China Airlines Flight 006
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 Damaged empennage of N4522V
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| Summary | |
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| Date | February 19, 1985 |
| Type | No. 4 engine failure, crew error, crew fatigue, jet lag |
| Site | Over the Pacific Ocean near San Francisco, U.S.A. |
| Passengers | 251 |
| Crew | 23 |
| Injuries | 2 |
| Fatalities | 0 |
| Survivors | 274 (all) |
| Aircraft type | Boeing 747SP-09 |
| Operator | China Airlines |
| Tail number | N4522V |
China Airlines Flight 006 (callsign "Dynasty 006") was a daily non-stop flight departing from Taipei at 10:15 am and arriving in Los Angeles International Airport at 7:00 Am local time. On February 19, 1985, it was involved in an incident that caused two serious injuries and substantial damage to the aircraft. After ten hours of flight the Boeing 747SP-09 lost power in one of its four engines. In spite of having several minutes to act, the pilots failed to adjust the controls to counteract the asymmetric thrust resulting from the failed engine. The aircraft eventually rolled over and plunged 30,000 ft (9,100 m), experiencing high speeds and very high forces. The pilots recovered control and diverted to San Francisco International Airport.
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[edit] The incident
The incident involving this Boeing 747SP occurred some ten hours into its regular Taipei-Los Angeles service, 350 miles (550 kilometers) to the northwest of San Francisco, cruising at an altitude of 41,000 ft (12,500 m).
The flight crew consisted of Min-Yuan Ho, the pilot, Ju Yu Chang, the copilot, and Kuo-Win Pei, the flight engineer. Augmentees included Chien-Yuan Liao, captain, and Shih Lung Su, flight engineer.[1]
The 747SP suffered an engine failure on one of its four powerplants after encountering jetstream turbulence. Improper emergency procedures were executed by the flight crew leading to a loss of flight control.
During the encounter with jetstream-related turbulence, generally termed clear-air turbulence, the airplane's airspeed began to fluctuate causing the digital engine control systems to fluctuate the fuel supply (governing engine thrust output) in compensation. The outboard starboard engine (engine number four) failed to accelerate when commanded, becoming hung in a low power condition. The Flight Engineer was unable to contain the engine's unstable performance and after 90 seconds it flamed out (providing no thrust). It is possible the Flight Engineer neglected to shut a bleed air valve in accordance with normal procedures.
Being aware of the engine failure the Captain instructed the engineer to initiate the restart procedure. To ensure an adequate probability of success Boeing recommends that in-flight engine restart attempts should be executed below an altitude of 30,000 feet (9,100 m). Contrary to standard operating procedures insufficient rudder control input was provided while, in addition, the autopilot systems remained engaged. The autopilot systems subsequently issued roll commands to the ailerons in an attempt to counter the yaw associated with an engine failure. Owing to the aerodynamic properties of this configuration increased amounts of drag were experienced, leading to a decay in airspeed. Without the benefit of sufficient roll authority the autopilot system was unable to prevent the eventual roll to starboard. The resulting uncontrolled flight path is depicted below.
Noticing the decrease of airspeed (a certain quantity of which is necessary to maintain level flight) the Captain programmed the autopilot system to descend the aircraft, a basic manoeuver allowing the conversion of altitude into speed thus guarding against the possibility of a stall. Nevertheless the airspeed continued to decay prompting the decision to disengage the autopilot system. The earlier failure of the flight crew to apply manual rudder control input and the subsequent full roll authority commanded by the autopilot system meant that upon reversion of flight control to the flight crew an unexpectedly high manual roll input was required to maintain the present flight condition. The flight crew had not expected the need to apply large manual input forces and, as a result of the decreased port roll command, the aeroplane began a roll to starboard. The Captain's attention was drawn to the artificial horizon since it showed a vertical horizon which was also displayed by the First Officer's instrument, thus ruling out the possibility of an instrument failure. At this point the aeroplane was inside clouds, preventing visual cues for orientation. The aeroplane entered a steep dive at a high bank angle. Altitude decreased 10,000 ft (3,000 m) within only twenty seconds. The crew and passengers experienced G forces reaching as much as five G.
Only after breaking through the bottom of the clouds at 11,000 feet (3,400 m) could the captain orient himself and bring the plane under control, leveling out at 9,600 feet (2,900 m). They had descended 30,000 ft (9,100 m) in under two and a half minutes. The flight crew were under the impression that all four engines had flamed out, but the National Transportation Safety Board believes only engine No. 4 had quit. After leveling out the three good engines were giving normal power and a restart attempt brought No. 4 back into use. They began climbing and reported to air traffic control "condition normal now" and they were continuing on to Los Angeles. They then noticed that the landing gear were down and one of the plane's hydraulic systems was empty. Because they didn't have fuel to reach Los Angeles with the drag added by the landing gear, they diverted to San Francisco. Learning there were injured people on board, an emergency was declared and they flew straight in to the airport and landed without further incident to the plane and passengers.
[edit] The aftermath
There were two injuries. One was a fracture and laceration of a foot; the other acute back strain requiring two days of hospitalization. The aircraft was significantly damaged by the aerodynamic forces. The wings were permanently bent upwards by two inches, and the landing gear and nearby airframe had much damage. Most affected was the tail, where large outer parts of both horizontal stabilizers had been ripped off. The entire left outboard elevator had been lost along with its actuator, which had been powered by the hydraulic system that ruptured and drained. The landing gear doors flew off the plane during a plunge.
After substantial investigation, this incident brought to international attention the problem of jet lag as a contributing factor to pilot errors. The captain was considered to be highly experienced and had flown six international flights in the previous two weeks. Though he testified that he did not believe he was tired, NTSB investigators suggest that his inability to sleep during his rest period and the fact that the incident took place at 2 a.m. Taipei time contributed to his inability to focus on and process important details about the aircraft's behavior that could have averted the incident.
As of February 1, 2007, the aircraft involved in this incident is now reportedly for sale. [1]
[edit] Footnotes
- ^ "China Airlines Boeing 747-SP Accident Report"
- ^ NTSB report courtesy of University of Bielefeld - Faculty of technology html version by Hiroshi Sogame Safety Promotion Comt. All Nippon Airways
[edit] External links
- Accident Brief by the U.S. National Transportation Safety Board
- Full Accident Report by the U.S. National Transportation Safety Board
- Summary and comments in Risks Digest
- Time Magazine story
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