[Federal Register Volume 61, Number 93 (Monday, May 13, 1996)]
[Proposed Rules]
[Pages 21982-21984]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-11881]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-63-AD]
RIN 2120-AA64


Airworthiness Directives; Gates Learjet Model 35 and 36 Series 
Airplanes Modified by Raisbeck STC SA766NW

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 certain Gates Learjet Model 35 and 
36 series airplanes that have been modified in accordance with Raisbeck 
Supplemental Type Certificate (STC) SA766NW. This proposal would 
require a reduction of the maximum operating limit speed on the 
affected airplanes to prevent encountering certain potentially 
hazardous conditions. This proposal is prompted by reports of incidents 
of aileron buffet or buzz experienced during high speed cruise. The 
actions specified by the proposed AD are intended to prevent aileron 
buffet or buzz conditions, which can result in the deterioration of the 
aircraft lateral control system characteristics to an unacceptable 
level.

DATES: Comments must be received by June 24, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-63-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.
    Information concerning the subject of this rulemaking action may be 
obtained from Jet Air Corporation, P.O. Box 245, Bellevue, Washington 
98009. Information concerning this rulemaking action may be examined at 
the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Stan Wood, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2772; 
fax (206) 227-1181.

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 must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-63-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-63-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On July 23, 1985, the FAA issued AD 85-16-04, amendment 39-5110 (50 
FR 30803, July 30, 1985), which is applicable to certain Gates Learjet 
Model 35 and 36 series airplanes that have been modified in accordance 
with Raisbeck Supplemental Type Certificate (STC) SA766NW. That AD 
requires the accomplishment of one of two optional actions, both of 
which are intended to prevent the airplane from encountering the 
potentially hazardous condition of aileron buffet or buzz:
    1. One optional action requires operators to reduce permanently the 
maximum operating Mach limit (M<INF>MO) of these airplanes from .83 to 
.80. This action includes resetting the Mach

[[Page 21983]]

overspeed warning switch; recalibrating the airspeed indicator; and 
changing the FAA-approved Airplane Flight Manual (AFM) Supplement to 
reflect the new Mach limit.
    2. The other optional action requires operators to remove the 
Raisbeck STC modifications and to return the airplane either to its 
original configuration or to the Gates Learjet ``Softflight'' 
configuration.
    AD 85-16-04 was prompted by several reports of incidents in which 
Learjet Model 35 and 36 series airplanes modified with the Raisbeck STC 
experienced aileron buffet or buzz during cruise. These incidents of 
aileron instability occurred on airplanes operating at high gross 
weights when they were flying above 42,000 feet at Mach .80 to .83. 
Aileron buffet or buzz, if it is of a certain severity, can result in 
an unacceptable deterioration in the lateral control characteristics of 
the airplane.

Actions Subsequent to the Issuance of AD 85-16-04

    When AD 85-16-04 was issued, its applicability included only 
certain modified airplanes, which were identified by specific serial 
numbers. However, since the issuance of that AD, the FAA has received a 
report that at least one additional airplane, that was not included in 
the applicability of the AD, has been modified in accordance with the 
subject Raisbeck STC. (The STC installed on this particular airplane 
was performed at a non-U.S. repair station.) In light of this, that 
airplane may be subject to the same unsafe condition addressed by AD 
85-16-04.
    Further, since the Raisbeck STC could be installed on Model 35 or 
36 series airplanes anywhere in the world, the FAA may not be 
immediately aware of it. Therefore, the FAA has determined that any of 
these airplanes on which the Raisbeck STC is installed could be subject 
to that same unsafe condition.

Description of the Proposed AD

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require the accomplishment of one of two optional 
actions, both of which are intended to prevent the airplane from 
encountering the potentially hazardous condition of aileron buffet or 
buzz:
    1. Permanently reducing the maximum operating M<INF>MO from .83 to 
.80; resetting the Mach overspeed warning switch; recalibrating the 
airspeed indicator; and changing the FAA-approved Airplane Flight 
Manual (AFM) Supplement to reflect the new Mach limit; or
    2. Removing the Raisbeck STC modifications and returning the 
airplane either to its original configuration or to the Gates Learjet 
``Softflight'' configuration.
    These proposed requirements are the same actions currently required 
by AD 85-16-06.
    The applicability of the proposed AD would include all Learjet 
Model 35 and 36 series airplanes modified in accordance with Raisbeck 
STC SA766NW that are not currently subject to AD 85-16-04.


[Note: The FAA's normal policy is that when an AD requires a 
substantive change, such as a change (expansion) in its 
applicability, the ``old'' AD is superseded by removing it from the 
system and a new AD is added. In the case of this proposed AD 
action, the FAA normally would have proposed superseding AD 85-16-04 
to expand its applicability to include the additional affected 
airplanes. However, in reconsideration of the entire fleet size that 
would be affected by a supersedure action, and the consequent 
workload associated with revising maintenance record entries, the 
FAA has determined that a less burdensome approach is to issue a 
separate AD applicable only to these additional airplanes. This 
proposed AD would not supersede AD 85-16-04; airplanes listed in the 
applicability of AD 85-16-04 are required to continue to comply with 
the requirements of that AD. This proposed AD is a separate AD 
action, and is applicable only to airplanes that are not subject to 
AD 85-16-04.]

Petitioning for an Exemption of the Requirements of the Final Rule

    Affected operators should note that the aileron instability that is 
the subject of this proposed AD is a condition affected by the contour 
of the wing leading edge, which is a function of manufacturing 
tolerances. In light of this, the FAA recognizes that not all airplanes 
modified in accordance with Raisbeck STC SA766NW may exhibit the 
problem of aileron buffet or buzz below .83 Mach. Should this proposal 
become a final rule, operators of those airplanes may wish to petition 
the FAA for an exemption from the requirements of the rule, under the 
provisions of part 11 of the Federal Aviation Regulations (14 CFR 11), 
``General Rulemaking Procedures.''
    Petitioners for such an exemption should provide data that would 
justify a grant of exemption, including, but not limited to, 
information concerning the number of flights the airplane has flown in 
conditions involving high weight, high altitude, and high speed, and if 
any incident of buffet or buzz was observed during flight in those 
conditions. Based on the data submitted with the petition, the FAA will 
determine on a case-by-case basis if a flight evaluation or other 
additional data are necessary to determine if granting the petition (1) 
would not adversely affect safety, and (2) would be in the public 
interest.

Cost Impact

    There are approximately 29 Gates Learjet Model 35 and 36 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that at least 1 airplane of U.S. registry would be affected 
by this proposed AD.
    To accomplish the removal and recalibration of the airspeed 
indicators and Mach overspeed warning switch, and to revise the AFM 
Supplement, as would be required by ``Option I'' of the proposed rule, 
it would take approximately 5 work hours per airplane, at an average 
labor rate of $60 per work hour. The FAA estimates that it would cost 
approximately $1,000 per airplane to reset the airspeed indicators and 
Mach overspeed warning switch. Based on these figures, the cost impact 
of this action of the proposed AD on U.S. operators is estimated to be 
$1,300 per airplane.
    To accomplish the removal of the STC modifications, as would be 
required by ``Option II'' of the proposed rule, it would take 
approximately 100 work hours per airplane, at an average labor rate of 
$60 per work hour. Based on these figures, the cost impact of this 
action of the proposed AD on U.S. operators is estimated to be $6,000 
per airplane.
    The cost impact figures discussed above are 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.

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

[[Page 21984]]

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 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Gates Learjet: Docket 96-NM-63-AD.

    Applicability: Model 35, 35A, 36 and 36A series airplanes, 
modified in accordance with Raisbeck Group Supplemental type 
Certificate (STC) SA766NW, that do not have one of the serial 
numbers listed in Table 1 of this AD; certificated in any category.

                                 Table 1                                
               [Serial Numbers * NOT affected by this AD]               
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35-023...........        35A-092           35A-192-            36-004   
35-034-..........       35A-093-           35A-203-            36-017   
35-042-..........       35A-095-           35A-206-            36-028   
35-044-..........       35A-118-           35A-207-           36A-029   
35-047-..........       35A-127-           35A-209-           36A-031   
35A-068-.........       35A-132-           35A-228-           36A-038   
35A-073-.........       35A-135-           35A-231-           36A-043   
35A-075-.........       35A-145-           35A-244-           36A-044   
35A-076-.........       35A-172-           35A-245-                     
35A-086 -........       35A-185-            36-003                      
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*Airplanes having the serial numbers listed in Table 1 are subject to   
  similar requirements mandated by AD 85-16-04, amendment 39-5110.      

    Note 1: This AD applies to each airplane as indicated in the 
preceding applicability provision, regardless of whether it has been 
otherwise 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 (b) 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 prevent deterioration of the airplane's lateral control 
characteristics as a result of aileron buffet or buzz, accomplish 
the following:
    (a) Within 200 hours time-in-service after the effective date of 
this AD, or within 6 months after the effective date of this AD, 
whichever occurs first, accomplish either paragraph (a)(1) or (a)(2) 
of this AD:
    (1) Option I. Permanently reduce the airplane's maximum 
operating Mach limit (M<INF>MO) by accomplishing the actions 
specified in paragraphs (a)(1)(i), (a)(1)(ii), and (a)(1)(iii) of 
this AD:
    (i) Submit the FAA-approved STC SA766NW Airplane flight Manual 
Supplement to the Manager, Flight Test Branch, ANM-160S, Seattle 
Aircraft Certification Office, FAA, Transport Airplane Directorate, 
1601 Lind Avenue SW., Renton, Washington 98055-4056; to change the 
limit Mach number from .83 to .80. And
    (ii) Remove the ``Mach Overspeed Warning Switch'' and have it 
reset from Mach .83 to .80. Contact the manufacturer, PRECISION 
SENSOR, P.O. Box 509, Milford, Connecticut 06460; telephone number 
(203) 877-2795; to have the instrument recalibrated. Reidentify the 
Mach overspeed warning switch by ink-stamping the words ``Mach limit 
.80'' adjacent to the part number. Reinstall the ``Mach Overspeed 
Warning Switch'' after it has been so recalibrated. And
    (iii) Remove the pilot's and copilot's airspeed indicators and 
have them modified by changing the ``barber pole'' from Mach number 
.83 to .80. The instrument must be recalibrated by the instrument 
manufacturer or a certified repair station. Reidentify the airspeed 
indicators by ink stamping ``Mach limit .80'' adjacent to the part 
number. Reinstall the pilot's and copilot's airspeed indicators 
after they have been so modified.
    (2) Option II. Remove the modifications installed in accordance 
with Raisbeck Group STC SA766NW, and return the aircraft either to 
the original type design configuration, or to the Gates Learjet 
``Softflight'' configuration.
    (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, Seattle Aircraft Certification 
Office (ACO), FAA, Transport Airplane Directorate. Operators shall 
submit their requests through an appropriate FAA Principal 
Maintenance Inspector, who may add comments and then send it to the 
Manager, Seattle ACO.

    Note 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (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 May 7, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-11881 Filed 5-10-96; 8:45 am]
BILLING CODE 4910-13-P