing rain/freezing drizzle already provide
this essential information and conform to the existing style of the
AFM's. Transport Canada Aviation requests that the first instruction in
these procedures be revised to state only: ``Exit the freezing rain or
freezing drizzle conditions immediately.'' The commenter also requests
clarification of the terms ``extended exposure,'' as used in that
instruction.
The FAA concurs partially. The FAA has reviewed the procedures for
exiting the severe icing environment and finds that two of the
instructions contained in those procedures do not require the level of
detail provided in the proposed rules. The FAA finds that the
information concerning masking of control system forces is already
provided in the Limitations Section of the AFM. Therefore, the FAA has
revised the third instruction of those procedures to read as follows:
``Do not engage the autopilot.'' Additionally, the FAA has determined
that the flight crew need not be provided with instructions for
reducing the angle-of-attack because instructions such as this are
considered to be basic airmanship. Accordingly, the FAA has revised the
fifth instruction in the procedures for exiting the severe icing
environment to specify only information that is essential for the
flight crew. The revised instruction reads as follows: ``If an unusual
roll response . . . reduce the angle-of-attack.'' The FAA finds that,
for the remainder of the procedures for exiting, the additional level
of details provided in the final rules will increase the level of
understanding and, consequently, will increase the level of safety over
that which exists currently. The FAA finds that these procedures are
appropriate for insertion in the AFM's.
Regarding the terms ``extended exposure,'' the intent of that
instruction is to advise the flight crew that exiting the severe icing
conditions will minimize the exposure to flight conditions outside
those for which the airplane has been certificated. The FAA finds that
remaining in such conditions for a prolonged period may result in
accumulating an amount of ice sufficient to cause control problems. The
phrase ``to avoid extended exposure'' is only intended to explain to
the flight crew why severe icing conditions should be exited
immediately.
Raytheon questions the necessity to tell a commercial pilot not to
make any abrupt or excessive maneuvers if the aircraft is in the
position of having control difficulties. This instruction appears under
the heading ``Procedures for exiting the freezing rain/freezing drizzle
environment,'' which appears in paragraph (a)(2) of the proposals. The
commenter contends that this is a training issue and is not appropriate
for AFM procedures. The FAA infers from the commenter's remark that the
commenter requests that these instructions be eliminated from the
proposed rules.
The FAA does not concur. The FAA has determined that such
instructions provide beneficial guidance to the flight crew, which will
enhance the safety of the aircraft.
Saab requests that the FAA revise one of the instructions specified
in the procedures for exiting freezing rain/freezing drizzle specified
in the proposals. The instruction states that if an unusual roll
response or uncommanded control movement is observed, the angle-of-
attack should be reduced by increasing the airspeed or rolling the
wings level (if in a turn), and applying additional power, if needed.
Saab suggests that this instruction be revised to include the word
``aileron'' in the reference to uncommanded control movement. Saab
states further that in the case of wing ice beyond the protected
surfaces, the application of power may be appropriate to increase
airspeed/improve airflow. However, if ice has accrued on the wings
beyond the protected surfaces, there is a possibility that there also
is ice on the horizontal stabilizers. In this case, a sudden burst of
power may be detrimental. An uncommanded pitch control movement is
indicative of tail ice, which normally calls for a different action,
both concerning power as well as the handling of flaps, if extended.
Another commenter, Transport Canada Aviation, requests that the same
instruction be revised to include the word ``lateral'' in reference to
``uncommanded control movement,'' and to change the phrase ``or rolling
wings level'' to ``and rolling wings level.''
The FAA concurs partially. The FAA agrees that the correct
procedures for reducing the angle-of-attack is to increase the airspeed
and roll the wings level, if in a turn. However, as explained
previously, this portion of the procedure has been removed from the
final rules. The FAA does not agree that either ``lateral'' or
``aileron'' should be used to specify the type of uncommanded control
movement. The FAA finds that use of the term ``lateral'' may not be
understood by the flight crew. The FAA finds that including the word
``aileron'' may clarify which control surface is of concern; however,
the FAA has determined that use of a more general term, ``roll'' will
correctly specify the type of uncommanded control movement that is of
concern. The FAA has revised the fifth instruction in the procedures
for exiting the severe icing environment in paragraph (a)(2) of the
final rules accordingly. The revised instruction reads as follows: ``If
an unusual roll response or uncommanded roll control movement is
observed, reduce the angle-of-attack.''
In addition, the procedures for exiting the freezing rain/freezing
drizzle environment contained in the proposals did not specify to use
``a sudden burst of power'' when reducing the angle-of-attack. Rather,
the proposed procedure indicates to apply additional power, if needed,
to provide the desired flight path. However, as discussed previously,
the FAA has removed this reference from the final rules. In addition,
as explained previously, the FAA has revised the final rules to add the
word ``roll'' to describe the type of uncommanded control movement.
This revised wording addresses Saab's concern regarding increasing
power for a pitch anomaly.
Saab also notes that this instruction recommends a reduction in the
angle-of-attack and application of power, if needed. However, the next
instruction of the procedures indicates that reducing the angle-of-
attack may cause ice to build up beyond the protected areas of the
wing. Saab concludes that there is a conflict in that the proposed AD
would require that the angle-of- attack not be reduced or ice will
collect beyond the protected surfaces; however, the angle-of-attack
must be reduced if there is an unusual roll response or uncommanded
control movement.
The FAA does not concur with the commenter's contention that there
is a conflict in the AD's. Reducing the angle-of-attack by increasing
airspeed or rolling the wings level (if in a turn), and applying
additional power, if needed, is a procedure used to exit severe icing
conditions following an unusual roll response or uncommanded roll
control movement; whereas the instruction that involves not extending
the flaps during
[[Page 20634]]
extended operation in icing conditions is intended to prevent ice
build-up beyond the unprotected surfaces.
Raytheon asks for removal of the instruction to reduce the angle-
of-attack and apply additional power, if needed, in response to an
unusual roll response or uncommanded control movement. The commenter
states that these are normal instructions with respect to wing stall
and are inappropriate for inclusion in an AFM.
The FAA concurs partially. There may not be a stall warning
associated with uncommanded control movements in the case of encounters
with severe icing conditions. Since this is not a ``normal'' stall, the
flight crew may not recognize that normal stall recovery procedures
should be used. However, as stated previously, the instruction
referenced by the commenter has been deleted, in part, from the final
rules.
Raytheon also states that it is not appropriate to require contact
with Air Traffic Control as part of an AFM procedure since this is
already addressed in the Aeronautical Information Manual and in section
91.183 of the Federal Aviation Regulations (14 CFR 91.183). The FAA
infers from this statement that the commenter requests that the
instruction to contact Air Traffic Control should be removed from the
procedures for exiting severe icing conditions.
The FAA does not concur. The FAA is aware that this instruction is
contained in the references provided by the commenter. However, the FAA
finds that the importance of timely dissemination of this instruction
warrants its inclusion in the final rules. Inclusion of instructions of
this type is not without precedent; for example, similar information
also is specified in certain AFM's where the forward look windshear
system is addressed.
Comment 55. Request To Revise Procedures for Exiting the Severe Icing
Environment: Include Airplane- Specific Instructions
One commenter suggests that any action that might be necessary to
optimize aircraft performance and control in conditions of exceptional
icing, and exit from those conditions, should be determined separately
with each manufacturer; such procedures should be contained in the AFM
for each airplane model. The FAA infers from this remark that the
commenter requests that the FAA revise the procedures for exiting the
severe icing environment in each final rule to include airplane-
specific instructions.
The FAA agrees that procedures obtained from each individual
manufacturer should be considered and included in the final rules, if
appropriate. All manufacturers have been provided with an opportunity
to submit such procedures in response to the proposed rules. Some
manufacturers requested changes to the final rules. The FAA has revised
the final rules for those requests that were substantiated adequately.
Following issuance of the final rules, the FAA would consider a request
to include additional changes to the AFM revisions, in accordance with
the provisions of these AD's, provided that adequate justification is
presented to support such a request.
Comment 56. Revision of Procedures for Exiting the Severe Icing
Environment
The FAA has re-examined the section titled ``Procedures for exiting
the severe icing environment'' in paragraph (a)(2) of the proposals. As
proposed, that section states that if the visual cues used for
identifying ``possible'' freezing rain or freezing drizzle conditions
are observed, the flight crew should follow the procedures specified
for exiting those conditions. The FAA did not intend that the flight
crew use the procedures for exiting the severe icing environment when
the weather conditions specified in paragraph (a)(2) of these AD's are
observed. The FAA's intent is that the flight crew use those procedures
only when the visual cues identified in the Limitations Section of the
AFM are observed.
In order to eliminate any confusion, the FAA has revised the last
sentence of the first paragraph in the procedures for exiting the
severe icing environment. The FAA has removed the word ``possible''
from that sentence, and has added clarification that the visual cues
are specified in the Limitations Section of the AFM. The revised
sentence reads as follows: ``If the visual cues specified in the
Limitations Section of the AFM for identifying severe icing conditions
are observed, accomplish the following.'' (Operators should note that,
for Aerospatiale airplanes, the final rule specifies only one visual
cue, which involves ice on the side window.)
Comment 57. Request to Revise Cost Estimate
Transport Canada requests that the FAA provide an operational cost
estimate in the proposed AD's.
The FAA acknowledges the concern of the commenter. The FAA
recognizes that, in accomplishing the requirements of any AD, operators
may incur other 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 only includes such
direct costs. In the case of these AD's, 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.
Further, because AD's require specific actions to address specific
unsafe conditions, they appear to impose costs that would not otherwise
be borne by operators. However, because of the general obligation of
operators to maintain and operate aircraft in an airworthy condition,
this appearance is deceptive. Attributing those costs solely to the
issuance of this AD is unrealistic because, in the interest of
maintaining and operating safe aircraft, prudent operators would
accomplish the required actions even if they were not required to do so
by the AD. In any case, the FAA has determined that direct and
incidental costs are still outweighed by the safety benefits of the AD.
The FAA points out that it is not required to do a full cost-
benefit analysis for each AD. AD's were explicitly exempted from the
Office of Management and Budget (OMB) coordination process described in
Section 6 of that Executive Order. As a matter of law, in order to be
airworthy, an aircraft must conform to its type design and be in a
condition for safe operation. The type design is approved only after
the FAA makes a determination that it complies with all applicable
airworthiness requirements. In adopting and maintaining those
requirements, the FAA has already made the determination that they
establish a level of safety that is cost-beneficial. When the FAA later
makes a finding of an unsafe condition in an aircraft and issues an AD,
it means that the original cost beneficial level of safety is no longer
being achieved and that the required actions are necessary to restore
that level of safety. Because this level of safety has already been
determined to be cost beneficial, and because the AD does not add an
additional regulatory requirement that increases the level of safety
beyond what has been established by the type design, a full cost-
benefit analysis for each AD would be redundant and unnecessary.
Comment 58. Requests to Delay Issuance of the Final Rules
Three commenters request that the FAA extend the comment period for
the proposed rules by 90 days. Each of the commenters request the
extension in order to complete a comprehensive
[[Page 20635]]
analysis of this issue. The commenters state their involvement in
focusing on ``. . . ther recent rulemaking activity, including the
Commuter Rule, flight crewmember training requirements, and proposed
rules covering flight crew flight, duty and test requirements . . .''
as a reason that did not allow complete analysis of the proposed AD's.
One commenter requests that implementation of the AD's be deferred
until further discussion with industry has been undertaken.
The FAA has reviewed these requests and, in consideration of the
importance and need for dissemination of this important information to
the aviation community, does not concur that the comment period should
be extended or issuance of the final rules be deferred until a later
date. Issuing the final rules will ensure that the information is
available, understood, and implemented by the aviation community before
the next icing season. For these reasons, the FAA has determined that
it is imperative that the information and actions contained in these
final rules be incorporated into the operators' AFM's immediately.
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 previously
described. 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
The FAA estimates that 169 airplanes in the U.S. registry will be
affected by this AD, that it will take approximately 1 workhour per
airplane to accomplish the required action, and that the average labor
rate is approximately $60 an hour. Since an owner/operator who holds at
least a private pilot's certificate as authorized by sections 43.7 and
43.11 of the Federal Aviation Regulations (14 CFR 43.7 and 43.11) can
accomplish the required action, the only cost impact upon the public is
the time it would take the affected airplane owner/operators to
incorporate the AFM revisions.
In addition, the FAA recognizes that this AD may impose operational
costs. However, those costs are incalculable because the frequency of
occurrence of the specified conditions and the associated additional
flight time cannot be determined. Nevertheless, because of the severity
of the unsafe condition addressed, the FAA has determined that
continued operational safety necessitates the imposition of these
costs.
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 copy of the final evaluation 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, Aircraft, Aviation safety, Incorporation by
reference, 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 USC 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding a new airworthiness directive
(AD) to read as follows:
96-09-11 De Havilland: Amendment 39-9587; Docket No. 96-CE-01-AD.
Applicability: Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-
300 airplanes (all serial numbers), certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
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 (d) 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 minimize the potential hazards associated with operating the
airplane in severe icing conditions by providing more clearly
defined procedures and limitations associated with such conditions,
accomplish the following:
(a) Within 30 days after the effective date of this AD,
accomplish the requirements of paragraphs (a)(1) and (a)(2) of this
AD.
Note 2: Operators must initiate action to notify and ensure that
flight crewmembers are apprised of this change.
(1) Revise the FAA-approved Airplane Flight Manual (AFM) by
incorporating the following into the Limitations Section of the AFM.
This may be accomplished by inserting a copy of this AD in the AFM.
``WARNING
Severe icing may result from environmental conditions outside of
those for which the airplane is certificated. Flight in freezing
rain, freezing drizzle, or mixed icing conditions (supercooled
liquid water and ice crystals) may result in ice build-up on
protected surfaces exceeding the capability of the ice protection
system, or may result in ice forming aft of the protected surfaces.
This ice may not be shed using the ice protection systems, and may
seriously degrade the performance and controllability of the
airplane.
During flight, severe icing conditions that exceed
those for which the airplane is certificated shall be determined by
the following visual cues. If one or more of these visual cues
exists, immediately request priority handling from Air Traffic
Control to facilitate a route or an altitude change to exit the
icing conditions.
--Unusually extensive ice accreted on the airframe in areas not
normally observed to collect ice.
--Accumulation of ice on the upper surface of the wing aft of the
protected area.
--Accumulation of ice on the propeller spinner farther aft than
normally observed.
Since the autopilot may mask tactile cues that indicate
adverse changes in handling characteristics, use of the autopilot is
prohibited when any of the visual cues specified above exist, or
when unusual lateral trim requirements or autopilot trim warnings
are encountered while the airplane is in icing conditions.
All icing detection lights must be operative prior to
flight into icing conditions at night. [NOTE: This supersedes any
relief provided by the Master Minimum Equipment List (MMEL).]''
(2) Revise the FAA-approved AFM by incorporating the following
into the
[[Page 20636]]
Procedures Section of the AFM. This may be accomplished by inserting
a copy of this AD in the AFM.
``THE FOLLOWING WEATHER CONDITIONS MAY BE CONDUCIVE TO SEVERE IN-FLIGHT
ICING:
Visible rain at temperatures below 0 degrees Celsius
ambient air temperature.
Droplets that splash or splatter on impact at
temperatures below 0 degrees Celsius ambient air temperature.
PROCEDURES FOR EXITING THE SEVERE ICING ENVIRONMENT:
These procedures are applicable to all flight phases from
takeoff to landing. Monitor the ambient air temperature. While
severe icing may form at temperatures as cold as -18 degrees
Celsius, increased vigilance is warranted at temperatures around
freezing with visible moisture present. If the visual cues specified
in the Limitations Section of the AFM for identifying severe icing
conditions are observed, accomplish the following:
Immediately request priority handling from Air Traffic
Control to facilitate a route or an altitude change to exit the
severe icing conditions in order to avoid extended exposure to
flight conditions more severe than those for which the airplane has
been certificated.
Avoid abrupt and excessive maneuvering that may
exacerbate control difficulties.
Do not engage the autopilot.
If the autopilot is engaged, hold the control wheel
firmly and disengage the autopilot.
If an unusual roll response or uncommanded roll control
movement is observed, reduce the angle-of-attack.
Do not extend flaps during extended operation in icing
conditions. Operation with flaps extended can result in a reduced
wing angle-of-attack, with the possibility of ice forming on the
upper surface further aft on the wing than normal, possibly aft of
the protected area.
If the flaps are extended, do not retract them until
the airframe is clear of ice.
Report these weather conditions to Air Traffic
Control.''
(b) Incorporating the AFM revisions, as required by this AD, may
be performed by the owner/operator holding at least a private pilot
certificate as authorized by section 43.7 of the Federal Aviation
Regulations (14 CFR 43.7), and must be entered into the aircraft
records showing compliance with this AD in accordance with section
43.11 of the Federal Aviation Regulations (14 CFR 43.11).
(c) 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.
(d) 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, Small Airplane Directorate, FAA,
1201 Walnut, suite 900, Kansas City, Missouri 64106. The request
shall be forwarded through an appropriate FAA Maintenance Inspector,
who may add comments and then send it to the Manager, Small Airplane
Directorate.
Note 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Small Airplane Directorate.
(e) All persons affected by this directive may examine
information related to this AD at the FAA, Central Region, Office of
the Assistant Chief Counsel, Room 1558, 601 E. 12th Street, Kansas
City, Missouri 64106.
(f) This amendment (39-9587) becomes effective on June 11, 1996.
Issued in Kansas City, Missouri, on April 24, 1996.
Henry A. Armstrong,
Acting Manager, Small Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 96-10728 Filed 5-1-96; 3:23 pm]
BILLING CODE 4910-13-P