Deja Vú as Jammed Elevators Found Again

The NTSB issued an update into the October 19 incident at Houston Executive Airport involving an MD-87 that overran the runway following a rejected takeoff. New information may have confirmed some concerns about the elevator linkage, with reports that the actuating cranks for the elevator's geared tabs were bent outboard, with their links bent. Both the actuating cranks and links were found locked in an overcenter position beyond their normal range of travel. The similarity in the tail jamming phenomenon has been noted to a similar MD-83 rejected takeoff and elevator jam that occurred in 2017. 

The charter flight was leaving Texas for Boston after being taken out of 10 months’ storage before the accident. Prior to takeoff, the elevators on both sides were jammed in a down position, unresponsive even after rotation speed was reached. The aircraft reached a maximum speed of 158 knots before the crew began decelerating. The aircraft continued past the end of the runway, catching on power lines and fenceline before coming to rest. The passengers were able to clear the plane in time, with only minor injuries, before a significant fire consumed the majority of the aircraft. The NTSB states that the tail was left mostly intact, a fortunate turn for evaluating the cause of the accident. 

The elevators were found to be jammed with their trailing edge down, somewhat similar to a 2017 accident in Ypsilanti, Michigan involving an MD-83. In that case, a takeoff was rejected, as well as an elevator jammed, with similar inspection results. In that case, extensive wind simulations found that the aircraft type had been originally certified for a ground gust limit load around 52 knots, later revised to 65 knots in 1997.

Similarly, the actuating mechanism of the right elevator had been forced beyond its normal range and become locked in an overcenter position. This was later attributed to eddy flows, gusts, and turbulence incurred while taxiing that exceeded the limit of the control linkages. Elevators on MD-83 are primarily moved indirectly by action of the control column on the control tabs, with no direct link between the movement of the column and elevator position, leading the final report in that incident to bemoan the difficulty in assessing elevator movement in the pre-takeoff "Free and Clear' control checks. Additionally, the aircraft lacked built-in gust locks for parked protection, leaving crews with little method to evaluate functionality until they get to speed. 

Further developments are expected, with more lessons learned from the incident. Owners and operators of MD-series aircraft may note with interest the recommendations of the 2019 final report of the previous overrun incident, and beware of the possible effects of ground gusts on elevator function.

FMI: www.ntsb.gov