What happened
On 1 September 2003, an Advanced Technologies AT-10 Airship, registration G-OATG, was conducting a certification test flight near Cardington, Bedfordshire. The flight objectives included evaluating engine performance and control system dynamics following the installation of a new silencer. The flight crew performed timed acceleration runs at an altitude of 1,100 feet amsl over farmland, testing each engine individually while the other remained at idle.
During a repositioning manoeuvre, a fire was observed in the stubble of a field beneath the flight path. While the crew received no internal indications of any malfunction during the flight, a post-flight inspection revealed significant damage to the right engine silencer, including evidence of oil contamination. A local farmer later reported seeing debris falling from the airship during the testing period, which ignited the field.
The investigation
Investigators examined the silencer on the right engine, which consisted of concentric titanium tubes packed with stainless steel wadding. The inspection revealed that the perforated aft section of the inner tube and the internal stainless steel wadding were missing. Furthermore, a hole had been burnt through the bottom of the silencer, with molten titanium found on its rear face.
Further investigation into the right engine identified a leaking piston ring as the source of oil leakage. The investigation established that the stainless steel wadding ignited during the acceleration runs, leading to the structural failure of the silencer component.