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'Slip slidin' away'

Borrowing a title from songwriter Paul Simon, aircraft seat design would seem to be a well-established discipline, honed after decades of experience to a fine art—but apparently it is not.

Photo by Chris Rose.

If you haven’t been keeping up with the news recently, and I wouldn’t blame you for missing this, a Boeing 787 had a midflight 500-foot negative altitude excursion described by the airline as a “technical incident.” Unbelted passengers and possibly some cabin staff were plastered against the overhead with quite a few injuries. This incident is in preliminary investigation status, so stay tuned to learn more.

The theory at this point is that a seat adjustment rocker switch located on the seat back was inadvertently bumped by a flight attendant while bringing food to the flight deck. This caused the electric seat to motor forward and push the pilot into the controls causing the “technical incident.” Could it have been anticipated? Hindsight would say “of course,” but unlikely events are tough to foresee. Boeing has put out a safety advisory.

Leaving the arcane design of air carrier flight decks behind, there’s a much more likely problem in the light general aviation fleet. The humble seat gets used and abused, especially in rental and flight school aircraft. The seat tracks, pins, holes, rollers, and other components wear out. There have been a few crashes and incidents resulting from poor maintenance.

Generally, the seat slides aft, leaving pilots out of touch with the flight controls. The FAA has published several airworthiness directives on seats, including one I found as recently as 2011. It covers most, if not all, Cessna singles and several of the company’s twins. An easy fix was to put a hard stop on the seat track to keep the seat from sliding off the end of the track and was inexpensive to implement. Commenters to the FAA’s AD thought that should be sufficient, but the Feds noted that vertically challenged pilots still might not be able to reach the controls. Rails, holes, locking pins, and rollers needed to be replaced on condition and inspected regularly. (Not easy to replace a hole so I guess that means the rails!)

It’s not always the old designs that have issues. A Cirrus SR22 crashed on takeoff when the pilot’s seat slid aft to the secondary stop because the locking pins were only partially engaged. The NTSB determined the pilot failed to properly secure his seat before takeoff, resulting in loss of control when he couldn’t reach the rudder pedals. This was the pilot’s third SR22 and he was 69 inches tall, for the record. In nearly 800 hours of flying SR22s he’d never had a problem with the seats before.

The NTSB noted, “During post-accident functional testing of the seat, when twisting forces to the right were applied to the seat and while being slid forward, the seat position locking pin could be partially engaged, but not all the pins would seat, and the control handle would not go fully down, nor could it be forced into position. Straightening or forward movement of the seat resulted in full pin engagement with the control handle in the fully down position (emphasis added.) Given this information, it is likely that the pilot applied a twisting force when moving the seat and did not fully engage the seat position locking pins before initiating the takeoff.” Note that this appears to be a one-off incident.

In the early days, before the Cessna ADs, I reminded my solo Cessna 150 students that if the seat slipped during takeoff, which seats were known to do, to not grab the control yoke but rather reach for the door post and pull themselves back to a normal position. I’d personally and inadvertently tested that procedure during a takeoff, and it worked well. This typically would happen at the worst possible time: just after liftoff as the aircraft was pitching up. The pilot’s weight shifted more onto the seat back, thus lifting the locking pin out of the slot. Having this happen in a Cessna 172 was more problematic because of the greater cabin area, but the door post could still usually be reached.

When one thinks about all the things that could go wrong in aviation, seats don’t make the top 10 list, but the outcomes can be just as serious. One final thought: If you’re flying a legacy, classic (old) aircraft that does not yet have shoulder harnesses, please make that the very next upgrade—soon. The NTSB still goes to otherwise survivable crashes only to find that shoulder harnesses would have made all the difference. Please remain seated and keep that seatbelt fastened.

ASI Staff
Bruce Landsberg
Senior Safety Advisor

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