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The discussion is an examination of the history of the flight and discussion on those findings I found were most causal to the accident that were covered by the National Transportation Safety Board during their investigation. The report also explores those probable causes that attributed to the accident and action provided by the National Transportation Safety board in the prevention of similar mishaps. On December 22, 1996, at 1810 eastern standard time, a Douglas DC-8-63, N827AX, operated by ABX Air Inc. (Airborne Express) impacted mountainous terrain in the vicinity of Narrows, Virginia, while on a post-modification functional evaluation flight. The three flightcrew members and three maintenance/avionics technicians on board were fatally injured. The airplane was destroyed by the impact and a postcrash fire. The functional evaluation flight, which originated from Piedmont Triad International Airport, Greensboro, North Carolina, was conducted on an instrument flight rules flight plan and operated under Title 14 Code of Federal Regulations Part 91. The National Transportation Safety Board determined 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 nonflying pilot-in-command to recognize, address, and correct these inappropriate control inputs, and the failure of ABX 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. In all the National Transportation Safety Board concluded there were twenty-three findings that directly contributed to this airplane accident. I will address the ones I feel carried the most impact where if the instance was removed the accident would have been prevented or the severity of it lessened. Starting with finding number 4. Some combination of airframe icing, flight control rigging, or other factors resulted in the greater-than-expected buffet onset speed; however, any effects of airframe icing or flight control rigging upon the stall speed of the accident airplane were minimal. Because the airplane had been operating at least intermittently in the cloud tops and below freezing air temperatures there was no definitive way to tell if this was a leading cause to the accident. Current weather conditions at that time were conducive to light-to-moderate icing for a brief period before the attempted stall maneuver. The aircrew's statements on the CVR (cockpit voice recorder) indicate they were aware of icing before starting the maneuver. The CVR also recorded comments indicating the airplane departed from the icing conditions sometime shortly after entering. The buffet and stall speeds also could have been affected by the rigging of the airplane’s flap and aileron control surfaces. These control surfaces had been re-rigged prior to FEFs (functional evaluation flights) on December 21 and 22, 1996, as a routine part of the overhaul of the mishap aircraft. Part of the FEF stall series checks verifies that control surface rigging was proper by comparing calculated stick shaker activation and stall speeds to the airspeeds at which the airplane actually encountered these events. Consequently, like airframe icing, variations in flap and aileron rigging could have caused the airplane to buffet at a greater airspeed than expected. The Safety Board was unable to determine the extent to which these possible conditions individually contributed to the early onset of buffet, but concludes that some combination of airframe icing, flight control rigging, or other factors resulted in the greater-than-expected buffet onset speed. No other data related to these items leads to any other conclusions. 7. The pilot not flying, as the pilot-in-command, failed to recognize, address and correct the pilot flying’s inappropriate control inputs. Both pilots were qualified to act as a DC-8 captain at ABX. CVR recordings and flight crew experience indicated the pilot not flying (PNF) the airplane was acting as the pilot-in-command (PIC). During the attempted stall recovery, there were several indications of the pilot flyings (PF) excessive aft control column inputs that should have suggested to the PNF that, as the PIC, he needed to correct the control inputs and recover from the stall. Because both pilots were captains, both were managers, and both had similar backgrounds at ABX, it may be difficult for one captain to challenge the actions of the other because of a lack of overt command authority. The PNF acted more as an instructor giving mild, informal verbal instructions while trying to talk the PF into inputting the proper control inputs to recover the airplane rather than taking over the controls himself. This "teaching" continued until the aircraft impacted the ground. This finding was listed as causal and I fully agree. 9. The inoperative stall warning system failed to reinforce to the flightcrew the indications that the airplane was in a full stall during the recovery attempt. The stall warning system stick shaker failed to activate during the accident sequence at the appropriate margin above the stall and during the full stall that followed. Although it did not hamper the initial identification of the stall, the absence of a stick shaker warning may have been confusing for the flightcrew. The pilots’ training and experience would have made them expect a stick shaker cue during the period the airplane was in a stalled condition. They were trained to respond to the stick shaker by adding power and reducing control column back pressure until the stick shaker ceased. If the flightcrew had received the expected cues from the stick shaker as the airplane subsequently was flown farther into the stall, the PF may have responded with more aggressive stall recovery actions, and the PNF would have received a stronger signal to intervene. It is also possible the aircrew, during the stall recovery effort, gradually lost the perception that the airplane was stalled and may have been attempting to perform a high airspeed, nose-low unusual attitude recovery. In either instance this system being inoperative directly contributed to the accident by failing to reinforce to the flightcrew the indications that the airplane was in a full stall during the recovery attempt. 10. This accident might have been prevented if the flightcrew had been provided a clear, direct indication of the airplane’s angle of attack. The flight crew did not have a display of the airplanes angle of attack. This instrumen-tation would have provided a direct indication of the pitch attitudes required for recovery throughout the attempted stall recovery sequence. Without it the pilot has to rely on numerous other indicators to give him readings on the airplanes angle of attack which may or may not give him the correct indications. In response to another airplane accident, the FAA is currently evaluating the operational requirements for angle of attack instrumentation on transport-category aircraft. The Safety Board reiterates the recom-mendation it put forth before and I concur. 12. The flightcrew did not have a clearly visible natural horizon because of darkness and clouds above and below the airplane, and the airplane most likely encountered instrument meteorological conditions soon after descending through 13,500 feet and remained in instrument meteorological conditions until just before impacting terrain. The accident airplane was in VMC (visual meteorological conditions) above a cloud layer when the flightcrew began the stall series. However, based on weather satellite data and almanac information, the Safety Board concluded that the flightcrew did not have a clearly visible natural horizon because of darkness and clouds above and below the airplane, and that the airplane most likely encountered IMC (instrument meteorological conditions) soon after descending through 13,500 feet and remained in IMC until just before impacting terrain. Because they were in minimum clearance from the clouds as soon as they initiated the stall maneuver, the flight crew was forced to rely on instrument references for the stall recovery. Although equipped with a electronic flight instrument (EFIS) display which displays an artificial horizon, the Safety Board, believes and I concur, the natural horizon may have provided a more rapid orientation for the flightcrew and prevented this accident. 14. The flightcrew’s exposure to a low fidelity reproduction of the DC-8’s stall characteristics in the ABX DC-8 flight training simulator was a factor in the pilot flying holding aft (stall-inducing) control column inputs when the airplane began to pitch down and roll. In the ABX DC-8 simulator, when slowed to below the airspeed of stick shaker activation, the simulator developed a stable, nose-high, wings-level descent, with no tendency to pitch down in a stall break. In contrast, according to Douglas and ABX manuals and the FDR data from the accident flight, the actual DC-8 airplane’s stall characteristics include a pronounced stall break. Further, after slowing well below stall speed, the simulator entered a mode in which the aerodynamic buffet stopped and the airspeed did not continue to decrease. This was clearly not the fidelity level to which to aircrew should have trained. Moreover, the PF and PNF the airplane were exposed to extensive DC-8 simulator experience to what they presumed was the stall behavior of the DC-8. So when they experienced a different stall break in the airplane, it surprised them. The PF responded with what he had been trained but unfortunately in the airplane his control inputs didn't work. 15. The accident could have been prevented if ABX had institutionalized and the flightcrew had used the revised functional evaluation flight stall recovery procedure agreed upon by ABX in 1991. On May 16, 1991 another ABX DC-8 experienced an in-flight loss of control during an FEF while recovering from a stall. The maneuver was begun at 13,000 feet and the flightcrew recovered at 7,000 feet. The PIC of the incident flight was the DC-8 flight standards manager at the time. As a follow-up to this incident, the FAA (Federal Aviation Administration) and ABX agreed flightcrews would fly the FEF profile in the simulator before the actual evaluation flight; airborne maneuvers would be executed in an ATC-assigned altitude block depth ranging from 3,000 feet to 5,000 feet. Recovery was to be accomplished with pitch (lowering the nose), and power then slowly advanced to complete the recovery. The revised FEF stall recovery procedure stressed a positive reduction of pitch attitude to rapidly decrease the angle of attack below the critical stall angle before the application of engine power. In calling for a more positive reduction of pitch attitude, the revised procedure eliminated the emphasis of the standard ABX stall recovery procedure on minimum altitude loss. The principal operations inspector (POI) from the Federal Aviation Administration (FAA) recalled that at some time following the 1991 incident the director of flight technical programs had voiced disagreement about the need to change the FEF stall recovery procedures. The director of flight technical programs continued to use the old stall recovery procedures and was eventually put in charge as a fllight standards manager. In this position he trained the accident PNF, who in turn, trained the accident PF. The Safety Board notes that although some provisions of the revised procedure were used, the manner in which they were used confirmed that the flightcrew was attempting the original, minimum altitude loss stall recovery. This ultimately resulted in incorrect procedures being used to recover from a stall maneuver. 16. ABX’s failure to require completion of a functional evaluation flight by sundown or to establish adequate limitations on ambient lighting and weather conditions led the flightcrew to attempt the stall series in the absence of a natural horizon. ABX had weather minimums for FEF takeoffs but no minimums were established for maneuvers performed at higher altitudes and beyond the vicinity of the airport, such as the stall series. Further ABX guidance for performing the clean stall maneuver specified a minimum altitude of 10,000 feet agl and a maximum altitude of 15,000 feet msl. However, no requirements were established for ambient lighting conditions, visual references, or distance from cloud tops. This direction, or lack there of, went further into management by the director of flight technical programs stating to Safety Board Investigators that he preferred the stall series not to be performed in IMC. In contrast, subsequent Safety Board investigation of flight manuals from two other air carriers restricted stall series maneuvers to being performed in VMC with a visible horizon. Manuals of two airplane manufacturers limited the stall maneuver to daylight hours. The lack of guidance by ABX management put the aircrew into a position where they, unknowingly, made a bad decision that ultimately cost them their life. 20. The flightcrew’s decision to conduct the flight at night was influenced by the succession of delays they had experienced earlier in the day. The Safety Board looked into whether the flightcrew’s decision to fly the FEF at night was prompted by supervisory or self-imposed pressure. Although being close to Christmas Day and the crewmembers all being TDY to Greensboro NC from their homes in Wilmington OH, this was found not to be a factor. However the completion of the modifications to the accident airplane had been delayed for several months. This had caused the marketing managers to inform a freight charter customer expecting delivery of this airplane that its charters were subject to cancellation on short notice. The Safety Board was unable to identify the accident flightcrew’s state of awareness of plans for the accident airplane, but because both the PF and the PNF were managers at ABX they should have been aware of the company’s desire to place the airplane in revenue service as soon as possible. They then most likely would have responded with a strong effort to get the job done. Having experienced a succession of delays for maintenance from a scheduled departure of 1320 hours, it may have been more difficult for them to reverse their decision to perform the flight. The NTSB determined the probable causes of the accident were the inappropriate control inputs applied by the flying pilot during a stall recovery attempt, the failure of the nonflying pilot-in-command to recognize, address, and correct these inappropriate control inputs and the failure of ABX 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 airplanes stall characteristics. Recommendations include requiring the Douglas Aircraft Company change maintenance and calibration requirements for all DC-8 stall warning systems, improving the fidelity of the simulators in reproducing the stall characteristics of the airplanes they represent, ensure ABX incorporates the revised functional evaluation stall recovery procedure in its FEF program and developing an advisory circular advising aircrew on correct stall maneuver procedures. Additional requirements were for the FAA to identify operations that require special consideration and require special training and operational guidance. They were also to take a more active role in surveillance of FEF programs for air carriers and modify current operating instructions to clarify airworthiness and operational procedural requirements for conducting FEF’s in transport-category aircraft. The Safety Board also reiterated its standing recommendation to present pilots with angle-of-attack information in a visual format and to train them to use the information to obtain maximum possible climb performance. Bibliography: National Transportation Safety Board, Aircraft Accident Report NTSB/AAR-97/05 Word Count: 2652
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