What happened
Prior to landing, the flight crew received and acknowledged reports that the braking action on the runway was rated as 'fair.' Following touchdown, the first officer engaged reverse thrust to decelerate the MD-80. The crew subsequently observed that the aircraft was not slowing at the expected rate. In response, the captain took control of the aircraft and applied maximum braking and reverse thrust; however, the airplane failed to stop and continued off the departure end of the runway.
The investigation
Post-incident measurements of the runway indicated that braking action was reported as 38 (fair), 23 (poor), and 27 (poor). An examination of the flight data recorder showed that the spoilers remained in a retracted position from the moment of touchdown through the entire rollout until the aircraft reached zero airspeed.
According to the MD-80 Flight Crew Operating Manual, the automatic brake system (ABS) landing mode is activated only when spoilers are deployed either manually or automatically. Furthermore, the Pilots Reference Manual's section on Abnormal Flight Profiles notes that ground spoilers significantly increase the effectiveness of braking and that ensuring their extension is necessary for a maximum performance stop. A review of the airline's Normal Checklist indicated that it was the responsibility of the pilot not flying to ensure that the spoilers were in the 'ARM' position.