What happened
On 9 February 2011, a PA 31-350 cargo aircraft, registration G-VIPY, was conducting a scheduled flight from East Midlands Airport, UK, to Weston Aerodrome, Co. Dublin. During the descent phase, the pilot activated the de-icing system, noting a slight shudder but no immediate issues. Shortly thereafter, the aircraft was struck by a violent rolling motion.
Upon inspection, the pilot discovered that the inboard section of the starboard de-icing boot had partially detached and was flailing in the airflow. This movement caused the material to strike the starboard wing, aileron, and flap, making the aircraft extremely difficult to control. The pilot declared a PAN to Dublin Air Traffic Control. While Dublin ATC suggested an emergency landing at Dublin Airport, the pilot eventually observed that the detached section of the boot had completely separated from the aircraft and fallen into the sea. Once the flailing material was gone, normal handling returned, and the pilot elected to continue the approach to the original destination, landing safely at Weston.
The investigation
AAIU inspectors examined the aircraft at Weston Aerodrome and reviewed maintenance logs. The investigation confirmed that a 1.55-meter section of the starboard de-ing boot had peeled away from the leading edge. This separation caused visible damage and marking to the upper surface of the starboard wing, the starboard aileron, and the outboard portion of the starboard flap. The peeling process appeared to have been stopped only by the stall warning vane and its bracket.
Maintenance records indicated that the aircraft was well-maintained. The de-icing boot and its adhesive were from approved sources and were within their service life. No defects regarding the boot had been noted during previous scheduled inspections. Because the detached portion of the boot was lost in the Irish Sea, a detailed examination of the failed component was not possible.
Findings
- The aircraft's severe rolling motion was caused by the partial separation of the starboard de-icing boot.
- The flailing material caused physical damage to the starboard wing, aileron, and flap.
- Flight control difficulties ceased once the detached section of the boot fully separated from the airframe.
- An unexplained landing gear warning light illuminated at the same time the control issues ended, though cycling the gear resolved the light.
- There was no evidence of improper maintenance or expired components contributing to the failure.