[Federal Register Volume 65, Number 54 (Monday, March 20, 2000)]
[Rules and Regulations]
[Pages 14822-14825]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-6616]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-CE-44-AD; Amendment 39-11643; AD 2000-06-03]
RIN 2120-AA64


Airworthiness Directives; Bombardier Inc. Models DHC-6-1, DHC-6-
100, DHC-6-200, and DHC-6-300 Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

-----------------------------------------------------------------------

SUMMARY: This document adopts a new airworthiness directive (AD) that 
applies to all Bombardier Inc. (Bombardier) Models DHC-6-1, DHC-6-100, 
DHC-6-200, and DHC-6-300 airplanes that are equipped with pneumatic 
deicing boots. This AD requires revising the Airplane Flight Manual 
(AFM) to include requirements for activation of the airframe pneumatic 
deicing boots. This AD is the result of reports of in-flight incidents 
and an accident that occurred in icing conditions where the airframe 
pneumatic deicing boots were not activated. The actions specified by 
this AD are intended to assure that flightcrews activate the pneumatic 
wing and tail deicing boots at the first signs of ice accumulation. 
This action will prevent reduced controllability of the aircraft due to 
adverse aerodynamic effects of ice adhering to the airplane prior to 
the first deicing cycle.

EFFECTIVE DATE: May 5, 2000.

ADDRESSES: You may examine information related to this AD at the 
Federal Aviation Administration (FAA), Central Region, Office of the 
Regional Counsel, Attention: Rules Docket No. 99-CE-44-AD, 901 Locust, 
Room 506, Kansas City, Missouri 64106.

FOR FURTHER INFORMATION CONTACT: Mr. John P. Dow, Sr., Aerospace 
Engineer, FAA, Small Airplane Directorate, 901 Locust, Room 506, Kansas 
City, Missouri 64106; telephone: (816) 329-4121; facsimile: (816) 329-
4090.

SUPPLEMENTARY INFORMATION:

Events Leading to the Issuance of This AD

    What caused this AD?: This AD is the result of reports of in-flight 
incidents and an accident that occurred in icing conditions where the 
airframe pneumatic deicing boots were not activated.
    What is the potential impact if the FAA took no action?: The 
information necessary to activate the pneumatic wing and tail deicing 
boots at the first signs of ice accumulation is critical for flight in 
icing conditions. If we did not take action to include this 
information, flight crews could experience reduced controllability of 
the aircraft due to adverse aerodynamic effects of ice adhering to the 
airplane prior to the first deicing cycle.
    Has the FAA taken any action to this point?: Yes. We issued a 
proposal to amend part 39 of the Federal Aviation Regulations (14 CFR 
part 39) to include an AD that would apply to all Bombardier Models 
DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes that are 
equipped with pneumatic deicing boots. This proposal was published in 
the Federal Register as a notice of proposed rulemaking (NPRM) on 
October 12, 1999 (64 FR 55201). The NPRM proposed to require revising 
the Limitations Section of the AFM to include requirements for 
activating the pneumatic deicing boots at the first indication of ice 
accumulation on the airplane.
    Was the public invited to comment?: Yes. Interested persons were 
afforded an opportunity to participate in the making of this amendment. 
The following paragraphs present the comments received on the NPRM. 
Also included is the FAA's response to each comment, including any 
changes incorporated into the final rule based on the comments.

Comment Issue No. 1: Coordinate With Original Equipment 
Manufacturer

    What is the Commenter's Concern?: One commenter states that the FAA 
should coordinate with the original equipment manufacturer before 
issuing the AD.
    What is the FAA's Response to the Concern?: We concur.
    The FAA coordinates and will continue to coordinate with the 
manufacturer of any affected airplanes before issuing an AD.
    Is it Necessary to Change the AD?: No.

Comment Issue No. 2: Provide the Criteria for Determining 
Acceptable Stall Warning Margins

    What is the Commenter's Concern?: One commenter requests that the 
FAA provide the criteria for determining whether an airplane has an 
acceptable stall warning margin. The commenter references recent NPRM 
AD withdrawals in the FAA's Transport Airplane Directorate.
    What is the FAA's Response to the Concern?: We cannot provide such 
information because no regulatory basis exists for determining or 
applying a mandatory stall margin with contamination. We can review 
manufacturer-provided data to determine what testing was conducted, and 
then determine the effects of ice accretion on the stall angle and the 
handling characteristics in the roll axis. This would include reviewing 
the service history of each airplane. With all of this information, we 
could determine whether the stall warning margin was acceptable and if 
the AD action could be withdrawn.
    Such was the case with the NPRM withdrawals in the FAA's Transport 
Airplane Directorate. The airplanes affected were Cessna Models 500, 
501, 550, 551, and 560 series airplanes, and British Aerospace 
Jetstream Model 4101 airplanes. You may find the specific justification 
for each of these withdrawals in the Federal Register through the 
following citations:

--For the Cessna airplanes: 64 FR 62995, November 18, 1999; and -For 
the Jetstream airplanes: 64 FR 62990, November 18, 1999.

    No specific information was submitted for the Bombardier DHC-6 
series airplanes.
    Is it Necessary to Change the AD?: No.

Comment Issue No. 3: Review the Effects of Ice Bridging

    What is the Commenter's Concerns?: A commenter states that the FAA 
did not reference in the NPRM any testing to assure that ice bridging 
does not exist on any of the affected airplanes. This commenter 
requests that the FAA carefully review the effects of ice bridging. Ice 
bridging, as referred to in the aviation community, occurs when the 
mechanical deicing boots do not clear airframe icing from the wing 
surface. This occurs because the ``ice bridge'' that forms over the 
inflated boots increases in ice thickness while the deicing boots 
ineffectively inflate and deflate under the ice bridge.
    The commenter also requests explanation on the use of the term 
``modern'' in a similar AD action that

[[Page 14823]]

the FAA's Transport Airplane Directorate initiated.
    What is the FAA's Response to the Concerns?: The FAA considered the 
effects of ice bridging while developing the AD. We consulted the 
aviation community, including airframe manufacturers, air carriers, 
airline pilot associations, airplane owner associations, deicing boot 
manufacturers, and the National Aeronautics and Space Administration 
(NASA). Based on information from the aviation community, we believe 
that little evidence of ice bridging exists as it relates to current 
deicing boot designs. Also, ice that is not shed after the initial boot 
cycle continues to increase in thickness and sheds during subsequent 
cycles.
    The FAA's Transport Airplane Directorate addressed the issue of 
``modern'' versus ``older'' pneumatic boot systems in a recent AD 
action. That information, in its entirety, follows:

    ``Several commenters request that the difference between the 
``older'' and ``modern'' boot systems be explained. These commenters 
express concern that although both systems are addressed in the 
proposal, there may not be a sound technical reason to apply the 
requirements of the proposal to both types of boot systems.
    The FAA acknowledges that definitions of ``older'' and 
``modern'' pneumatic boot systems should be provided. Therefore, for 
the purposes of this AD, ``modern'' pneumatic boot systems may be 
characterized by short segmented, small diameter tubes, which are 
operated at relatively high pressures [18-23 pounds per square inch 
(psi)] by excess bleed air that is provided by turbine engines. 
``Older'' pneumatic boot systems may be characterized by long, 
uninterrupted, large diameter tubes, which were operated at low 
pressures by engine driven pneumatic pumps whose pressure varied 
with engine revolutions per minute (rpm). This low pressure coupled 
with long and large diameter tubes caused early deice systems to 
have very lengthy inflation and deflation cycles and dwell times. 
(Dwell time is the period of time that the boot remains fully 
expanded following the completion of the inflation cycle until the 
beginning of the deflation cycle.)''

    Is it Necessary to Change the AD?: No.

Comment Issue No. 4: Limit the AFM Change to Approach and Hold 
Phases of Flight

    What is the Commenter's Concern? One commenter requests that the 
FAA limit the AFM change of operating the boots at the first sign of 
ice accretion to the approach and hold phases of flight. This commenter 
references the work that the Ice Protection Harmonization Working Group 
(IPHWP) is currently doing. The commenter states that the IPHWP 
believes that the only phases of flight that demonstrate a safety 
concern are holding patterns and various approach segments. Since these 
operations occur at lower speeds, ice accumulating on the wing and tail 
surfaces could cause instability.
    What is the FAA's Response to the Concern? We do not concur to 
limiting the AFM change to the holding and approach phases of flight. 
We acknowledge that the IPHWG is working on a proposed operations rule. 
The IPHWG continues to work on this proposed rule and has not reached 
technical agreement. We have records of in-flight roll upsets in icing 
during the climb and cruise phases of flight on small airplanes that 
are of a similar type design to the Bombardier DHC-6 series airplanes.
    We concur that the ice protection system should not be operated at 
times when no ice is accreting. We have changed the description of the 
atmospheric conditions that the deicing boots must be operated from 
``icing conditions'' to ``known or observed/detected icing that the 
flight crew visually observed on the aircraft or was identified by the 
on-board sensors.''
    Is it Necessary to Change the AD?: Yes. We have made the change 
described above in the final rule.

Comment Issue No. 5: Conduct Further Testing Before Issuing the AD

    What is the Commenter's Concern? One commenter requests that the 
FAA conduct more tests before proceeding with this AD action. The 
commenter agrees that operating the pneumatic boots continuously is the 
best way to identify ice accretion. However, the commenter states 
concern over the residual ice that could accumulate in this mode. The 
commenter recommends the following:
    --The FAA research the possibility of mandating the installation of 
a reliable ice detection system to alleviate the difficulties 
associated with flightcrew recognition of airfoil ice accretions;
    --The FAA work together with the manufacturers to determine how 
efficient the pneumatic boots are in shedding significant thinner ice 
accretions than encountered previously; and
    --The FAA quantify the performance effects of prolonged operation 
with residual ice on the airfoil prior to implementing any new boot 
operation procedures.
    What is the FAA's Response to the Concern? We do not concur with 
the concerns over residual ice. Operation of the pneumatic deicing 
boots typically results in persistent ice accretions on the boots 
surfaces, even with 1/4-inch to 1/2-inch of ice accretion prior to 
activation of the boots. The persistent residual and inter-cycle ice 
accretions typically result in adverse aerodynamic effects and degraded 
airplane flying qualities. Activating the wing and tail pneumatic 
deicing boots at the first sign of ice accretion (or at the 
annunciation of an ice detector system) and periodically operating the 
deicing boots will result in persistent ice accretions.
    However, the proposed actions will minimize the residual and 
intercycle ice accretions because the ice will shed when the minimum 
thickness or mass required for shedding is reached. The residual and 
intercycle ice accretion thickness that results from this procedure is 
less than the ice accretion thickness typically recommended prior to 
operation of the pneumatic deicing boot. The thickness, shape, texture, 
and location of the ice accretion affect the adverse airplane flying 
qualities that result from ice accretions.
    Certain airplane manufacturers have previously issued AFM 
information that contains procedures to activate the deicing boots at 
the first sign of ice accumulation. We have received no reports 
indicating any adverse effects of residual ice because of early 
activation of the deicing boots for these airplane designs.
    Those airplane models that are equipped with deicing boot systems 
with automatic operating modes result in operation of the boots with 
less than the recommended thickness of accreted ice. We have received 
no reports indicating any adverse effects resulting from the use of the 
automatic mode.
    We concur that the installation of a reliable ice detection system 
would alleviate the difficulties associated with flightcrew recognition 
of airfoil ice accretion. We are working with industry on the 
possibility of developing such a system. If developed, tested, and 
approved, the FAA may consider additional rulemaking. For the time 
being, we are issuing this AD to impose a deicing boot operation change 
to address the reduced handling qualities or controllability problems 
associated with ice accretion on the protected surfaces.
    Is it Necessary to Change the AD? No.

Comment Issue No. 6: Require Action to Reduce Adhesion 
Characteristics

    What is the Commenter's Concern? One commenter requests that the 
FAA mandate actions to minimize or reduce the ice adhesion 
characteristics of boot material. The commenter states that one reason 
flightcrews see large amounts of residual ice is because residual ice

[[Page 14824]]

sticks to the boot surface as the boot ages. This may increase if the 
adhesion qualities of the boot material are not maintained. The 
commenter suggests the use of certain compounds, such as ICEX \TM\ (an 
ice-phobic chemical spray), to reduce ice adhesion.
    What is the FAA's Response to the Concern?: We concur that 
materials such as ICEX \TM\ could reduce ice adhesion. However, factors 
such as normal wear and tear, patching, and oxidation of boot material, 
prevent us from establishing an effective level of application or 
adequate intervals of application. We will include a NOTE in the AD to 
recommend regular treatment of deicing boots with use of approved ice 
release agents. This is in addition to the required actions.
    Is it Necessary to Change the AD?: No. However, as discussed above, 
the FAA is including a NOTE in the AD to recommend regular treatment of 
deicing boots with use of approved ice release agents.

The FAA's Determination

    What is the FAA's final determination on this issue? After careful 
review of all available information related to the subject presented 
above, we have determined that air safety and the public interest 
require the adoption of the rule as proposed except for the following:
--The change in the description of the atmospheric conditions that the 
deicing boots must be operated;
--The addition of the NOTE to recommend regular treatment of deicing 
boots with use of approved ice release agents; and
--Minor editorial corrections.

    How does the change, addition, and corrections affect the AD?: We 
have determined that the change, addition, and minor corrections will 
not change the meaning of the AD and will not add any additional burden 
upon the public than was already proposed.

Cost Impact

    How many airplanes does this AD impact?: We estimate that 162 
airplanes in the U.S. registry will be affected.
    What is the cost impact of the affected airplanes on the U.S. 
Register?: There is no dollar cost impact. We estimate that to 
accomplish the AFM revision it will take you less than 1 workhour. You 
can accomplish this action if you hold at least a private pilot 
certificate as authorized by section 43.7 of the Federal Aviation 
Regulations (14 CFR 43.7). You must make an entry into the aircraft 
records that shows compliance with this AD, in accordance with section 
43.9 of the Federal Aviation Regulations (14 CFR 43.9). The only cost 
impact of this AD is the time it will take you to insert the 
information into the AFM.

Regulatory Impact

    The regulations adopted herein will not have a substantial direct 
effect 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, it 
is determined that this final rule does not have federalism 
implications under Executive Order 13132.
    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, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends part 39 of 
the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding a new airworthiness directive 
(AD) to read as follows:

2000-06-03 Bombardier Inc.: Amendment 39-11643; Docket No. 99-CE-44-
AD.

    (a) What airplanes are affected by this AD?
    Models DHC-6-1, DHC-6-100, DHC-6-200, DHC-6-300 airplanes, all 
serial numbers, that are:
    (1) Equipped with pneumatic deicing boots; and
    (2) Certificated in any category.
    (b) Who must comply with this AD? Anyone who wishes to operate 
any of the above airplanes on the U.S. Register. The AD does not 
apply to your airplane if it is not equipped with pneumatic de-icing 
boots.
    (c) What problem does this AD address? The information necessary 
to activate the pneumatic wing and tail deicing boots at the first 
signs of ice accumulation is critical for flight in icing 
conditions. If we did not take action to include this information, 
flight crews could experience reduced controllability of the 
aircraft due to adverse aerodynamic effects of ice adhering to the 
airplane prior to the first deicing cycle.
    (d) What must I do to address this problem?: To address this 
problem, you must revise the Limitations Section of the FAA-approved 
Airplane Flight Manual (AFM) to include the following requirements 
for activation of the ice protection systems. You must accomplish 
this action within the next 10 calendar days after the effective 
date of this AD, unless already accomplished. You may insert a copy 
of this AD in the AFM to accomplish this action:
     ``Except for certain phases of flight where the AFM 
specifies that deicing boots should not be used (e.g., take-off, 
final approach, and landing), compliance with the following is 
required.
     Wing and Tail Leading Edge Pneumatic Deicing Boot 
System, if installed, must be activated:
    --At the first sign of ice formation anywhere on the aircraft, 
or upon annunciation from an ice detector system, whichever occurs 
first; and
    --The system must either be continued to be operated in the 
automatic cycling mode, if available; or the system must be manually 
cycled as needed to minimize the ice accretions on the airframe.
     The wing and tail leading edge pneumatic deicing boot 
system may be deactivated only after:
    --Leaving known or observed/detected icing that the flight crew 
has visually observed on the aircraft or was identified by the on-
board sensors; and
    --After the airplane is determined to be clear of ice.''

    Note: The FAA recommends periodic treatment of deicing boots 
with approved ice release agents, such as ICEX \TM\, in accorance 
with the manufacturer's application instructions.

    (e) Can the pilot accomplish the action? Yes. Anyone who holds 
at least a private pilot certificate, as authorized by section 43.7 
of the Federal Aviation Regulations (14 CFR 43.7), may incorporate 
the AFM revisions required by this AD. You must make an entry into 
the aircraft records that shows compliance with this AD, in 
accordance with section 43.9 of the Federal Aviation Regulations (14 
CFR 43.9).
    (f) Can I comply with this AD in any other way? Yes.
    (1) You may use an alternative method of compliance or adjust 
the compliance time if:
    (i) Your alternative method of compliance provides an equivalent 
level of safety; and
    (ii) The Manager, Small Airplane Directorate, approves your 
alternative. Submit your request through an FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager.

[[Page 14825]]

    (2) 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 (f)(1) 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 you have not eliminated the unsafe 
condition, specific actions you propose to address it.
    (g) Where can I get information about any already-approved 
alternative methods of compliance? Contact the Small Airplane 
Directorate, 901 Locust, Room 301, Kansas City, Missouri 64106; 
telephone: (816) 329-4121; facsimile: (816) 329-4091.
    (h) What if I need to fly the airplane to another location to 
comply with this AD? The FAA can issue a special flight permit under 
Secs. 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 
21.197 and 21.199) to operate your airplane to a location where you 
can accomplish the requirements of this AD.
    (i) When does this amendment become effective? This amendment 
becomes effective on May 5, 2000.

    Issued in Kansas City, Missouri, on March 10, 2000.
Michael Gallagher,
Manager, Small Airplane Directorate, Aircraft Certification Service.
[FR Doc. 00-6616 Filed 3-17-00; 8:45 am]
BILLING CODE 4910-13-U