Boeing 737-823 N831NN accident near Los Angeles, California

Probable cause

the early rotation of the airplane to an angle at which the fuselage contacted the runway.

Contributing to early rotation was the Captain’s reaction to the erroneous V1 automated callout, likely assuming that the airplane was at or close to the correct Vr at the same time.

The erroneous automated callout was likely due to a keystroke entry error by the FO when manually entering takeoff data for a newly assigned departure runway.

NTSB analysis

The crew reported that preflight preparation was normal, with the departure runway and takeoff data automatically uploaded to the airplane Flight Management Computer (FMC) via ACARS (Airborne Crew Addressing and Reporting System). Shortly before leaving the gate, Air Traffic Control (ATC) informed the crew that the departure runway was changed to runway 7L. According to American Airlines, on the B737-800, only the first four runways listed on the Takeoff Performance System (TPS) can be auto-loaded if a runway change occurs after the initial upload. Runway 7L was not one of the first four runways listed on the TPS, so the First Officer (FO) manually input the data, including the prescribed V-speeds using information on the preflight paperwork.

Flight planning data indicated that the conditions at the time of the accident called for a flaps 1 takeoff with V1 (takeoff decision speed) of 153 knots, a Vr (rotation speed) also of 153 knots, and V2 (scheduled takeoff speed) of 158 knots. The recorded data indicates the manually entered V speeds in the FMC were V1 of 123 knots, Vr of 153 knots and V2 of 158 knots. FMC data was not recovered, but the most likely reason for the inappropriate V1 value was determined to be a keystroke entry error by the FO when manually entering data.

During the takeoff roll, the Captain reported hearing the automatic, aircraft-generated V1 callout occur, and he began to rotate the airplane. Recorded data is consistent with rotation beginning as the airplane was passing through 123 knots, approximately 30 knots below the proper rotation speed. The airplane pitched up to about 11 degrees just prior to liftoff at 148 knots. The airplane operating manual specifies that tail contact will occur at 11 degrees of pitch if still on or near the ground. The manual also states that “Early, rapid or over-rotation may result in a tailstrike.” Although there was no mention of a "Vr" callout, V1 and Vr are typically close in value for a 737, so the Captain may have reacted to the erroneous V1 callout, expecting that the airplane was also at Vr. Had the Captain waited for a “Vr” callout by the FO, the erroneous V1 entry would have had no effect.

Post event examination revealed that the airplane experienced substantial damage to the lower rear fuselage.

Text from the NTSB. Open the NTSB docket for DCA11FA050 for the full record.