US investigators have determined that localised air turbulence damaged the elevator of a parked Boeing MD-83 to the extent that it jammed when the aircraft attempted to take off from a Michigan airport two years ago.
The crew of the Ameristar aircraft aborted the take-off after the jet failed to rotate during its departure from Willow Run airport, near Ypsilanti, on 8 March 2017.
National Transportation Safety Board analysis found that the aircraft had been parked on the ramp for two days close to a large hangar.
While the surface winds and gusts did not exceed aircraft design limits, computational fluid dynamics simulations showed the hangar’s presence generated localised turbulence with a vertical component that “rapidly” flipped the MD-83’s elevator surfaces up and down.
This caused the elevators – which, by design, did not have gust locks – to strike their mechanical stops, sufficiently hard to jam the right-hand elevator in a full trailing-edge down position, leaving the aircraft incapable of rotation during take-off.
Circumstances of the accident, says the inquiry, highlighted that Boeing’s safeguards “do not adequately protect” crews and passengers from the possibility that a free-floating elevator can become jammed before departure.
The NTSB says there is a “lack of a means” for crews to detect a jammed elevator during pre-flight checks on the type.
It says the crew had calculated the V1 decision speed as 139kt and rotation speed as 150kt. The call to rotate, from the monitoring pilot, came at 151kt airspeed but, while the left elevator moved 15° up the right elevator stayed 16° down.
The aircraft, which reached a maximum airspeed of 173kt, did not rotate and the captain aborted the take-off roll.
NTSB analysis found the jet had travelled 5,850ft along runway 23L before the crew applied brakes, leaving just 1,800ft of paved surface. It overran the paved surface at 100kt and struck a raised perimeter road at 40kt before coming to a halt.
Investigators credit the MD-83’s captain with a “timely and appropriate” decision to reject the take-off, and the monitoring pilot’s “disciplined adherence” to standard operating procedures after the captain’s decision to abort.
While the aircraft was substantially damaged, all 110 passengers and six crew members evacuated with only one passenger receiving minor injuries.
In the wake of the accident the inquiry has recommended that Boeing complete development of a modification for MD-80s – as well as the similar 717 – to prevent a possible elevator jam from wind exposure, and establish new pre-flight procedures to enable crews to verify that no jam has occurred.