Sunday, October 14, 2012

Cessna 152 - Seat Movement

        A recent occurrence report concerned a Cessna 152 whose pilot, among other problems, reported that his seat was loose in flight. Loose seats are a not unusual subject of incident reports and the consequences of a pilot’s seat sliding back on take-off have been highlighted in previous GASIL articles.
           There are several possible reasons for a pilot’s seat to move. Incorrect locking should be avoided if the pilot confirms before take-off that his seat is properly locked. Some systems require (whether by design or sheer old age) the pilot to manually lift the locking bolt
and refit it to secure the seat. However, light aircraft seat rails and their floor attachments are very susceptible to damage. If a crack has formed across a locking hole in the seat rail, flexing may allow the locking bolt to come out of its hole. Careful inspection during maintenance is an important defence against such cracks growing and causing loss of control. Pushing one’s feet hard against the rudder pedals may be considered a practical method of checking seat
security. Unfortunately, damage to the rudder pedal mountings has resulted in the past from the
application of excessive force in this way. Damage to the seat locking mechanism itself can also be caused by over-zealously checking the seat’s security. We need to strike a balance between checking security and risking damage.

                 FAA AD, 2011-10-09 on  Cessna Seat Rail/Locking Pin AD applicable for 
 Cessna 150, 152, 170, 172, 175, 177, 180, 182, 185, 188, 190, 195, 206, 207, 210, T303, 336, and 337 series airplanes concerning the wear of the seat attachment rails and the associated hardware that ensures the pilot and copilot’s seats are firmly mounted and locked in position. The new AD retains all the actions of the original one issued in 1990, with added steps to the inspection procedures, added revised figures, and clarification of some of the existing steps.

         The FAA issued the AD “to prevent seat slippage or the seat roller housing from departing the seat rail, which may consequently cause the pilot/copilot to be unable to reach all the controls. This failure could lead to the pilot/copilot losing control of the airplane.”

              The time interval for the AD remains at 100 hours. Some commenters had asked that the requirement be based on an annual basis; the FAA declined to make the change, stating the wear of the seat retention components was based on their belief that “the unsafe condition of excessive wear results from usage, not calendar time. The more an airplane is used, the more likely wear will develop, causing an unsafe condition.”
          FAA AD, 2011-10-09 supersedes AD 87-20-03 R2, Amendment 39-6669.

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