What happened
On 16 February 2002, a British Midland Embraer 145, registration G-RJXC, was operating a flight from Leeds to Paris when it encountered hydraulic difficulties. The aircraft was forced to divert to East Midlands Airport. During the approach, the deployment of full flaps caused the left outboard spoiler to open, creating a significant handling challenge. To maintain a level wing attitude, the pilot was forced to use more than 75% of the available control wheel and nearly full roll trim.
The investigation
Upon reviewing the flight data from the aircraft's Digital Flight Data Recorder (DFDR), investigators identified that data sampled at rates higher than one sample per second appeared to be failing to update correctly. This resulted in a series of identical, repeated values being recorded. Detailed inspection of the data revealed a "stepped" nature in the time histories, which was inconsistent with the actual dynamic movement of the aircraft during the landing flare.
Further analysis showed that the resolution of the recorded data was inadequately low and highly variable. For example, certain parameters remained constant for several seconds despite the aircraft undergoing physical changes. The investigation also noted that the recorded resolution for Normal Acceleration failed to meet international standards and the manufacturer's own design specifications. The AAIB noted that this issue was not present in all parameters, but specifically affected those sampled at greater than one sample per second, including pitch, roll, and various accelerations.
Findings
- The DFDR system on the Embraer 145 exhibited inadequate recording resolution and failed to update data at the required intervals.
- The anomalies were specifically observed in parameters sampled at rates exceeding one sample per second, such as pitch attitude, roll angle, and control positions.
- The investigation found that the errors were not isolated to G-RJXC, as similar faults were identified in four other incidents involving Embraer 145 aircraft operated by British Midland and British Regional.
- The AAIB concluded that the recording system was unreliable for accurately determining aircraft responses to control inputs and that the problem likely extended to all Embraer 145 aircraft.