Flight Controls Control Column Section

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FAA Aviation Safety SPECIAL AIRWORTHINESS INFORMATION BULLETIN SUBJ: Flight Controls – Control Column Section SAIB: NM-13-38 Date: June 24, 2013 This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) informs owners, operators, and maintenance personnel of Learjet Inc. Model 23 24, 24A, 24B, 24B-A, 24C, 24D, 24D-A, 24E, 24F, 24F-A, 25, 25A, 25B, 25C, 25D, 25F, 28, 29, 31, 31A, 35, 35A (C-21A), 36, and 36A airplanes of an airworthiness concern regarding possible cracking in the control column of the flight controls.

At this time, the airworthiness concern is not an unsafe condition that would warrant Airworthiness Directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) Part 39.

Background

Maintenance personnel reported finding cracks in the control column on Learjet Model 35A (C-21A) airplanes. Five airplanes were inspected and all five had cracks in the same general area. The cracks all originated at the base of the column where it attaches to the floor structure. The bearing boss where a pivot pin is installed was partially cracked in all cases. This detail is typical for both the left- hand and right-hand sides of the control column. Investigation of the cracking on these airplanes by both Learjet and FAA personnel revealed that a portion of the bearing boss was cracked, and the pivot pin remained intact with no jamming of the control system.

Learjet has issued the following Service Bulletins for the affected airplanes:

• SB 23/24/25-27-12 Revision 2, dated October 26, 2009. • SB 23/24/25-27-24, dated December 17, 2012. • SB 28/29-27-29, dated December 17, 2012. • SB 31-27-33, dated December 17, 2012. • SB 35/36-27-48, dated December 17, 2012.

The service bulletins specify inspecting the control column for cracks and replacing the control column assembly, including repair reinforcement of the bearing boss which supports the pivot pin.

Recommendations

The FAA recommends that all owners and operators of the Learjet airplanes identified above follow the actions outlined in the above service information, at the earliest opportunity.

For Further Information Contact

Paul Chapman, Aerospace Engineer, Airframe and Services Branch, ACE-118W, FAA, Wichita Aircraft Certification Office; 1801 Airport Road, Room 100, Mid-continent Airport, Wichita, Kansas 67209; phone: 316 946-4152; fax: 316 946-4129; email: [email protected].

2 (Optional) For Related Service Information Contact

Learjet, Inc., One Learjet Way, Wichita, KS 67209-2942; telephone 316-946-2000; fax 316-946-2220; email [email protected]; Internet http://www.bombardier.com.