Jammed elevators due to high wind prior to flight caused the crash during take-off of a Boeing MD-87 near Houston in October 2021, marking another instance of a known hazard.
That is according to the National Transportation Safety Board (NTSB), which says failures by the company that employed the private jet’s pilots contributed to the accident.
All 23 people aboard the MD-87 survived, though two were seriously injured. The aircraft was destroyed.
The crash resulted from “the jammed condition of both elevators, which resulted from exposure to localised, dynamic high wind while the airplane was parked, and prevented the airplane from rotating during the take-off roll”, says the NTSB in its accident report, released on 28 September.
“The possibility of elevator jamming on DC-9/MD-80 series airplanes as a result of exposure to certain high-wind conditions while parked is known and evidenced by two previous events – a rejected take-off event in 1999 in Germany and a runway overrun accident in 2017 in Ypsilanti, Michigan,” the report adds.
It also says the pilots of the MD-87 that crashed in 2021 were unaware of a requirement that they visually confirm, prior to flight, that the elevators were not jammed. That requirement stemmed from the Ypsilanti incident.
The NTSB faults the pilots’ employer, Alaska’s Everts Air, for not ensuring the pilots were informed, saying Everts failed “to maintain awareness of Boeing-issued, required updates for its manuals”.
Cargo carrier Everts did not respond to a request for comment.
A private firm called 987 Investments owned the MD-87 (registration N987AK) and hired Everts to supply pilots and to provide a maintenance manager with “items due for the airplane, such as periodic inspections and airworthiness directives”, the NTSB says. The aircraft was operated under general aviation Part 91 rules.
The accident occurred during take-off from Houston Executive airport at 10:00 local time on 19 October 2021. The MD-87 accelerated normally but the captain told investigators that when he pulled back the control column “nothing happened”, saying it felt like it “was in concrete”.
Soon after, the first officer called “abort”, pulled the thrust levers to idle and braked as the captain deployed the thrust reversers, the NTSB says. The jet overran the runway, went through a perimeter fence, crossed a road, struck electric lines and trees, came to rest in a pasture and caught fire.
“Examination of the elevators and a review of [flight recorder] data for elevator position determined that both elevators were jammed trailing-edge-down, which prevented the airplane from rotating during the take-off roll,” the NTSB says.
Prior to the attempted take-off the MD-87 had been subjected twice to storms with winds of about 45kt (83km/h), though the NTSB says wind speeds could have been faster.
That wind likely caused the elevators’ linkages to move beyond their normal range, jamming the surfaces, the report says.
It notes that pilots cannot detect the jam through normal pre-flight flight-control checks, which the pilots of the MD-87 completed. “The elevator control system design is such that, even with this type of jammed elevator condition, the control column feel and travel would be normal during taxi.”
In response to the similar 2017 incident in Ypsilanti, Boeing in 2020, at the NTSB’s recommendation, issued a bulletin calling on MD-80-series operators to update flight crew manuals with a requirement that pilots visually confirm that the elevators are not jammed. Pilots must see that the elevators are even with the stabiliser surface.
“A review of Everts’… activity data showed no evidence that any Everts personnel had viewed or downloaded the bulletin before the accident,” says the NTSB. The pilots told the agency they were unaware of the procedure.