[Federal Register Volume 61, Number 181 (Tuesday, September 17, 1996)]
[Rules and Regulations]
[Pages 48822-48824]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-23710]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-63-AD; Amendment 39-9759; AD 96-19-13]
RIN 2120-AA64


Airworthiness Directives; Gates Learjet Model 35 and 36 Series 
Airplanes Modified by Raisbeck Supplemental Type Certificate (STC) 
SA766NW

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
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 requires a reduction of the maximum 
operating limit speed on the affected airplanes to prevent encountering 
certain potentially hazardous conditions. This amendment is prompted by 
reports of incidents of aileron buffet or buzz experienced during high 
speed cruise. The actions specified by this 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.

EFFECTIVE DATE: October 22, 1996.

ADDRESSES: Information concerning the subject of this rule may be 
obtained from Jet Air Corporation, P.O. Box 245, Bellevue, Washington 
98009. Information concerning this rulemaking action may be examined at 
the Federal Aviation Administration (FAA), Transport Airplane 
Directorate, Rules Docket, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT: 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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Gates Learjet Model 35 and 
36 series airplanes that have been modified in accordance with Raisbeck 
Supplemental Type Certificate (STC) SA766NW was published in the 
Federal Register on May 13, 1996 (61 FR 21982). That action proposed to 
require a reduction of the maximum operating limit speed on the 
affected airplanes to prevent encountering certain potentially 
hazardous conditions.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the single comment received.

Request to Require New Part Numbers of Modified Parts

    One commenter requests that the proposal be revised to require 
that, once the overspeed warning switch is recalibrated and the 
airspeed indicators are modified [in accordance with OPTION I of the 
proposed AD], new part numbers should be assigned to those items. 
Additionally, the commenter requests that a parts catalog supplement be 
issued with the STC, calling out the correct new part number of the 
devices for future reference by maintenance personnel. The commenter 
considers that merely ink-stamping

[[Page 48823]]

these parts once the required actions have been accomplished on them, 
as the proposed rule specifies, is not generally acceptable practice. 
The commenter states that, if either of those items is replaced in the 
future, there is no mechanism in place that would prevent the 
installation of a standard (unmodified) part number device in the 
airplane. Therefore, the airplane would no longer be in compliance with 
the AD, and would not be airworthy.
    . The FAA does not concur with the commenters request for two 
reasons:
    1. First, assigning and changing part numbers, and developing a 
parts catalog supplement, would be more labor-intensive and time 
consuming than ink-stamping a recalibrated or modified part. 
Additionally, the FAA is not convinced that the actions suggested by 
the commenter would be any more effective than the requirements of this 
AD.
    2. Second, to show that actions specified in this AD have been 
complied with, it is necessary for the operator to make a maintenance 
log book entry indicating that the modified and ink-stamped warning 
switch and airspeed indicators are installed. If these items are 
replaced in the future (with parts that are not modified and not ink-
stamped), a review of the log book entry would readily inform the 
mechanic or inspector that the airplane is not in compliance with the 
AD. Further, this process for verifying compliance would be identical 
whether the part is ink-stamped or has a new part number.

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 as proposed.

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 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. 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 must 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 
would not adversely affect safety, and 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 will 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 provided by ``Option I'' of the proposed rule, it will 
take approximately 5 work hours per airplane, at an average labor rate 
of $60 per work hour. The FAA estimates that it will 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 
(Option 1 of the AD) on U.S. operators is estimated to be $1,300 per 
airplane.
    To accomplish the removal of the STC modifications, as provided by 
``Option II'' of the rule, it will 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 (Option II of the 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 requirements of this 
AD action, and that no operator would accomplish those actions in the 
future if this AD were not adopted.

Regulatory Impact

    The regulations adopted herein will not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) Is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) will not have a 
significant economic impact, positive or negative, on a substantial 
number of small entities under the criteria of the Regulatory 
Flexibility Act. A final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

Adoption of the Amendment

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

PART 39--AIRWORTHINESS DIRECTIVES

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

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


Sec. 39.13  [Amended]

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

96-19-13 Gates Learjet: Amendment 39-9759. Docket 96-NM-63-AD.

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

            Table 1.--Serial Numbers* NOT affected by this AD           
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            ................
                                                                        
*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

[[Page 48824]]

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) (``OPTION 
I'') or (a)(2) (``OPTION II'') of this AD:
    (1) OPTION I. Permanently reduce the airplane's maximum 
operating Mach limit (MMO) 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 Mach .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 
recalibrated 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 Mach number .80. The instrument must be recalibrated by the 
instrument manufacturer or a certified repair station. Reidentify 
the modified 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.
    (d) This amendment becomes effective on October 22, 1996.

    Issued in Renton, Washington, on September 10, 1996.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-23710 Filed 9-16-96; 8:45 am]
BILLING CODE 4910-13-U