What happened
On 4 August 2001, an Aerostar SA Yak-52, registration G-YAKY, was participating in a private formation flight near the Lake District. The flight had begun earlier that day at Bagby, North Yorkshire, where the aircraft had been refuelled. During the initial departure, the crew identified fuel escaping from the left wing due to an incorrectly fitted fuel cap. After a brief landing and re-securing of the cap, the aircraft rejoined its formation partner to continue toward Carlisle Airport.
While flying approximately five miles south of Carlisle, the aircraft experienced a significant loss of engine power. The engine remained operational but was restricted to idle power. The pilot attempted several recovery procedures, including the use of carburettor heat, manual fuel priming, and adjusting the propeller pitch. To allow the pilot to focus on these engine restart attempts, the passenger, an experienced pilot, took control of the aircraft to select a landing site and manage the approach.
Upon resuming control, the pilot noted a high rate of descent and a steep approach angle. In a late attempt to mitigate the impact, the pilot deployed the landing gear. The aircraft struck the ground in a right-wing-low attitude with the gear only partially extended. The impact caused the landing gear to collapse, and the aircraft slewed 90 degrees before coming to a halt. Both the pilot and the passenger sustained minor injuries.
The investigation
The investigation examined the engine, which had been recently installed following an overhaul and had only four hours of operation since installation. While the engine damage prevented a full test run, no external mechanical failures were immediately apparent. An inspection of the fuel system by an insurance loss-adjuster confirmed that fuel was present in the system up to the carburettor and that both tanks contained significant fuel levels.
Investigators also considered the possibility of induction icing, as weather charts indicated a moderate risk under the prevailing conditions. Furthermore, the investigation looked into the aircraft's landing gear deployment. Although the Pilot's Operating Handbook recommends keeping the wheels up during a forced landing to minimize airframe damage, the pilot had deployed them to absorb energy during the hard touchdown.
Findings
- The aircraft suffered a loss of engine power while in cruise flight.
- The pilot attempted various restart techniques, including pumping the throttle, which provided only momentary power.
- The decision to deploy the landing gear during the final approach contributed to the extent of the airframe damage.
- The aircraft's high rate of descent in a gliding configuration made the approach difficult to manage.
- There was no definitive evidence to confirm or rule out fuel system imbalances or induction icing as the primary cause.