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[Federal Register Volume 60, Number 94 (Tuesday, May 16, 1995)]
[Proposed Rules]
[Pages 26003-26004]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-11975]

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Proposed Rules
                                                Federal Register
________________________________________________________________________

This section of the FEDERAL REGISTER contains notices to the public of 
the proposed issuance of rules and regulations. The purpose of these 
notices is to give interested persons an opportunity to participate in 
the rule making prior to the adoption of the final rules.

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Federal Register / Vol. 60, No. 94 / Tuesday, May 16, 1995 / Proposed 
Rules

[[Page 26003]]

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 95-NM-25-AD]

Airworthiness Directives; Learjet Model 35, 35A, 36, 36A, 55, 
55B, and 55C 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 certain Learjet Model 35, 35A, 36, 
36A, 55, 55B, and 55C airplanes. This proposal would require 
installation of a placard on the instrument panel in the cockpit to 
advise the flightcrew that the Omega navigation system may be 
inoperative at certain engine speeds. This proposal is prompted by 
reports of loss of certain navigation signals during extended over 
water operation. The actions specified by the proposed AD are intended 
to prevent excessive deviation from the intended flight path due to 
loss of navigation signals, which could result in a potentially low-
fuel condition or a traffic conflict.

DATES: Comments must be received by June 26, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 95-NM-25-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9 a.m. and 3 p.m., Monday through Friday, except Federal 
holidays.
    The service information referenced in the proposed rule may be 
obtained from Gates Learjet, Mid-Continent Airport, P.O. Box 7707, 
Wichita, Kansas 67277. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: C. Dale Bleakney, Aerospace Engineer, 
ACE-130W, Systems and Equipment Branch, FAA, Wichita Aircraft 
Certification Office, Small Airplane Directorate, 1801 Airport Road, 
Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 
946-4135; fax (316) 946-4407.

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 95-NM-25-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. 95-NM-25-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports of loss of the Omega navigation signal 
from certain global navigation systems (GNS) manufactured by Flight 
Management Systems and installed on various Learjet airplane models. 
These systems, GNS-500, GNS-1000, and GNS-X, have been shown to be 
susceptible to generator noise at approximately 92.5% N2. This 
generator noise has the potential to render the Omega navigation signal 
inoperative. GNS-500, GNS-1000, and GNS-X systems all rely on a single 
Omega frequency of 13.6 KHz. This is the same frequency as the noise 
created by the Bendix generator used on Model 35, 36, and 55 airplanes 
when operated near 92.5% N2. If alternate suitable navigation 
signals such as VOR, VOR/DME, GPS, and VLF, are deselected and the GNS-
500, -1000, or -X system is used exclusively, the aircraft may enter a 
``dead reckoning'' mode until a suitable navigation signal is obtained. 
Use of the GNS-500, -1000, or -X navigation system exclusively during 
extended overwater operation with the Omega signal rendered inoperative 
due to generator noise, could result in excessive deviation from the 
intended flight path, and may lead to a potential low-fuel condition or 
a traffic conflict.
    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 installation of a placard on the instrument 
panel in the cockpit to advise the flightcrew that the Omega navigation 
system may be inoperative when engine speed reaches 92.5% N2.
    Additionally, the FAA has reviewed and approved Gates Learjet 
Airplane Accessory Kit Model 55 AAK 55-85-2 (for Model 55 airplanes) 
dated January 14, 1986, as revised by Airplane Accessory Kit Change 
Notice AAK No. AAK55-85-2, Change 1 (undated). The FAA has also 
reviewed and approved Gates Learjet Airplane Accessory Kit Model AAK 
85-1, dated January 14, 1986 (for the Model 35 and 36 airplanes), as 
revised by Airplane Accessory Kit Change Notice AAK-85-1, Change 1 
(undated).
    These kits describe procedures for installation of a generator band 
reject filter on certain Model 35, 36, and 55 series airplanes. This 
noise filter will prevent generator noise from reaching the 13.6 KHz 
frequency.
    This proposed AD also would provide operators with the option of 
installing the applicable modification as [[Page 26004]] terminating 
action for the required placard.
    As a result of recent communications with the Air Transport 
Association (ATA) of America, the FAA has learned that, in general, 
some operators may misunderstand the legal effect of AD's on airplanes 
that are identified in the applicability provision of the AD, but that 
have been altered or repaired in the area addressed by the AD. The FAA 
points out that all airplanes identified in the applicability provision 
of an AD are legally subject to the AD. If an airplane has been altered 
or repaired in the affected area in such a way as to affect compliance 
with the AD, the owner or operator is required to obtain FAA approval 
for an alternative method of compliance with the AD, in accordance with 
the paragraph of each AD that provides for such approvals. A note has 
been included in this notice to clarify this long-standing requirement.
    There are approximately 710 Learjet Model 35, 35A, 36, 36A, 55, 
55B, and 55C airplanes of the affected design in the worldwide fleet. 
The FAA estimates that 177 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. The cost of required parts (local 
manufacture of a placard) is negligible. Based on these figures, the 
total cost impact of the proposed AD on U.S. operators is estimated to 
be $10,620, or $60 per airplane.
    Should an operator elect to accomplish the optional terminating 
action that would be provided by this AD action, it would take 
approximately 14 work hours to accomplish it, at an average labor rate 
of $60 per work hour. The cost of required parts would be approximately 
$3,050 per airplane. Based on these figures, the total cost impact of 
the optional terminating action would be $3,890 per airplane.
    The total 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.
    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 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 
106(g); and 14 CFR 11.89.

Sec. 39.13  [Amended] -

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

Learjet: Docket 95-NM-25-AD.

    Applicability: Model 35, 35A, 36, 36A, 55, 55B, and 55C 
airplanes; equipped with Global Wulfsburg GNS 500, GNS-1000, and 
GNS-X Flight Management Systems; 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 (d) 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 prevent excessive deviation from the intended flight path 
which, if the aircraft is on an extended overwater operation, may 
lead to a potential low-fuel condition or a traffic conflict 
operation, accomplish the following:
    (a) Within 60 days after the effective date of this AD, install 
a placard in a prominent location on the instrument panel that 
states:

``VLF/OMEGA MAY BE INOPERATIVE AT 92.5% N2''

    (b) For Model 35 airplanes, serial numbers 35-001 through 35-603 
inclusive; and Model 36, serial numbers 36-001 through 36-053 
inclusive: Installation of a GNS 500/1000 generator band reject 
filter in accordance with Gates Learjet Airplane Accessory Kit Model 
AAK 85-1, dated January 14, 1986, as revised by Airplane Accessory 
Kit Change Notice AAK-85-1, Change 1 (undated), constitutes 
terminating action for the placard requirement of paragraph (a) of 
this AD. Following installation of the filter, the placard required 
by paragraph (a) of this AD may be removed.
    (c) For Model 55 airplanes, serial numbers 55-003 through 55-124 
inclusive: Installation of a GNS 500/1000 generator band reject 
filter in accordance with Gates Learjet Airplane Accessory Kit Model 
55 AAK 55-85-2, dated January 14, 1986, as revised by Airplane 
Accessory Kit Change Notice AAK No. AAK55-85-2, Change 1 (undated), 
constitutes terminating action for the placard requirement of 
paragraph (a) of this AD. Following installation of the filter, the 
placard required by paragraph (a) of this AD may be removed.
    (d) 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, Wichita Aircraft Certification 
Office (ACO), FAA, Small 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, Wichita ACO.

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

    (e) 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 10, 1995.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-11975 Filed 5-15-95; 8:45 am]
BILLING CODE 4910-13-U
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