History of the Flight
On 5 August 2016, at approximately 1135 UTC, a Robinson R44 Raven (registration G-RFUN) departed Coal Aston Airfield (elevation 720 ft amsl) with one pilot and three passengers. The pilot performed a vertical takeoff, climbing to about 50 ft before transitioning to forward flight. After about 15 minutes, the helicopter arrived at a boar shooting ground in the Peak District National Park at approximately 1,000 ft amsl. The pilot circled while losing height, then made a downwind approach on an easterly heading with full carburettor heat applied, establishing an out-of-ground-effect (OGE) hover at 70 ft agl with 23 inches of manifold pressure.
After 2 to 3 seconds in the hover, the pilot checked the instruments and then noticed the helicopter sinking. Raising the collective lever had little effect. Realizing he was too low to fly away, the pilot attempted to land on uneven ground to his right. He lowered the collective, yawed the helicopter into the hill, then raised the collective to cushion the touchdown. The helicopter landed heavily on the front of its skids and rolled onto its right-hand side, coming to rest. The pilot and passengers vacated through the left doors, with the front-seat passenger sustaining a small cut to his head; others were unhurt but shaken. The pilot secured the aircraft by turning off fuel and electrics. Ground marks indicated that the main rotor blades had struck the ground during the rollover.
Meteorological Conditions
Weather conditions were good with no significant cloud and good visibility. The Doncaster METAR at 1120 UTC reported wind from 280° at 10 kt, visibility more than 10 km, lowest cloud at 4,000 ft, temperature 21°C, and QNH 1020 hPa. The Manchester METAR at 1150 UTC reported wind from 270° at 11 kt, visibility more than 10 km, lowest cloud at 3,600 ft, temperature 19°C, and QNH 1018 hPa.
Weight and Balance
Initial loading calculations by the pilot suggested a combined pilot and passenger weight of 770 lb, placing the helicopter 29 lb above its maximum takeoff weight (MTOW) of 2,400 lb. These calculations did not include an aircraft cover and several litres of oil (approximately 17 lb) in a rear baggage compartment. A separate report indicated the pilot's weights were incorrect, with pilot and passenger weights of 182 lb and 609 lb respectively, giving a takeoff weight of 2,467 lb. The pilot later revised his weight to 154 lb and passenger combined weight to 574 lb. Direct contact with passengers yielded a combined weight of 595 lb, which would have placed the aircraft slightly above MTOW.
Aircraft Performance
The pilot performed a downwind transition to an OGE hover at the boar shooting ground (approx 1,000 ft amsl). The Robinson R44 Pilot's Operating Handbook (POH) performance section indicates that at this altitude and temperature, in zero wind, the helicopter should be able to hover OGE at MTOW (2,400 lb) with carburettor heat off. A note states: 'Full carburettor heat reduces hover ceilings by up to 2400 feet.' With full carburettor heat applied, the maximum weight for an OGE hover at that location would be approximately 2,230 lb.
Analysis
The pilot, with relatively low experience (87 hours total, 9 on type), flew the helicopter at close to maximum weight downwind to an OGE hover in hilly terrain with full carburettor heat applied. The POH performance figures show this was outside the declared flight envelope. Upon reaching the hover, the helicopter began to descend and probably entered a vortex ring state (settling with power) before landing heavily. The initial unsuccessful start-up attempt was considered unrelated.
Safety Messages
The CAA Safety Sense Leaflet No. 17 on helicopter airmanship contains advice relevant to preventing this type of accident.