On October 19, 2021, at about 10:00 am central daylight time, a Boeing MD-87, N987AK, operated by 987 Investments LLC, overran the departure end of runway 36 at Houston Executive Airport (TME), Brookshire, Texas, after the crew executed a rejected takeoff. Of the 23 passengers and crew onboard the airplane, two passengers received serious injuries and one received minor injuries. A postcrash fire ensued, and the airplane was destroyed. The airplane was operating as a 14 Code of Federal Regulation Part 91 flight from TME to Laurence G. Hanscom Field Airport (BED), Boston, Massachusetts.
Upon notification, the NTSB launched a go-team led by an investigator-in-charge and specialists in systems, structures, powerplants, operations, human performance, survival factors, air traffic control (ATC), maintenance records, and recorders. Parties to the investigation include the Federal Aviation Administration (FAA), The Boeing Company, Pratt &Whitney, and Everts Air Cargo. Numerous local law enforcement and public safety agencies also assisted with the initial response.
The following groups have been formed to investigate this accident: airplane systems, flight crew operations, human performance, survival factors, powerplants, maintenance records, weather, flight data recorder (FDR) and cockpit voice recorder (CVR). Additional groups may be formed as the investigation progresses.
Before the flight, the first officer conducted a preflight of the airplane while the captain obtained the flight plan paperwork and weather. The airplane departed at approximately 10:00 CDT from runway 36 at the Houston Executive Airport (TME). The captain was the pilot flying, and the first officer was the pilot monitoring.
According to flight crew interviews, during the takeoff roll, the first officer made the 80-knot, V1, and Vr callouts. At the rotate callout, the captain tried to pull back on the control column but indicated that it felt like it was “in concrete.” About the time the first officer made the V2 callout, the captain informed the first officer of the problem. The first officer also attempted to pull back on the control column but was unable to pull it aft. The first officer called abort and retarded the thrust levers, and the captain deployed the thrust reversers. The captain indicated that the autobrake system was in rejected takeoff (RTO) mode, and it applied maximum wheel braking.
The airplane overran the end of the runway, went through the airport’s perimeter fence, through power lines and came to rest in a field adjacent to the airport about 1,400 feet from the end of the runway. The captain commanded the first officer to “get out” and the first officer exited the flight deck to assist with the passenger evacuation. The flight crew indicated that they confirmed that all passengers were off the airplane before they exited the airplane.
The airplane came to rest about 1,400 feet from the end of the runway on a heading of about 235º. No parts of the airplane were found on the runway or prior to the airport perimeter fence. Pieces of the airplane were found in the field between the perimeter fence and the main wreckage. Initial examination of the airplane by investigators found that the airplane structure forward of the empennage was heavily damaged due to the postcrash fire that ensued after the airplane came to rest. All of the upper fuselage structure (except for a small section of the upper nose structure and empennage) was consumed by fire.
Both engines remained attached to their respective engine mounts, which were still connected to the empennage of the airplane and were in their normal orientation. There was no evidence of uncontainment and both thrust reversers were intact and in their fully closed position. An exhaust pattern of burned earth and singed grass, approximately 90 feet long was observed behind the exhaust duct of the right hand (No.2) engine, consistent with engine operation while stationary, after the airplane came to rest. The left hand (No.1) engine displayed no stationary exhaust pattern on the ground, however, onsite examination revealed that the fuel control unit (FCU) mounting flange to the high-pressure fuel pump was fractured with the surfaces displaying overload features. Additionally, the FCU housing exhibited overload fractures near the fuel metering valve housing cavity.
The airplane is a t-tail design, such that the elevators and horizontal stabilizer are attached near the top of the vertical stabilizer about 30 feet above ground level (agl). The left and right elevators are attached by hinges to the rear spar of the horizontal stabilizer, and each was equipped with control, geared, and antifloat tabs attached to the trailing edge (see figure 2). Each elevator can travel between 27° trailing edge up (TEU) and 16.5° trailing edge down (TED) between mechanical stops mounted on the horizontal stabilizer. (A stop arm on each elevator contacts the mechanical stops to limit elevator travel, and a torsion bar distributes any increased loading.)
When the airplane is parked, each elevator is free to move independently within the confines of its mechanical stops if acted upon by an external force, such as wind or manipulation by maintenance personnel. The elevator system (by design) has no gust lock, and the elevators are not interconnected.
Figure 2 exemplar airplane elevators and tabs
Initial examination of the elevator control system by investigators found that most of the system components forward of the engines had been consumed by the postcrash fire; therefore, full flight control continuity could not be established. However, the airplane’s empennage/tail section was not consumed by the postcrash fire and both the left and right elevators were found in a trailing edge down position (see figures 3 and 4).
Figure 3(left) View of the tail section of the airplane and Figure 4 (right) View of the left stabilizer and elevator.
Using a lift to access the elevators, investigators found that the airplane’s left and right elevators were jammed in a TED position and could not be moved when manipulated by hand. Both inboard actuating cranks for both elevator’s geared tabs were bent outboard, and their respective links were bent (see figures 5) Further, both actuating cranks and links were found locked in an overcenter position beyond their normal range of travel. The elevators, horizontal stabilizer, and control tabs have been retained by the NTSB for further examination.
Figure 5 View of the left and right elevator geared tab links and actuating crank
Investigators recovered the flight data recorder (FDR) and cockpit voice recorder (CVR) from the wreckage and transported them to the NTSB’s Vehicle Recorder Lab in Washington, DC. The airplane was equipped with a Honeywell solid state CVR and a Honeywell tape FDR. Both recorders exhibited signs of external thermal damage. The CVR’s internal medium was generally intact, however, the FDR’s internal medium exhibited signs of damage. Both recorders were downloaded using laboratory techniques.
Preliminary data from the airplane’s FDR showed that both elevators were positioned at approximately 18º to 19º trailing edge down when the flight crew applied power and remained there during taxi. Upon reaching rotation speed, the recorded elevator positions split, but neither moved to a trailing edge up position. The airplane reached a maximum speed of about 158 knots before decelerating. The operating parameters appeared normal on both engines and matched throughout the recording.
The CVR audio contained about 31 minutes of audio. The sound quality was generally poor but the boarding of passengers through the accident sequence was captured. Select checklist items could be heard and the takeoff ground roll sounded uneventful through the V1, rotate, and V2 callouts. An abort callout was then heard, followed by sounds consistent with the airplane departing the runway. The recording ended shortly thereafter, before the evacuation began. A CVR group comprised of technical experts will be convened at the NTSB’s Vehicle Recorder Lab to produce a transcript.
The damage observed to the left and right elevator geared tab input rod links is similar to the damage found during an investigation of a Boeing MD-83, which crashed after a rejected takeoff on March 8, 2017. The final report can be found on the investigation webpage.
Additional information will be released as warranted.