What happened
On June 8, 2005, a Westwind 2 (registration N639AT) departed Shannon Airport, Ireland, operating as an air ambulance flight bound for St. Johns, Newfoundland, and Miami. The aircraft was carrying a crew of two and five passengers, including one patient.
While climbing through 16,000 feet, the crew heard a loud bang accompanied by a rise in the interstage turbine temperature of the left engine. A visual inspection revealed that a 6-foot section of the left wing de-icing boot had separated from the leading edge. As a precaution, the pilot retarded the left engine to flight idle and initiated an immediate return to Shannon. The aircraft landed safely at 13:24 hrs without any injuries to the crew or passengers.
The investigation
The investigation examined the aircraft's de-icing system and maintenance history. The aircraft utilized a pneumatic system where engine bleed air inflates rubberized boots to shed ice. Investigators found that a 6-foot 6-inch portion of the left wing boot had torn away and been ingested by the port engine, resulting in damage to 50% of the port engine fan blades.
Upon inspecting the wing, investigators discovered that the conductive edge sealer was in poor condition, with significant areas of the boot lifting or bubbling. Furthermore, pieces of silver adhesive tape were found on the wing leading edge where the boot had detached. This tape had been used to fill skin contours, rather than the aircraft structure filler recommended by the manufacturer.
Findings
- The primary cause of the incident was insufficient bonding between the de-icing boot and the wing leading edge, which allowed the material to detach.
- The de-icing boots had been poorly maintained, with evidence of improper repairs and the use of non-standard adhesive tape.
- The condition of the boots on both the port and starboard wings was found to be substandard, with visible wrinkling and lifting.
Safety action
A safety recommendation was originally directed toward the European Aviation Safety Agency (EASA) to review safety standards for Emergency Medical Service (EMS) operations to ensure higher maintenance and operational oversight within European airspace.