What happened
On 2/5/11, a Chinook HC Mk 3, registration ZH898, was operating as part of a two-aircraft formation (callsign Pegasus 2) for an Operational Conversion Flight training syllabus. The sortie, conducted by 18 (B) Sqn from RAF Odiham, involved staged descents to altitudes as low as 50ft AGL to train student crews in tactical formation and low-level flying.
During the return leg of the flight, while transiting south-westerly near Uffington, ZH898 was operating at a radar altitude between 80ft and 100ft AGL. The aircraft flew directly over two horse riders traveling along a minor road. Due to high hedgerows obscuring the view of the road from the air, the crew was unaware of the riders' presence. One rider fell from her horse during the overflight, sustaining serious injuries.
The incident was observed by a student pilot positioned in the rear cabin of the aircraft. Upon realizing the accident had occurred, the captain directed the formation to climb and subsequently returned to the site at 1000ft to confirm the situation. The crew requested emergency services via Benson Approach and then returned to RAF Odiham.
The investigation
The investigation examined the flight planning, aircraft serviceability, and crew backgrounds. It was established that ZH898 had undergone a before-flight service earlier that day and that both aircraft in the formation had functional RADALTs. The training sortie had been authorized with specific parameters allowing for flight down to 50ft AGL.
The investigation also reviewed the circumstances of the riders, noting they were traveling on a road where the view of the path was partially obstructed by tall hedges. Following the incident, the aircraft's Data Acquisition Processing Unit (DAPU) and Health and Usage Monitoring System (HUMS) cards were removed for data extraction.