On 22 December 1996, during a post-maintenance airworthiness function flight at night Instrument Meteorological Conditions (IMC), a Douglas DC8-60 being operated by Airborne Express failed to recover from an intentional approach to the stall and a full stall and loss of control without recovery then followed and led to impact into mountainous terrain in the vicinity of Narrows, Virginia.
The following is an extract from the National Transportation Safety Board (USA) (NTSB) Report on the Accident:
"FAA National Track Analysis Program (NTAP) data indicate that the airplane climbed through 9,000 feet at 1743:08. The airplane was level at 14,100 feet at 1745:50 and remained within 300 feet of that altitude until 1808:18, just before it entered a steep descent, according to NTAP data. Upper air temperature and dew point data indicated that cloud tops were just below 14,000 feet along the airplane’s route of flight. Flight crew comments recorded on the cockpit voice recorder (CVR) indicated that the airplane flew briefly in and out of the clouds and that ice buildup was observed after they reached their assigned block altitude." […]
The official NTSB Report states:
"FDR data indicated that the EPRs (Engine Pressure Ratio) on all engines were at or near idle power as the airplane slowed to stall speed for the stall test maneuver and EPRs were increased by about 0.05 about 11 seconds before the pre-stall buffet was called. FDR data showed that at the time of impact, engine EPR levels were at or near idle. The full range of motion of the airplane’s control column position (CCP) was about 37 degrees (5 degrees forward of neutral and 32 degrees aft of neutral). During the last 2 minutes of flight, the CCP peaked, at times, at 32 degrees aft, according to FDR data. A Safety Board performance study based on FDR data indicated that the pre-stall buffet began at 149 knots and that the stall occurred at 126 knots.
FDR data indicated that immediately after the PF commanded and applied power to recover from the stall (at 1808:13), all four engines accelerated, although the No. 2 engine accelerated to a slightly lower EPR than the other engines during the power increase. The engines had stabilized at maximum EPR by 1808:18. At 1808:20, the airspeed was decaying from 130 kts and the CVR recorded sounds similar to engine compressor surges (popping sounds) that continued for 9 seconds. During the period of engine compressor surges (at 1808:25), the FDR recorded EPR reductions. The power was subsequently increased two additional times before the airplane impacted terrain, but the CVR recorded no further sounds linked to engine compressor surges.
According to FDR data, at 1807:40, just before entering the stall sequence, the airplane’s airspeed was diminishing from 180 kts. The airspeed had decreased to 126 knots at 1808:11. Between that time and 1809:20, the indicated airspeed fluctuated rapidly and significantly, consistent with erratic airspeed indications. The airplane impacted terrain at more than 240 knots."
Causes and Recommendations
"The National Transportation Safety Board determines that the probable causes of this accident were the inappropriate control inputs applied by the flying pilot during a stall recovery attempt, the failure of the non-flying pilot-in-command to recognize, address, and correct these inappropriate control inputs, and the failure of ABX (Airborne Express) to establish a formal functional evaluation flight program that included adequate program guidelines, requirements and pilot training for performance of these flights. Contributing to the causes of the accident were the inoperative stick shaker stall warning system and the ABX DC-8 flight training simulator’s inadequate fidelity in reproducing the airplane’s stall characteristics.
Safety issues discussed in this report include airplane stall recovery procedures for functional evaluation flights, stall warning systems, fidelity of the ABX DC-8 flight training simulator, guidelines and limitations for conducting functional evaluation flights, and Federal Aviation Administration surveillance of air carrier functional evaluation flight programs.
Recommendations concerning these issues were made to the Federal Aviation Administration. In addition, the Safety Board restates a previous Safety Recommendation (A-96-94) to the FAA, which in turn should:
- Require that all transport-category aircraft present pilots with angle of attack information in a visual format, and that all air carriers train their pilots to use the information to obtain maximum possible climb performance."