The Royal Air Force Sport Parachute Association (RAFSPA) had wet-leased an Antonov AN 28 for a period of 10 days (27 August 1993 to 6 September 1993). The aircraft operated out of RAF Weston-on-the-Green, United Kingdom. On the second day of the lease, the aircraft was busy bringing parachutists to jump height for free fall parachuting over the airport.
The aircraft in its final position (© AAIB)
The aircraft had completed twelve flights of approximately 15 minutes each, carrying up to 17 parachutists per flight. For the thirteenth flight again 17 parachutists boarded the aircraft. After which the aircraft taxied towards runway 36, with the take-off clearance received the throttles were forwarded with the propellers in take-off pitch. The acceleration down the runway was normal and the aircraft lifted off without any issues.
The However, at ~500 feet AGL (Above Ground Level) both engines simultaneously suffered a total power loss. As they were at a low altitude the crew did not have much time to troubleshoot the problem or attempt an engine restart. The only option was a forced landing in a large field adjacent to the airfield. The landing was heavy, however, the passengers and crew were able to vacate the aircraft without injury.
The aircraft in better condition (© Sebök Balázs) The accident was investigated by the Air Accident Investigation Branch (AAIB). Several serious shortcomings in the operation of the aircraft were discovered during the investigation. They were listed in their final report as causal factors;
A latent defect in the electrical system caused a simultaneous total power loss as the flaps were retracted at 500 feet agl on the climb out, with automatic operation of both asymmetric spoiler systems.
The latent defect had been caused by the progressive loosening of a single earthing screw, which provided a common earth point for the flap electric signalling and propeller auto feathering systems. This induced a high resistance to earth at this point and caused feathering of both propellers when flap retraction was selected, in addition to automatic closure of both engine fuel shut-off valves (within the fuel control units) and extension of both outboard spoilers.
At manufacture in Poland, a single earthing point had been installed which was not in accordance with the design requirements for this aircraft type as issued by the Antonov Design Bureau, which had required dual combined earthing terminals for the flap signalling and propeller auto feathering systems.
The Antonov Design Bureau had never cleared this type of aircraft for flight with the aft clam-shell doors removed, or for parachute training.
This aircraft had been incorrectly granted an Aerial Work Permit for parachuting operations in the UK by the Department of Transport, assisted by the CAA, as a result of implicit reliance upon submitted documentation which was subsequently proven invalid.
The AAIB report, on which this blog is based, can be read by clicking on the .pdf file below;