What happened
On 1 December 2023, a Boeing 737-4K5, registration G-JMCV, was preparing for a cargo flight from East Midlands Airport to Aberdeen Airport. During the pre-flight phase, the crew received a packet of documents that included a load sheet from a previous flight. Unaware of the error, the crew used the figures from this incorrect document to calculate takeoff performance using the Onboard Performance Tool (OPT).
As a result of using the wrong data, the aircraft was approximately 10 tonnes heavier than the crew had calculated. During the takeoff roll, the commander initiated rotation at 123 knots, which was 15 knots slower than the 139 knots required for the actual mass. While the rotation felt normal, both crew members noted a small bump. Because there were no immediate abnormal flight indications and the commander was managing a high workload due to an inexperienced co-pilot, the decision was made to continue the climb to cruising altitude.
During the cruise at FL240, the crew evaluated the possibility of a load shift. After the co-pilot confirmed the cargo appeared secure, the commander decided to perform the tail strike checklist out of caution. Following a descent to FL90, the crew proceeded to Aberdeen. Upon arrival, a walk-around inspection revealed damage to the drainage mast and the tail skid.
The investigation
Investigators examined the aircraft's Quick Access Recorder (QAR) data, which confirmed that the rotation speed was significantly lower than required for the actual weight. The data showed the aircraft's pitch rate peaked at 5°/s just before liftoff, and the pitch attitude reached 12.3°, exceeding the 11.4° threshold for a tail strike.
Analysis of the performance calculations revealed that the incorrect load sheet led to a lower calculated thrust setting and a more nose-up stabilizer trim setting than necessary. This combination caused the aircraft to rotate at an insufficient speed to generate the lift required for its actual mass, leading to the tail striking the ground as the aircraft struggled to lift off.
Findings
- The crew utilized incorrect loading figures from a previous flight to determine takeoff performance.
- The aircraft departed approximately 10 tonnes heavier than the crew had anticipated.
- The takeoff rotation was initiated 15 knots below the required speed for the actual aircraft mass.
- The use of erroneous data resulted in a mis-trimmed stabilizer and an inappropriate rotation speed, causing the tail to strike the ground.