Los Angeles, CA, USA
N831NN
BOEING 737-823
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.
HISTORY OF FLIGHT On January 3, 2011, at 1017 PST, a Boeing 737-800, N831NN, serial number 33211, operated by American Airlines as flight 1586, experienced a tailstrike upon takeoff from runway 7 left (7L) at Los Angeles International Airport (LAX), Los Angeles, California. No injuries occurred during the event. The flight landed uneventfully at Lester Pearson International Airport (YYZ), Toronto, Canada, where damage to the tail skid was discovered. Further damage to the aft pressure bulkhead was later discovered, and this damage was determined to be substantial under the provisions of 49 Code of Federal Regulations (CFR) 830.5. The airplane was registered to and operated by American Airlines, Inc. under the provisions of 14 CFR Part 121, as an international passenger flight. The flight was operated on an instrument flight rules flight plan. According to the captain, normal procedures were followed during preflight and taxi, including verification of the takeoff bug speeds. During the takeoff roll, the automatic, aircraft-generated V1 callout occurred and he began to rotate the airplane. The first officer did not call for rotation at that time. The captain applied nose up pitch command until he realized the indicated airspeed was too low. He said he then eased the nose of the airplane back down to the runway and re-rotated at the normal rotation speed, achieving approximately 10 degrees nose up at about 155 to 160 knots. The FO said he noticed that the automatic voice callout occurred about 20 knots early and observed the captain rotate for takeoff, but he said nothing to the captain for fear of causing confusion. The rest of the climbout, cruise, descent, and landing at Toronto was uneventful. According to the first officer, during preflight preparations, due to a last minute runway change, the takeoff data V speeds did not automatically upload into the flight management computer (FMC), so he manually entered the speeds using information on the preflight paperwork. Flight planning data indicated that the airplane takeoff weight was 161,037 pounds with a center of gravity at 22.5% mean aerodynamic chord, which under the conditions at the time of the accident should have resulted in 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 123 knots, Vr 153 knots and V2 158 knots. Recorded flight data indicate the control column began moving in the nose-up direction as the airplane was passing through about 123 knots indicated airspeed, and over about 5 seconds moved to about 7 degrees in the nose-up command direction. Flaps were set to 1 and leading edge slats were set to the mid-extend position. The column briefly moved toward about 5 degrees then returned to about 8 degrees in the nose-up command direction. The data indicated the airplane began pitching nose-up steadily, reaching about 10.5 to 11 degrees approximately 8 seconds after the beginning of the control column movement. Air/ground switches all transitioned to “air” about the same time as the airspeed passed through about 148 knots. Airplane pitch then continued to increase to about 15 degrees as altitude began to increase. During the flight, the flight attendants expressed concern that a tailstrike had occurred, and notified the pilots. The pilots then performed the quick reference handbook procedure for a tailstrike on takeoff. During a post-landing exterior inspection of the airplane, damage to the tailskid was discovered. The crew made an aircraft logbook entry, filed a damage-to-airplane report, and notified airline operations control. INJURIES TO PERSONS None DAMAGE TO AIRPLANE A pre-ferry bill-of-work inspection was accomplished in Toronto prior to departure, and the airplane was ferried to Tulsa, Oklahoma for inspection and repair. After the suspected tailstrike, the Boeing Aircraft Maintenance Manual (AMM) 05-51-32-2 inspection was performed on the airplane. This AMM inspection calls for inspection of the tail skid assembly, external skin of the upper and lower aft fuselage, internal fuselage structure aft of the wing, and a specific instruction to “Do a detailed visual inspection of the entire aft side of the [body station] 1016 aft pressure bulkhead. Give particular attention to the upper bulkhead structure between skin stringers S-10L and S-10R.” Damage to the airplane included abrasions to the tailskid assembly and ancillary components. Further repairs were required on external fasteners, skin and related components. The Aft Pressure Bulkhead (APB) was found to require repair due to “oil canning” (buckling) at the 12:30 location that involved placing a 0.040” repair doubler of about 18” by 24” along with 3 fillers around the damaged area. The Boeing structural repair manual states that the “oil can” condition will cause “the web to have a shorter fatigue life.” The reported damage affects the structural strength of the APB and therefore qualified as “substantial damage” per 49 CFR 830. Initial assessment by the operator could not with certainty conclude the APB damage to be from the tailstrike since they had seen similar damage on other airplanes. However a design change applicable to the accident airplane limits the observed damage to tailstrike loads. OTHER DAMAGE None PERSONNEL INFORMATION The pilot, age 55, held a valid FAA Class 1 Medical Certificate and Airline Transport Pilot Certificate with a B737 Type Rating. His last flight review was on June 4, 2010. He reported 1,189 hours pilot in command in the B737, with 165 hours in the preceding 90 days. The First Officer, age 59, held a valid FAA Class 1 Medical Certificate and Airline Transport Pilot Certificate with a B737 Type Rating. His last flight review was on June 15, 2010. He reported 105 hours of pilot in command time in the preceding 90 days. AIRCRAFT INFORMATION The American Airlines 737 Operating Manual states: “For optimal takeoff and initial climb performance, initiate a smooth continuous rotation at VR at a rate of no more than 2 to 3 degrees per second to an initial target pitch attitude of 10 degrees. Normal liftoff attitude is between 8 and 9 degrees providing 20 inches of tail clearance at flaps 1 and 5. Tail contact will occur at 11 degrees of pitch if still on or near the ground. After liftoff, continue to raise the nose smoothly at a rate of no more than 2 to 3 degrees per second toward 15 degrees of pitch attitude. CAUTION • Early, rapid or over-rotation may result in a tailstrike.” METEOROLOGICAL INFORMATION The LAX 1753 UTC (0953 PST) weather observation reported wind from 020 degrees at eight knots, visibility 10 miles, broken clouds at 2,000 feet and 5,500 feet, temperature 10 degrees C, dew point 7 degrees C, sea level pressure 30.08 inches of mercury. AIDS TO NAVIGATION N/A COMMUNICATIONS N/A AERODROME INFORMATION LAX runway 7L had a concrete, grooved surface, 12091 feet long by 150 feet wide, aligned to 069 degrees magnetic. The runway elevation was 118 feet above sea level with a 0.3% gradient. The runway was equipped with lighting and markings for precision instrument approaches, and no anomalies with the runway were noted. FLIGHT RECORDERS The cockpit voice recorder was overwritten during the flight to Toronto. The flight data recorder was downloaded by American Airlines with NTSB recorders lab concurrence, and raw data transmitted to the NTSB. American Airlines removed the flight management computer but was not able to download relevant non-volatile memory data. WRECKAGE AND IMPACT INFORMATION N/A MEDICAL AND PATHOLOGICAL INFORMATION N/A FIRE None SURVIVAL ASPECTS N/A TESTS AND RESEARCH According to American Airlines, on their B737-800 fleet the FMC is normally uploaded via ACARS (Airborne Crew Addressing and Reporting System). If a runway change occurs after upload, only the first four runways listed on the Takeoff Performance System (TPS) can be auto-loaded. In this event, the airport switched from a western flow to an east direction for takeoffs and landings. (runways 25 initially to runways 7) The runway assigned to this crew for takeoff was runway 7L. This runway was not one of the first four runways listed on the TPS, so this required the crew to manually input the data for runway 7L. Therefore, the recorded parameters from the FDR were manually entered into the FMC by the flight crew. ORGANIZATIONAL AND MANAGEMENT INFORMATION N/A ADDITIONAL INFORMATION None
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.
Source: NTSB Aviation Accident Database
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