AD 96-19-13

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AD Number:
96-19-13
Document Type:
AD Final Rules
Docket Number:
96-NM-63-AD
Subject Heading:
Airworthiness Directives; Gates Learjet Model 35 and 36 Series Airplanes Modified by Raisbeck Supple...Show more
Subject:
Operating Mach Limit
Status:
Current
Citation:
Federal Register: September 17, 1996 (Volume 61, Number 181)
Citation Publish Date:
09/17/1996
Effective Date:
10/22/1996
Make:
Learjet Inc.
Model:
35 | 35A (C-21A) | 36 | 36A
Product Type:
Aircraft
Product Subtype:
Small/Large Airplane
Affected AD:
Superseded AD:
Affected By:
Superseded By:
Service/Office:
Office of Primary Responsibility:
CFR Part Reference:
Part 39 [61 FR 48822 NO. 181 09/17/96]
Comments:
AIRWORTHINESS DIRECTIVES FINAL RULES: 96-19-13
CITATION:   [Federal Register: September 17, 1996 (Volume 61, Number 181)]

PAGE NUMBER:   [Page 48822]

DOCKET NUMBER:   96-NM-63-AD

AMENDMENT:   39-9759

AD NUMBER:   96-19-13

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

ACTION:   Final rule

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.

DATES:   Effective 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 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 commenter’s 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.

§ 39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive:

REGULATORY TEXT:  
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 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.

FOOTER: