Synopsis
On 24 October 2011, a Boeing 737-8AS, registration EI-DPA, suffered rudder system damage after being struck by a rare microburst while parked overnight at Faro Airport (LPFR), Portugal. The damage, which was not detected during subsequent checks, led to significant control difficulties on the aircraft's next departure. The flight crew managed the situation and returned to Faro for a safe landing.
History of the Flight
During the early hours of 24 October 2011, a violent storm associated with a supercell produced a microburst at Faro Airport, with recorded wind speeds up to 84.9 knots. EI-DPA, parked on the ramp, jumped its chocks and pivoted nose left, with the nose landing gear moving approximately 5 metres from its original position. The aircraft was released to service at 05:00 hrs following a Ramp-1 Check, but the Technical Log contained no reference to the overnight winds or the aircraft's movement. Other aircraft owned by the operator also moved but no damage was subsequently reported.
The first flight of the day for EI-DPA was a scheduled service to Beauvais, France. The Commander, aware of the overnight storm, conducted an extra-vigilant pre-departure walk-around. He found sand and grit in the engines and fibreglass insulation material behind the No. 1 engine fan. An engineer removed the material and confirmed the aircraft had been checked. The flight crew performed standard pre-departure flight control checks with no anomalies, and the taxi to the runway was normal.
Flight Crew Actions
The aircraft was cleared for take-off on Runway 28 at 17:06 hrs, with a wind check of 310°/15 knots. The initial take-off roll was normal, but upon rotation, the aircraft drifted right and required almost full left aileron deflection to maintain control. The First Officer (PF) noted the aircraft did not feel right. Engine indications were normal, ruling out an engine failure. During the climb, the aircraft exhibited a right roll tendency. The First Officer applied left rudder trim; however, it was initially insufficient to engage the autopilot. After retracting flaps and completing a 90° right turn, more left rudder trim was added, engaging the autopilot with approximately eight units of left rudder trim required to centralise the control column.
The flight crew level off at FL120 near Faro, per ATC clearance, rather than the cleared FL240. The Commander consulted the Quick Reference Handbook for jammed or restricted controls but determined the controls were not jammed but merely out of trim, so no applicable checklist existed. Using the operator's problem-solving model, they decided to return to Faro. The Commander briefed the cabin crew and passengers, and a normal flap 30 landing was planned for Runway 28. The First Officer conducted the approach and landing, which was described as normal, touching down at 17:36 hrs. After taxiing to the terminal, engineering staff boarded and determined further checks were needed; passengers disembarked.
Damage
Following the aircraft's return, the Commander noted in the Technical Log that a large left aileron deflection was required on rotation and approximately eight units of left rudder trim were needed. Engineering staff removed panels from the vertical stabiliser and found damage to the support brackets of both the Main and Standby rudder Power Control Units (PCUs), including cracking, fracturing, and displacement. The damage was not visible from the ground and had not been detected during the Ramp-1 Check or pre-flight checks.