What happened
During the final landing phase, the flightcrew detected a 30-knot loss of airspeed and received a cockpit warning. In response, the crew initiated windshear recovery procedures. Despite these efforts, the airplane continued its descent, and the tail of the aircraft collided with the runway.
At an altitude of 152.7 feet (radar altimeter), the aircraft was traveling at 150 knots. Flight data indicated that longitudinal acceleration decreased from 0.010 to -0.049 as the radar altimeter dropped to 134.3 feet, while engine N1 decreased from 62.1% to 43.8%. Within five seconds, the airspeed fell to 134.3 knots at an altitude of 41.7 feet, with the pitch attitude increasing to 3.2 degrees and N1 rising to 70.95%. Two seconds later, as the airspeed decreased further to 122 knots at an altitude of 8.6 feet, the pitch was at 7 degrees and N1 reached 89.8% when the collision occurred.
The investigation
The investigation examined the performance of the North sensor low level windshear alert system (LLWAS), which was functioning but failed to detect or advise of the windshear condition. It was determined that the location and height of the sensor did not conform to FAA guidelines. Environmental conditions at the time included a temperature/dew point spread of 81 degrees F and a density altitude of 8,900 feet, with reported winds from 270 degrees at 12 knots.
A critical communication gap was identified regarding a windshear pilot information report (PIREP). While approach control received the PIREP, Air Traffic Control (ATC) policy does not require such reports to be passed to the tower controller. Consequently, the flightcrew, who were monitoring the tower frequency as directed, did not receive the warning.