What happened
On 8 April 1998, two aircraft were engaged in a training session for a seven-aircraft formation aerobatic display over Boreham Airfield, Essex. The formation consisted of a lead Yak 52, registered LY-AMUS, and a No 6 aircraft, a Yak 50, registered G-BWYK. The flight was conducting formation aerobatic training at approximately 1,500 feet.
The maneuver being practiced was a "1/2 Cuban" in a line astern configuration. During the sequence, the No 2 and No 3 aircraft departed the formation just before the vertical climb, leaving the leader and the No 6 aircraft in a line astern position. As the leader prepared to initiate the roll-out by making a 'check' call, the aircraft experienced three distinct impacts at the rear.
Following the impact, the pilot of LY-AMU struggled to roll the aircraft upright and informed the No 6 pilot that a collision had taken place. The pilot of G-BWYK noted a brief propeller impact but reported no significant vibration. Upon inspection, it was discovered that approximately 30% of the right elevator structure and skin on the Yak 52 had been destroyed. The Yak 50 returned to North Weald Airfield and landed safely, while the leader performed a handling check and landed the Yak 52 following a flapless approach.
The investigation
The investigation was based on the aircraft accident report submitted by the pilot. Investigators examined the sequence of the maneuver and the pre-flight procedures. It was established that while the maneuver had been performed safely in previous sessions, the specific positioning of the aircraft during this flight led to the contact.
Findings
- The collision occurred because the Yak 50 was positioned too closely to the leader during the roll-out phase of the maneuver.
- The formation leader did not sufficiently emphasize the necessity for the No 6 aircraft to increase separation from the leader before the application of forward elevator during the roll erect.