China Airlines Disputes Official Finding of Pilot Error

Air Safety Week, Feb 14, 2005

Carrier Says Evidence Points to Wind Shear in MD-11 Crash

China Airlines (CAL) is refusing to accept the official government conclusion that pilot error caused the crash of an MD-11 B-150 at Hong Kong's new Chek Lap Kok Airport (CLC) on Aug. 22, 1999. Instead, the carrier claims there is new factual information proving that wind shear or a "microburst" at the last moment caused the aircraft to land hard, flip over and kill three on board.

The Hong Kong Civil Aviation Department (HKCAD) is stubbornly sticking to its report's "pilot error" bottom line. The accident was caused by "the commander's inability to arrest the high rate of descent," the HKCAD report says. It was almost guaranteed that the pilot, Italian expatriate Gerrardo Lettich, would have to take the fall for an error of judgment for placing his aircraft in jeopardy, but there were significant other factors in play. One of these -- monsoonal wind conditions -- relates to the overall safety of Chek Lap Kok in severe weather conditions, according to the Taiwan Aviation Safety Council (ASC). More on this below.

On the day of the accident, there was a severe tropical storm in the vicinity and strong winds and severe turbulence was forecast. China Airlines Flight 642's highly experienced captain "lost it," according to the report, in the last 50 feet of his stable approach and landed hard enough to break the right wing's landing gear, lose the right wing, roll inverted and somersault through 180--. The aircraft came to a final stop upside-down alongside the runway and facing in the direction of the approach. The accident killed three people and seriously injured 50 of the 300 passengers and crew on board. The quick reaction of airport firefighters to extinguish the blaze before it engulfed those trapped in the wreckage saved hundreds of lives. It took nearly three hours for rescue workers to extract all the survivors.

Aircraft serviceability was not deemed to be a factor so the accident had to be attributed to the pilot's decision-making, handling and use of systems in the severe weather conditions. Of 26 approaches flown in the period of three and three-quarter hours up to the accident, 10 resulted in go-rounds as a result of the high winds. The only other MD-11/DC-10 to arrive in the period of deteriorating weather landed 3.5 hours earlier than Flight 642.

Prevailing visibility and braking action weren't factors, and the commander's crosswind technique wasn't faulted. The aircraft was not fitted with the optional rain repellent system, however, the commander's assessment of visibility through his windshield on final approach was "moderate." Despite that assessment, it is possible that sunset, overcast conditions, and rainwater on the windshields outside the sweep of the windshield wipers and on the unswept side-windows, may have affected his peripheral vision; this may have resulted in him not appreciating the aircraft's developing high rate of descent as it passed the normal flare height.

The right side landing gear broke because of a very late-developing high descent rate and a slight 4-- right wing down touchdown. The investigation therefore concentrated on airspeeds and wind profiling. The MD-11's Quick Access Recorder (QAR) buffers data and writes it every 35 seconds. If power is lost, as it was here, that final critical accident data is not written and is lost. The flight data recorder (FDR) similarly had a defective longitudinal accelerometer input so the wind profiling had to be "reconstructed" from the four touchdown zone anemometers. Boeing [BA] did two studies of the wind affecting the final approach, one in 2000 and another in 2003 (after the earlier one was found to have been mathematically flawed). The National Transportation Safety Board (NTSB) agreed with the method but never checked either sets of figures.

The Boeing conclusion was that there had been a 20-knot loss in airspeed in the last 50 feet of the approach. Part of that could be attributable to windshear or loss of headwind, Boeing said, and part to the scheduled closure of the throttles by the auto-throttle (A/T) system at 50-feet radio altitude (RA). Simply put, the pilot had cancelled the autopilot-flown instrument landing system (ILS) upon becoming visual with the runway lights at 700 feet but in accordance with company SOP (standard operating procedure), he'd left the autothrottles active. According to other MD-11 pilots, that might be SOP but it was also his fatal error. The Flight 642 pilots had determined the landing reference speed (Vref) as 152 knots, and selected a target approach speed of 170 knots in view of the expected strong wind and turbulence on final approach.

The HKCAD report states:

"The auto-throttle controlled the speed adequately within a four or five knot tolerance either side of a mean speed of 165 kt until just below 300 ft RA [radio altitude] when the indicated airspeed fell to 157 kt. The co-pilot called 'Speed' and claimed to have moved the thrust levers forward when there was no apparent response from the commander; however, in a later statement the commander claimed that he had moved the thrust levers forward. The thrust then increased significantly from a previous average of 1.05 EPR [computed engine pressure ratio] to almost 1.3 EPR, with a consequential increase in speed to 175 kt. The A/T [auto-throttle] response to this excessive speed was to put the thrust levers at the fully closed position by about 70 ft RA, and the thrust decayed to an average of 1.0 EPR by 50 ft RA (the altitude at which the autothrottle would've otherwise normally commenced a thrust lever retard), and to idle thrust by 35 ft AGL."