What happened
On 5 April 2006, a Pegasus Quantum 15-912, registration G-BYNO, was performing an air experience flight at Clench Common Airfield in Wiltshire. The flight, which was an instructional lesson for a passenger, proceeded normally until the aircraft was approximately 80 feet above the ground on final approach. During this phase, the aircraft encountered turbulence caused by nearby woodland.
Witnesses and the passenger reported hearing a loud noise, followed by the wing pitching up and the aircraft turning sharply to the right. A trailing wire was observed striking the propeller. The aircraft subsequently struck and penetrated the roof of a barn located near the landing threshold. The impact resulted in two serious injuries to the crew and passenger, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and found that all four rigging cable assemblies had failed. While the cables were made of the correct wire rope and were of the correct length, the metal ferrules used to secure the loops were not manufacturer-approved. These locally made assemblies had been installed approximately two weeks prior to the accident.
Laboratory analysis revealed that the ferrules used on G-BYNO had a thinner wall than factory-supplied parts. Furthermore, the copper used in these ferrules was significantly harder than the copper used in approved components. This increased hardness likely reduced the friction between the ferrule and the wire rope. Destructive testing confirmed that the cables failed because the wire rope pulled through the ferrules, rather than the wire itself snapping.
Findings
- The primary cause of the accident was the use of non-approved, locally manufactured cable assemblies featuring incorrect ferrules.
- The thinner wall thickness and increased hardness of the replacement ferrules resulted in insufficient grip on the wire rope.
- The failure of the forward cables caused the wing to pitch up and the aircraft to turn right.
- The decision to use unapproved parts instead of factory-supplied components was a critical link in the accident chain.