Communiqués

TSB # A 14/96

 

(For release 18 October 1996)

(Hull, Quebec) - The Transportation Safety Board (TSB) has concluded its investigation into the rejected take-off and runway overrun accident at Vancouver International Airport on 19 October 1995. In its report, the Board has identified the safety deficiencies that contributed to this occurrence: an engine monitoring program that was not timely enough to correct an engine condition that contributed to a loss of power; and lack of knowledge regarding the characteristics of engine stalls, which contributed to the crew's misidentification of the cause of a loud bang.

Action has already been implemented by Canadian Airlines International (CAI), Transport Canada (TC), and McDonnell Douglas (MD) to address these deficiencies. The Board has also made a recommendation to improve the recognition of engine failures involving compressor stalls. Further, the Board has restated a previous concern about the lack of a requirement for operators to take into account the adverse effects of a wet runway surface on braking when calculating take-off performance.

The accident aircraft, a CAI DC-10-30ER, was on a scheduled flight from Vancouver to Taipei, Taiwan. During the take-off run, just after the aircraft accelerated through 167 knots, the crew heard a loud bang, felt considerable vibration and airframe shudder, and rejected the take-off. The aircraft could not be stopped on the runway, and the nose gear collapsed as the aircraft rolled through the soft ground off the end of runway 26. On board were 243 passengers and 14 crew. Six passengers were slightly injured during the emergency evacuation of the aircraft. The accident occurred at approximately 1330 Pacific daylight time (PDT).

The Board determined that the engine on the left wing lost power at a critical point in the take-off run and that the rejected take-off was initiated at a point and speed where there was insufficient runway remaining to stop the aircraft on the runway. Contributing to this occurrence were the misidentification of the cause of the loud bang and a lack of knowledge regarding the characteristics of engine compressor stalls. Contributing to the engine power loss was a delay between the collection and analysis of the engine monitoring data.

The compressor stall and loss of power, in the left engine, were the result of the failure of compressor blades in the high pressure compressor section of the left engine. Although the initiating mechanism of the blade failure could not be determined, the damage to the compressor had built up gradually.

The company's engine trend monitoring of its DC-10 engine indicated that there was a problem with the left engine for several days prior to the accident flight. But, the process used by the airline to analyse the engine trend data was not timely enough to result in the required maintenance action being taken before the flight.

Since this occurrence, CAI has enhanced its engine trend monitoring system to provide a near-real-time evaluation of the data to provide for more timely action on engine anomalies. Following the accident, the TSB forwarded a Safety Advisory to Transport Canada (TC) suggesting that other operators using engine trend monitoring systems be advised of the safety benefits of timely analysis of engine data. TC has taken this information and published it in a number of TC publications sent to the industry.

The captain did not recognize the loud bang as a symptom of a compressor stall on the high bypass ratio engine and thought that the noise might have been a bomb. Consequently, he decided to reject the take-off even though the speed was above V1 (the maximum take-off rejection speed). Although the flight crew members were all very experienced pilots and had taken simulator training throughout their careers, they had not been trained to recognize a loud bang as a symptom of a high bypass ratio engine compressor stall, and none of the crew members noticed the cockpit indications of power loss on the left engine.

Earlier studies on the recognition and correct identification of engine malfunctions by aircrews have shown that misdiagnosis of engine problems has been contributory to the outcome of many previous occurrences. Flight crews not recognizing the loud bang as a compressor stall have assumed the noise was caused by a bomb or something that might render the aircraft unairworthy and have unnecessarily rejected the take-off. Few resources are available to flight crews to aid them in the quick identification of engine failure conditions. Neither the engine manufacturers nor the aircraft manufacturers have specific information available on the characteristics of high bypass ratio engine compressor stalls. Currently there is no flight crew training available to provide positive recognition and correct identification of the engine failure symptom experienced on this accident flight. Because of the significant risks associated with unnecessary rejected take-offs, the Board has recommended that:

The Department of Transport ensure that flight crews operating high bypass ratio engines can correctly identify and respond to compressor stalls or surges. [A96 - 13]

Safety action has already been taken on a number of other deficiencies uncovered during the investigation: new procedures have been instituted for activating the antiskid braking systems during an emergency; new minimum equipment list procedures are in effect for disabled thrust reversers; new information has been added to the flight manual and crew training program concerning radio communication when on emergency power; stronger springs have been put on evacuation slide covers on DC-10 aircraft; the Take-off Performance Flight Planning software has been modified to provide crews with better information; and the Vancouver International Airport now has plans to commit its shuttle buses to assist the airlines in transporting passengers to the terminal from an occurrence site.

Rainy conditions and wet runways are fairly common at Vancouver International Airport. Calculations indicate that if the runway had been wet the aircraft would have required an additional 880 feet to stop and the consequences would have been much more serious. Yet, CAI, like other air carriers in North America, does not have any procedures to compensate for the reduced braking action that would occur as a result of a rejected take-off on a runway surface, nor is there a regulatory requirement to have such procedures.

Over the last 10 years, there have been various recommendations, studies and working groups pertaining to wet runway take-offs. Other than for newly certified aircraft, there is still no requirement for manufacturers to provide approved performance data for aircraft taking off on wet runways. Notwithstanding work in Canada and the U.S. to address this issue, the Board remains concerned that fare-paying passengers continue to be placed at risk when field-length-limited take-offs are conducted without taking into account reduced braking effectiveness on wet runways.

The Transportation Safety Board of Canada is an independent agency operating under its own Act of Parliament. Its sole aim is the advancement of transportation safety. It is not the function of the Board to assign fault or determine civil or criminal liability.

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