Northwest Airlines Flight 985

The Airbus A320 contacted the runway and the terrain during takeoff on runway 3C (8,500 feet by 200 feet, wet) at the Detroit Metropolitan Wayne County Airport. An emergency evacuation was made during which time the emergency evacuation slide on the 2 left (2L) door failed to deploy. The captain reported that during the initial takeoff run, he held half forward pressure until reaching 80 knots. He reported that up to this point, everything was normal. He stated he released forward stick pressure by about 100 knots and the nose of the airplane began lifting off the ground with neutral stick, which was not normal. He reported he applied about half forward stick and the nose came back down. He reported that at 120 knots the nose again began to rise with one half to one quarter stick input. He then pushed the stick forward to the forward stop and the nose came up at a rapid rate. The captain reported that his attention was focused outside the airplane and he did not hear the first officer call V1. He reported that he felt the airplane was going to stall so he pulled the power off and aborted the takeoff. The captain stated that he was trained not to perform high-speed aborted takeoffs, but he felt the airplane would have been uncontrollable if the takeoff continued. The captain stated the thrust reversers were deployed and he initially thought there was enough runway remaining to stop. He assumed the autobrakes activated, but he pressed on the brakes anyway. He reported the airplane was not decelerating and it departed the end of the runway at a high speed. The captain reported that deceleration was rapid once the airplane departed the paved surface and the engines flamed out during the ground roll. Post accident inspection of the airplane revealed the horizontal stabilizer trim was set to negative 1.7 (units of trim), when it should have been set at positive 1.7. The first officer stated he set the trim while on the taxiway. The captain did not notice the improper trim setting during the cross check which was part of the taxi checklist. Further investigation revealed the operator procedures were to set the trim using units instead of percentage of mean aerodynamic chord as recommended by the manufacturer. In addition, it was discovered that the manner in which the units of trim were displayed on the trim control wheel, on the electronic centralized aircraft monitoring system (ECAM), and in the aircraft communications addressing and reporting system (ACARS) were not consistent. As a result the Safety Board issued Safety Recommendations A-02-06 and A-02-07. Post accident examination of the 2L slide/raft that did not deploy revealed an improper chamfer on the telescopic girt bar which attaches the slide/raft to the airplane structure. This allowed the slide/raft to detach from the airplane when the 2L door was opened. As a result the Safety Board issued Safety Recommendations A-01-27 and A-01-28. Being a fly-by wire airplane, the Airbus A320 has two sources of control lag in the pitch control. One is the latency between the pilot's input and the elevator movement through the elevator aileron control (ELAC) computer and the other is the rate limit of the elevator. Examination of the digital flight data recorded data for this accident revealed the pilot changed the pitch input faster than the elevator system would respond and saturation occurred in the rate at which the elevator surface could respond to the inputs. This resulted in pilot inducted oscillations (PIO) during the takeoff roll.

Verbatim NTSB analysis and probable cause from the NTSB dataset