What happened
On 19 November 2013, a Boeing 737-33A, registration G-POWC, was operating a commercial cargo flight from Edinburgh Airport to Stansted Airport. The aircraft was carrying eight unit load devices (ULDs) intended for transport. During the takeoff roll, the pilot flying encountered unusually heavy back-pressure on the control column, which led to a sluggish and delayed rotation of the aircraft.
As the flight progressed through the climb, the crew noted that the aircraft required approximately 1 to 1.5 additional units of nose-up pitch trim compared to standard requirements. Although the crew suspected a loading error, they decided to proceed to the destination as the aircraft appeared to be flying normally. Upon arrival and subsequent inspection of the cargo hold, the crew discovered that the ULDs had been loaded in the exact opposite order of the intended plan.
The investigation
The investigation focused on the loading process and the resulting weight and balance of the aircraft. It was established that while the Load Order Form correctly specified that the heaviest containers should be placed toward the rear of the aircraft, the actual loading was performed in reverse. This placed the heaviest units in the forward section of the cabin.
Data from the flight data recorder (FDR) confirmed the abnormal handling characteristics. The aircraft began to rotate at approximately 141 KIAS, significantly later than the calculated rotation speed of 128 KIAS. Furthermore, the rotation rate was recorded at roughly 1 degree per second, which is much slower than the typical 2.5 to 3 degrees per second expected for this aircraft type.
Findings
- The primary cause of the incident was that the ULDs were loaded in reverse order to the intended plan.
- This error placed the aircraft's center of gravity at an index of 3.8 units, which was significantly forward of the flight envelope limit of approximately 16 units.
- The crew did not verify the final position of the containers after loading, partly because the operator's manual did not mandate a specific check of all positions, and because a rushed turnaround prevented the commander from performing a manual check.
- The heavy nose-down trim requirement was a direct result of the forward center of gravity.