What happened
On February 24, 2001, a Boeing 737-300 operating a cargo flight from Frankfurt/Main to Bergamo experienced significant flight control difficulties. During takeoff, the flight crew noted that the aircraft failed to rotate at the calculated rotation speed (VR) of 133 kt. Although the pilot considered aborting the takeoff, the decision was made to continue as the aircraft had already exceeded the decision speed (V1) of 132 kt. The aircraft eventually lifted off at approximately 155 kt, nearly 20 kt above the intended VR.
During the climb, the crew observed an unusual stabilizer trim setting of approximately 7, which was significantly higher than the normal range. The flight continued to Bergamo, where the crew encountered similar issues during a circling approach. The aircraft exhibited sluggish handling, and the crew struggled to maintain the 3-degree glide path. Upon landing, the aircraft was difficult to rotate and experienced a significant vertical acceleration of 1.76g.
The investigation
The BFU investigation, conducted alongside the airline's flight operations inspectorate, revealed that the aircraft was loaded with three full containers instead of the three empty containers originally planned. This error resulted in the aircraft being 6,116 kg heavier than stated on the Load & Trim Sheet. Consequently, the center of gravity (CG) remained outside the permissible operational limits throughout the entire flight.
The investigation found that the takeoff and landing speeds used by the crew were incorrect for the actual mass of the aircraft. While the crew calculated speeds based on a takeoff weight of 45.9 tonnes, the actual takeoff weight was approximately 51 tonnes. Furthermore, the investigation utilized a flight simulator at a flight school in Bremen to replicate the flight parameters, confirming the crew's observations of extreme longitudinal instability.
Findings
- The primary cause of the flight disturbance was that the aircraft was operated with a center of gravity outside the allowable range.
- A loading error occurred in Frankfurt because the ramp agent failed to verify that the containers delivered for sectors A, B, and C matched the load sheet requirements.
- The aircraft was significantly heavier than documented, leading to incorrect V-speeds (V1, VR, and V2) and an insufficient landing reference speed (VREF).
- The combination of an extreme forward CG and insufficient airspeed severely compromised the longitudinal controllability of the aircraft during takeoff and landing.
- The airline's operations manual lacked procedures for identifying or managing flights with an out-of-limits center of gravity, and such scenarios were not included in simulator training.
Safety action
Following the investigation, the BFU issued two safety recommendations:
- The airline should update its Operations Manual for the Boeing 737 to include procedures for identifying flights with a center of gravity outside the permitted limits.
- Flights involving an out-of-limits center of gravity should be incorporated into simulator training as a potential flight scenario.