What happened
On 15 January 2017, a Bombardier BD100 1A10, registration 9H-VCJ, was conducting a positioning flight from Riga, Latvia, to Dublin Airport. While descending through approximately 4,200 feet, the crew used the flight spoilers to reduce speed as requested by Air Traffic Control. Upon retracting the spoilers, the crew received a caution message on the EICAS indicating a spoiler fault, specifically involving the right outboard Multi-Function Spoiler (MFS).
Following the established checklist, the crew increased their approach speed to Vref +8 knots. However, as the aircraft descended and the pilot selected landing flaps (30°), the aircraft became difficult to control in roll. The pilot experienced a sensation of "two stops" on the control wheel and a time-lag in aircraft response, leading to a pilot-induced oscillation. To regain control, the pilot increased the approach speed to approximately 160 knots. The aircraft subsequently landed at Dublin Airport without further incident, and there were no injuries.
The investigation
The AAIU examined flight data from the FDR, which revealed that after the flight spoilers were retracted, the right outboard MFS re-extended to approximately 7° and remained at that position for the rest of the flight. The investigation also reviewed the aircraft's certification standards, noting that while the manufacturer had tested for a fully jammed spoiler (45°), the specific scenario of a spoiler stuck at an intermediate angle (7°) had not been the primary focus of the certification-critical case.
Findings
- The uncommanded extension of the right outboard MFS was likely caused by a wiring or connector continuity issue at the spoiler's PCU connection.
- The aircraft experienced alternating airflow separation and reattachment on the flap behind the partially extended spoiler, which created the roll control difficulties.
- The existing Quick Reference Handbook (QRH) guidance for a spoiler fault did not account for a spoiler remaining stuck at an intermediate position, which contributed to the difficulty in managing the approach at the prescribed lower speed.