[Federal Register Volume 64, Number 94 (Monday, May 17, 1999)]
[Proposed Rules]
[Pages 26703-26705]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-12298]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-372-AD]
RIN 2120-AA64


Airworthiness Directives; Learjet Model 23, 24, 25, 28, 29, 31, 
55, and 60 Series 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 23, 24, 25, 
28, 29, 31, 55, and 60 series airplanes. This proposal would require a 
one-time detailed visual inspection of the electrical wire leads of the 
horizontal stabilizer anti-ice system to verify that the numbers on the 
wire leads correctly correspond to the numbers on the connected 
airframe wiring; installation of a wire ID strap on the left- and 
right-hand sides of each terminal block; and installation of a warning 
placard. This proposal is prompted by a report of severe flight control 
buffeting of a Learjet Model 55 series airplane due to a malfunction of 
the horizontal stabilizer anti-ice system. The actions specified by the 
proposed AD are intended to prevent undetected accretion of ice on the 
leading edge of the horizontal stabilizer, which could result in the 
loss of pitch control and consequent reduced controllability of the 
airplane.

DATES: Comments must be received by July 1, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-372-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.
    The service information referenced in the proposed rule may be 
obtained from Learjet, Inc., One Learjet Way, Wichita, Kansas 67209-
2942. This information may be examined at the FAA, Transport Airplane 
Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, 
Small Airplane Directorate, Wichita Aircraft Certification Office, 1801 
Airport Road, Room 100, Mid-Continent Airport, Wichita, Kansas.

FOR FURTHER INFORMATION CONTACT: Jose Flores, Senior Aerospace 
Engineer, Systems and Propulsion Branch, ACE-116W, FAA, Small Airplane 
Directorate, Wichita Aircraft Certification Office, 1801 Airport Road, 
Room 100, Mid-Continent Airport, Wichita, Kansas 67209; telephone (316) 
946-4133; 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 98-NM-372-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-114, Attention: Rules 
Docket No. 98-NM-372-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

[[Page 26704]]

Discussion

    The FAA has received a report indicating that a Learjet Model 55 
series airplane declared an emergency during flight due to severe 
flight control buffeting; the airplane landed safely. Following a 
detailed visual inspection of the horizontal stabilizer anti-ice 
system, it was determined that the wiring on two terminal strips was 
incorrectly connected, which caused electrical heating elements of the 
anti-ice system to operate out of sequence and allowed ice to build up 
on the horizontal stabilizer. When operating correctly, the center 
electrical heating element is provided with continuous electrical 
power. Incorrect wiring can cause the center element to cycle on and 
off and, subsequently, the anti-ice system will not function properly, 
which can cause the ice to build up on the leading edge of the 
horizontal stabilizer. Further investigation revealed that during 
routine maintenance of the airplane's anti-ice system, the wire numbers 
connecting the airplane wiring through two terminal strips were 
incorrectly matched to the electrical heating elements in the leading 
edge, which led to miswiring of the connection. This condition, if not 
corrected, could result in undetected accretion of ice on the leading 
edge of the horizontal stabilizer, and consequent loss of pitch control 
and reduced controllability of the airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Learjet Service Bulletins SB 23/
24/25-30-3, (for Model 23, 24, and 25 series airplanes), SB 28/29-30-3 
(for Model 28 and 29 series airplanes), SB 31-30-05 (for Model 31 
series airplanes), SB 55-30-3 (for Model 55 series airplanes), and SB 
60-30-4 (for Model 60 series airplanes); all dated October 27, 1998; 
which describe procedures for a one-time detailed visual inspection of 
the electrical wire leads of the horizontal stabilizer anti-ice system 
to verify that the numbers on the wire leads correctly correspond to 
the numbers on the connected airframe wiring; installation of a wire ID 
strap on the left- and right-hand sides of each terminal block; and 
installation of a warning placard. The new placard will provide clear 
and visible warning that reads: ``WARNING--PROPER CONNECTION OF BOOT 
WIRING IS CRITICAL, REFER TO WIRING/SERVICE MANUAL.'' Accomplishment of 
the actions specified in the service bulletins is intended to 
adequately address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

    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 accomplishment of the actions specified in 
the service bulletins described previously, except as discussed below.

Differences Between Proposed Rule and Service Bulletins

    Operators should note that, although the service bulletins 
recommend accomplishing the detailed visual inspection and 
installations within 300 flight hours (after the release of the service 
bulletin), the FAA has determined that a compliance time of 300 flight 
hours would not address the identified unsafe condition in a timely 
manner. In developing an appropriate compliance time for this proposed 
AD, the FAA considered not only the manufacturer's recommendation, but 
the degree of urgency associated with addressing the subject unsafe 
condition, the average utilization of the affected fleet, and the time 
necessary to perform the inspection and installations (one work hour). 
In light of all of these factors, the FAA finds a 100-flight-hour 
compliance time for initiating the required actions to be warranted, in 
that it represents an appropriate interval of time allowable for 
affected airplanes to continue to operate without compromising safety.

Cost Impact

    There are approximately 1,010 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 806 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 
inspection and installations, and that the average labor rate is $60 
per work hour. Required parts would be provided by the manufacturer at 
no cost to the operators. Based on these figures, the cost impact of 
the proposed AD on U.S. operators is estimated to be $48,360, or $60 
per airplane.
    The 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.

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 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:

Learjet: Docket 98-NM-372-AD.

    Applicability: Model 23, 24, 25, 28, 29, 31, 55, and 60 series 
airplanes; as listed in Learjet Service Bulletins SB 23/24/25-30-3, 
SB 28/29-30-3, SB 31-30-05, SB 55-30-3, and SB 60-30-4, all dated 
October 27, 1998; 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 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

[[Page 26705]]

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 undetected accretion of ice on the leading edge of 
the horizontal stabilizer, which could result in the loss of pitch 
control and consequent reduced controllability of the airplane, 
accomplish the following:

One-Time Inspection

    (a) Within 100 flight hours after the effective date of this AD: 
Perform a one-time detailed visual inspection of the electrical wire 
leads of the horizontal stabilizer anti-ice system to verify that 
the numbers on the wire leads correctly correspond to the numbers on 
the connected airframe wiring, in accordance with Learjet Service 
Bulletins SB 23/24/25-30-3, (for Model 23, 24, and 25 series 
airplanes), SB 28/29-30-3 (for Model 28 and 29 series airplanes), SB 
31-30-05 (for Model 31 series airplanes), SB 55-30-3 (for Model 55 
series airplanes), or SB 60-30-4 (for Model 60 series airplanes); 
all dated October 27, 1998; as applicable.

    Note 2: For the purposes of this AD, a detailed inspection is 
defined as: ``An intensive visual examination of a specific 
structural area, system, installation or assembly to detect damage, 
failure or irregularity. Available lighting is normally supplemented 
with a direct source of good lighting at intensity deemed 
appropriate by the inspector. Inspection aids such as mirror, 
magnifying lenses, etc. may be used. Surface cleaning and elaborate 
access procedures may be required.''

Corrective Action

    (1) If no discrepancy is detected during the inspection required 
by paragraph (a) of this AD: Concurrent with the inspection, install 
a wire ID strap on the left- and right-hand sides of each terminal 
block, and install a warning placard on each terminal block, in 
accordance with the applicable service bulletin.
    (2) If any discrepancy is detected during the inspection 
required by paragraph (a) of this AD: Prior to further flight, 
repair the discrepancy in accordance with the procedures specified 
in Chapter 30 of the Learjet Airplane Wiring Manual. Concurrent with 
the repair, install a wire ID strap on the left- and right-hand 
sides of each terminal block, and install a warning placard on each 
terminal block; in accordance with the applicable service bulletin.

Alternative Methods of Compliance

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

Special Flight Permits

    (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 10, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-12298 Filed 5-14-99; 8:45 am]
BILLING CODE 4910-13-P