Airworthiness Directives; Learjet Model 23, 24, 25, 28, 29, 31, 55, and 60 Series Airplanes

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