[Federal Register Volume 61, Number 17 (Thursday, January 25, 1996)]
[Proposed Rules]
[Pages 2151-2154]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-1171]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-22-AD]


Airworthiness Directives; Short Brothers Model SD3-30, SD3-60, 
and SD3-SHERPA Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to all Short Brothers Model SD3-30, 
SD3-60, and SD3-SHERPA series airplanes. This proposal would 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. This proposal 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 the proposed 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.

DATES: Comments must be received by March 7, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-22-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    This information may be examined at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT: Phil Forde, Aerospace Engineer, 
Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 
227-2146; fax (206) 227-1149.

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice 

[[Page 2152]]
must submit a self-addressed, stamped postcard on which the following 
statement is made: ``Comments to Docket Number 96-NM-22-AD.'' The 
postcard will be date stamped and returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 96-NM-22-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    In October 1994, a transport category airplane was involved in an 
accident in which severe icing conditions (believed to be composed of 
freezing drizzle size droplets) were reported in the area. Although the 
National Transportation Safety Board (NTSB) has not yet made a finding 
of probable cause of the accident, loss of control of the airplane may 
have occurred because ice accretion on the upper surface of the wing 
aft of the area protected by the ice protection system caused airflow 
separation, which resulted in the ailerons being forced to a right-
wing-down control position. There also is concern that the autopilot, 
which was engaged, may have masked the unusual control forces generated 
by the ice accumulation. These conditions, if not corrected, could 
result in a roll upset from which the flight crew may be unable to 
recover.
    The atmospheric conditions (freezing drizzle) that may have 
contributed to the accident are outside the icing envelope specified in 
Appendix C of part 25 of the Federal Aviation Regulations (14 CFR part 
25) for certification of the airplane. Freezing rain is an atmospheric 
condition that also is outside the icing envelope. Such icing 
conditions are not defined in Appendix C, and the FAA has not required 
that airplanes be shown to be capable of operating safely in those 
icing conditions.
    The FAA finds that flight crews are not currently provided with 
adequate information necessary to determine when the airplane is 
operating in icing conditions for which the airplane is not 
certificated or what action to take when such conditions are 
encountered. Therefore, the FAA has determined that flight crews must 
be provided with such information and must be made aware of certain 
visual cues that may indicate the airplane is operating in atmospheric 
conditions that are outside the icing envelope.
    Since such information is not available to flight crews, and no 
airplane is certificated for operation in freezing drizzle conditions, 
the FAA finds that the potentially unsafe condition (described 
previously as control difficulties following operation of the airplane 
in icing conditions outside of the icing envelope) is not limited to 
airplanes having the same type design as that of the accident airplane.
    The FAA recognizes that the flight crew of any airplane that is 
certificated for flight in icing conditions may not have adequate 
information concerning flight in icing conditions outside the icing 
envelope. However, the FAA finds that the specified unsafe condition 
must be addressed as a higher priority on airplanes that are 
turbopropeller-powered and have unpowered control systems. Many of 
these airplanes carry passengers in regularly scheduled revenue service 
in the United States. 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. Additionally, 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.
    Subsequent to the accident, the FAA, in conjunction with certain 
foreign airworthiness authorities and airplane manufacturers, conducted 
reviews of certain transport and small category airplanes to determine 
if any airplanes might experience control difficulty should a ridge of 
ice form aft of the deicing boots and forward of the ailerons. The 
review focused on turbopropeller-powered airplanes having unpowered 
roll control systems, since those airplanes are similar in design to 
the accident airplane and because they are frequently exposed to icing 
conditions.
    During the reviews of these airplanes, an artificial ice shape was 
used in the demonstration of roll control characteristics. This ice 
shape was chosen as representative of a shape that might form if an 
airplane were operated in freezing drizzle. Results of these reviews 
revealed that certain airplanes demonstrated acceptable roll control 
forces. However, the dynamics of ice accretion in freezing drizzle are 
not well understood, and the FAA recognizes that such airplanes could 
develop ice shapes other than those tested during the review. Upon 
further review, the FAA may consider additional rulemaking.
    Following examination of all relevant information, the FAA has 
determined that certain limitations and procedures should be included 
in the FAA-approved Airplane Flight Manual (AFM) for the affected 
airplanes, as follows:
    <bullet> Shorts Model SD3-30, SD3-60, and SD3-SHERPA series 
airplanes must be prohibited from flight in freezing rain or freezing 
drizzle conditions (as determined by certain visual cues); and
    <bullet> Flight crews must be provided with information that would 
minimize the potential hazards associated with operating the airplane 
in freezing rain or freezing drizzle conditions.

The FAA has determined that such limitations and procedures currently 
are not defined adequately in the AFM for these airplanes.
    These airplane models are manufactured in the United Kingdom and 
are type certificated for operation in the United States under the 
provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 
21.29) and the applicable bilateral airworthiness agreement.

Explanation of the Provisions of the Proposed AD

    Since an unsafe condition has been identified that is likely to 
exist or develop on other airplanes of the same type design, the 
proposed AD would require revising the Limitations Section of the AFM 
to specify procedures that would:
    <bullet> Prohibit flight in freezing rain or freezing drizzle 
conditions (as determined by certain visual cues);
    <bullet> Prohibit use of the autopilot when ice is formed aft of 
the protected surfaces of the wing, or when an unusual lateral trim 
condition exists; and
    <bullet> Require that all icing detection lights be operative prior 
to flight into icing conditions at night.
    The prohibition on flight in freezing rain or freezing drizzle is 
not intended to prohibit purely inadvertent encounters with the 
specified atmospheric conditions. However, pilots should make all 
reasonable efforts to avoid such encounters and must immediately exit 
the conditions if they are encountered.
    This proposed AD also would require revising the Normal Procedures 
Section of the AFM to specify procedures that would:
    <bullet> Limit the use of the flaps and prohibit the use of the 
autopilot when ice is observed forming aft of the protected surfaces of 
the wing, or if 

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unusual lateral trim requirements or autopilot trim warnings are 
encountered; and
    <bullet> Provide the flight crew with recognition cues for, and 
procedures for exiting from, severe icing conditions.

Cost Impact

    The FAA estimates that 138 airplanes of U.S. registry would be 
affected by this proposed AD, that it would take approximately 1 work 
hour per airplane to accomplish the proposed actions, and that the 
average labor rate is $60 per work hour. Based on these figures, the 
cost impact of the proposed AD on U.S. operators is estimated to be 
$8,280, or $60 per airplane.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the proposed requirements of 
this AD action, and that no operator would accomplish those actions in 
the future if this AD were not adopted.
    In addition, the FAA recognizes that this proposed 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 are indeterminable. 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 proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory 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, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
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 the following new 
airworthiness directive:

Short Brothers, PLC: Docket 96-NM-22-AD.
    Applicability: All Model SD3-30, SD3-60, and SD3-SHERPA series 
airplanes, 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 use the authority 
provided in paragraph (b) of this AD to request approval from the 
FAA. This approval may address either no action, if the current 
configuration eliminates the unsafe condition; or different actions 
necessary to address the unsafe condition described in this AD. Such 
a request should include an assessment of the effect of the changed 
configuration on the unsafe condition addressed by this AD. In no 
case does the presence of any modification, alteration, or repair 
remove any airplane from the applicability of this AD.

    Compliance: Required as indicated, unless accomplished 
previously.
    To minimize the potential hazards associated with operating the 
airplane in freezing rain or freezing drizzle 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.
    ``<bullet> Flight in meteorological conditions described as 
freezing rain or freezing drizzle, as determined by the following 
visual cues, is prohibited:
--Unusually extensive ice accreted on the airframe in areas not 
normally observed to collect ice.
--Accumulation of ice on the upper surface (for low-wing airplanes) 
or lower surface (for high-wing airplanes) of the wing aft of the 
protected area.
--Accumulation of ice on the propeller spinner farther back than 
normally observed.
    If the airplane encounters conditions that are determined to 
contain freezing rain or freezing drizzle, the pilot must 
immediately exit the freezing rain or freezing drizzle conditions by 
changing altitude or course.

    Note: The prohibition on flight in freezing rain or freezing 
drizzle is not intended to prohibit purely inadvertent encounters 
with the specified meteorological conditions. However, pilots should 
make all reasonable efforts to avoid such encounters and must 
immediately exit the conditions if they are encountered.

    <bullet> 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.

    Note: The autopilot may mask tactile cues that indicate adverse 
changes in handling characteristics. Therefore, the pilot should 
consider not using the autopilot when any ice is visible on the 
airplane.

    <bullet> 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 Normal Procedures Section of the AFM. This may be 
accomplished by inserting a copy of this AD in the AFM.

``WARNING

    ``If ice is observed forming aft of the protected surfaces of 
the wing, or if unusual lateral trim requirements or autopilot trim 
warnings are encountered:
    <bullet> If the flaps are extended, do not retract them until 
the airframe is clear of ice.
    <bullet> The flight crew should reduce the angle-of-attack by 
increasing speed as much as the airplane configuration and weather 
allow, without exceeding design maneuvering speed.
    <bullet> If the autopilot is engaged, hold the control wheel 
firmly and disengage the autopilot. Do not re-engage the autopilot 
until the airframe is clear of ice.
    <bullet> Exit the icing area immediately by changing altitude or 
course.
    <bullet> Report these weather conditions to Air Traffic Control.

CAUTION

    Severe icing comprises 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 extreme 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 

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ice protection systems, and may seriously degrade the performance and 
controllability of the airplane.

THE FOLLOWING SHALL BE USED TO IDENTIFY FREEZING RAIN/FREEZING DRIZZLE 
ICING CONDITIONS:

    <bullet> Unusually extensive ice accreted on the airframe in 
areas not normally observed to collect ice.
    <bullet> Accumulation of ice on the upper surface (for low-wing 
airplanes) or lower surface (for high-wing airplanes) of the wing 
aft of the protected area.
    <bullet> Accumulation of ice on the propeller spinner farther 
back than normally observed.

THE FOLLOWING MAY BE USED TO IDENTIFY POSSIBLE FREEZING RAIN/FREEZING 
DRIZZLE CONDITIONS:

    <bullet> Visible rain at temperatures below +5 degrees Celsius 
[outside air temperature (OAT)].
    <bullet> Droplets that splash or splatter on impact at 
temperatures below +5 degrees Celsius OAT.

PROCEDURES FOR EXITING THE FREEZING RAIN/FREEZING DRIZZLE ENVIRONMENT:

    These procedures are applicable to all flight phases from 
takeoff to landing. Monitor the outside 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 AFM for identifying possible freezing rain or freezing 
drizzle conditions are observed, accomplish the following:
    <bullet> Exit the freezing rain or freezing drizzle severe icing 
conditions immediately to avoid extended exposure to flight 
conditions outside of those for which the airplane has been 
certificated for operation. Asking for priority to leave the area is 
fully justified under these conditions.
    <bullet> Avoid abrupt and excessive maneuvering that may 
exacerbate control difficulties.
    <bullet> Do not engage the autopilot. The autopilot may mask 
unusual control system forces.
    <bullet> If the autopilot is engaged, hold the control wheel 
firmly and disengage the autopilot.
    <bullet> If an unusual roll response or uncommanded control 
movement is observed, reduce the angle-of-attack by increasing 
airspeed or rolling wings level (if in a turn), and apply additional 
power, if needed.
    <bullet> Avoid extending flaps during extended operation in 
icing conditions. Operation with flaps extended can result in a 
reduced wing angle-of-attack, with ice forming on the upper surface 
further aft on the wing than normal, possibly aft of the protected 
area.
    <bullet> Report these weather conditions to Air Traffic 
Control.''
    (b) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Standardization Branch, ANM-113, 
FAA, Transport Airplane Directorate. Operators shall submit their 
requests through an appropriate FAA Principal Operations Inspector, 
who may add comments and then send it to the Manager, 
Standardization Branch, ANM-113.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Standardization Branch, ANM-113.

    (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.

    Issued in Renton, Washington, on January 19, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-1171 Filed 1-24-96; 8:45 am]
BILLING CODE 4910-13-U