Airborne Express Flight 827

Investigation

The National Transportation Safety Board (NTSB) launched an investigation into the accident and arrived at the crash site the same day. Both flight recorders were recovered the next morning. Rescue teams also recovered all six bodies. Efforts to reach the accident site were initially hampered due to its remote location.

The aircraft's flight controls were destroyed in the crash, but the NTSB recovered two trim jackscrews from the horizontal stabilizer.

The NTSB recreated the stall in a simulator. In the simulation, the stick shaker activated at 144 kn. Despite deepening the stall, no unexpected nose-down pitches or lateral rolls occurred in the simulator. The decreasing airspeed caused the nose to pitch up.

In 1991, another Airborne Express DC-8 had entered a real stall during an FEF, but the flight crew was able to recover and test continued with no further incidents. In the 1991 incident, the stick-shaker activated the same time the buffeting sensation occurred. The Federal Aviation Administration (FAA) issued a revised stall recovery procedure to Airborne Express, which they agreed to incorporate. However, the airline had only partially incorporated the procedure at the time of the Flight 827 accident.

Airborne Express' flight operation manual contained only a short section labeled "Test Flights" and the requirements for FEF's read:

At the time of the accident, there were scattered showers of light rain and the cloud ceiling was between 14000 ft and 15000 ft. The reported surface weather at Mercer County Airport in Bluefield stated that visibility was two miles.

Because of the aircraft experiencing icing, it experienced a buffet 12 kn before the stall speed. The FDR indicated that the aircraft had entered a real stall at 126 kn, four knots before the stall speed. The NTSB concluding that the icing, regardless of amount, (along with flight control rigging) did not contribute to the accident.

Despite Captain Lemming's timely decision to terminate the stall test, he subsequently pulled back on the control column from five to ten degrees, allowing the aircraft to enter a real stall. The NTSB notes that he likely did this in an attempt to establish an appropriate pitch attitude and power setting.

Captain Avery did not notice the incorrect flight control inputs made by Captain Lemming, though he did attempt to instruct Lemming on how to recover the airplane from the roll, but not how to recover from the stall. In addition he did not enhance his instructions or take over control of the aircraft himself. The NTSB noted that since both pilots were captains, had manager positions at the airline, and had similar backgrounds, they would have difficulty challenging each other because of a lack of command authority. Captain Avery, as PIC, should have monitored and challenged captain Lemming's actions, but both his PIC and instructional roles were informal on the accident flight.

According to both flight recorders and the recovered horizontal stabilizer trim jackscrew, Captain Lemming had trimmed the aircraft's horizontal stabilizer at 175 kn instead of the intended 184 kn. Airborne Express' procedures required the aircraft to be trimmed 1.5 kn before the stall speed. Despite the incorrect trim setting, the aircraft would still have been recoverable from the stall. The NTSB concluded that Captain Lemming's incorrect trimming of the horizontal stabilizer was not a factor in the accident.

The NTSB examined N827AX's maintenance records and reviewed Airborne Express' procedures for testing the stall warning system, but could not determine why the stick shaker was inoperative during the accident flight. In addition, the flight crew's situational awareness that the aircraft was in a stall was short, as they were distracted by the compressor stall on the no. 2 engine and communications with ATC. The NTSB also stated that an angle of attack display on the flight deck could have helped the crew's situational awareness. The fact that the crew lacked a visual horizon at nighttime was another factor due to the aircraft being in instrument meteorological conditions (IMC) from the time the stall maneuver was performed until impact.

Neither Captain Avery nor Captain Lemming had ever flown a DC-8 post modification on an FEF until December 21 (the initial FEF that was aborted), though the director of flight technical programs authorized Avery to serve as a pilot in command on post modification FEF's.

Final report

The NTSB released the final report on July 15, 1997. The "probable cause" section stated the following:

The accident had been caused by pilot error due to captain Lemming's improper flight control inputs and captain Avery's failure to notice them. Another cause was Airborne Express failing to set up a proper program for FEFs, resulting in inadequate training. Contributing factors included the stick shaker being inoperative, inaccuracies in Airborne Express' flight simulators when simulating a stall, the compressor stall on the no. 2 engine which distracted the flight crew, the accident occurring at night (which resulted in the flight crew's lack of a visual horizon and other exterior cues), and Airborne Express not requiring flight tests to be completed before nightfall.