Cites Possible Maintenance Error In Connecting Antiskid Sensors

In its continuing investigation of an incident in which a United Airlines Airbus A320 departed the runway during landing at Wyoming's Jackson Hole Airport on the evening of February 25, the National Transportation Safety Board (NTSB) has developed the following factual information during its on-scene investigation.

Investigators with the safety board have determined the airplane came to rest 116 feet past the end of the runway, and 140 feet to the right of the runway centerline. A heavy skid mark was found on the runway associated with the inboard tire of the left main landing gear. This tire was found deflated and showed wear consistent with a skid. Upon exiting the runway, both engines ingested snow and sustained internal damage. The aircraft itself was not substantially damaged.

Examination of the left main landing gear brakes revealed that the inboard and outboard wheel speed tachometer wires were cross-connected. Such a configuration would be likely to cause the antiskid system to use the inboard wheel speed to control the outboard braking, and vice versa. In such a situation, it would be likely that when the inboard tire began to skid, the antiskid system would release the pressure on the outboard brake instead of the inboard brake.
 
Examination of maintenance records indicated that both main landing gear units were replaced on the incident airplane in early February 2008. The Safety Board is also investigating another United A320 incident with similar circumstances that occurred on October 9, 2007.

Another area of the investigation is the inoperability of one of the emergency evacuation slides. The slide at the front left door deployed when the door was opened during the evacuation but did not inflate. The manufacturer of the slide will assist the NTSB in its investigation of the cause of the failure.

Information obtained from the flight data recorder (FDR) and the cockpit voice recorder (CVR) is being analyzed at the Safety Board's laboratory in Washington.

Investigators are continuing to gather factual information in aircraft performance, human factors and other areas.

FMI: www.ntsb.gov