Jammed flight control led to aborted takeoff, accident report findsDavid Wagman | March 08, 2019
An MD-83 airplane ran off the end of the runway during a rejected takeoff in March 2017 because of an undetected mechanical malfunction. The National Transportation Safety Board (NTSB) released its finding in a recent report.
According to investigators, seconds after reaching the "takeoff decision" airspeed of 158 mph at about 5,000 feet down a 7,500-foot runway in Ypsilanti, Michigan, the captain’s attempt to raise the nose was unsuccessful and he called “abort.”
The airplane slowed following the rejected takeoff but was traveling too fast to stop on the remaining runway. It ran off the end of the runway at about 115 mph, traveled 950 feet across a runway safety area, struck an airport fence and stopped after crossing a paved road.
Investigators determined that a component of the elevator flight control system had jammed in the days before the accident flight while the aircraft was parked at the same airport during a wind storm with recorded gusts in excess of 60 mph.
The flight control system was designed and certified to withstand such horizontal gusts, but NTSB computer simulation of the wind flow showed that a nearby hangar generated localized turbulence. The turbulence created a vertical component that could move the elevator rapidly up and down, ultimately causing it to jam.
On the day of the aborted takeoff, the flight crew completed all preflight checks, including a test of the flight controls. The NTSB report said the crew found no anomalies before initiating the takeoff roll.
Investigators said that the captain’s decision to abort the takeoff and the other crew member’s efforts to assist him had likely contributed to the survivability of an accident in which there were no serious injuries among the 110 passengers and six crew members. The Ameristar Charters Boeing MD-83, which was transporting the University of Michigan basketball team to Washington, D.C., was substantially damaged.
The NTSB also said that the 1,000 ft runway safety area – added to the airport during upgrades between 2006 and 2009 – likely contributed to the lack of serious injuries. In 1999, in response to an NTSB recommendation, the Federal Aviation Administration began a national program to add runway safety areas to many commercial airports.
NTSB said that a need exists for lower ground gust criteria for elevator physical inspections and operational checks by maintenance personnel for Boeing DC-9/MD-80 series and 717 model airplanes.
It said that the aircraft operating manual (AOM) contained what NTSB said was an "amplified normal checklist" for flight crews that included a caution that airplanes exposed to high sustained wind or gusts greater than 65 kts were susceptible to elevator damage and/or jamming.
The AOM specified that for any airplanes suspected of that kind of wind exposure, inspections and checks laid out in Ameristar’s aircraft maintenance manual for the Boeing MD-83 were required. The manual included a warning that the airplane must be parked headed into the wind if gusts were expected to exceed 60 kts. It also cautioned that visual and physical inspections of all flight control surfaces were required if the airplane was subjected to wind exceeding 65 kts.
NTSB said that none of the recorded or forecasted wind at the Ypsilanti airport exceeded those limits during the time that the airplane was parked on the ramp. The highest reported wind gust was 55 kts and the highest forecasted gust was 48 kts.
According to the NTSB report, on March 8, 2017, just before 3 pm eastern standard time, Ameristar Charters, flight 9363, a Boeing MD-83 airplane, N786TW, overran the departure end of runway 23L at Willow Run Airport (YIP), Ypsilanti, Michigan.
The passengers and flight crew members evacuated the airplane via emergency escape slides. One slide failed to inflate and could not be used. One passenger received a minor injury, and the airplane sustained substantial damage. The airplane was destined for Washington Dulles International Airport, Dulles, Virginia. Visual flight rule conditions prevailed at YIP at the time of the accident.
During the takeoff roll, the captain, who was the pilot flying, executed the rejected takeoff 12 seconds after the airplane achieved V1 (takeoff decision speed) because he perceived that the airplane did not respond normally when he pulled back on the control column to command rotation.
Data from the airplane’s flight data recorder (FDR) showed that the airplane’s right elevator was positioned full trailing edge down (TED) when the flight crew first powered up the airplane. It remained there throughout the accident sequence. An airplane performance study confirmed that the airplane did not respond in pitch when the captain pulled on the control column. Based on the study’s comparison with a previous takeoff, the NTSB determined that the airplane’s lack of rotational response to the control column input did not become apparent to the captain in time for him to have stopped the airplane on the runway.
Post-accident examination showed that the right elevator’s geared tab’s inboard actuating crank and links had moved beyond their normal range of travel and became locked over center. This effectively jammed the right elevator in what NTSB said was a full-TED position and rendered the airplane incapable of rotating during takeoff.
The speed of the surface wind and gusts at the airport did not exceed the airplane's certification design limit or maintenance inspection criteria. However, the NTSB determined the airflow at the airplane’s parked location was affected by the presence of a large hangar that generated localized turbulence with a vertical component that moved the elevator surfaces rapidly up and down. That movement resulted in impacts against the elevator mechanical stops, imposing dynamic loads sufficient to jam the right elevator.