Cracked Control Columns On Lear 35A Airplanes Prompt The Action

The FAA has issued a Special Airworthiness Information Bulletin (SAIB) for several models of Learjet after 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 SAIB is directed to 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

According to the FAA, 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 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.

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.

FMI: SAIB, www.bombardier.com