AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 ACCIDENT Aircraft Type and Registration: Airbus Helicopters AS355F1 Ecureuil II, G-OHCP No & Type of Engines: 2 Allison 250-C20F turboshaft engines Year of Manufacture: 1982 (Serial no: 5249) Date & Time (UTC): 29 March 2017 at 1155 hrs Location: Summit of Rhinog Fawr, Snowdonia Type of Flight: Private Persons on Board: Crew - 1 Passengers - 4 Injuries: Crew - 1 (Fatal) Passengers - 4 (Fatal) Nature of Damage: Aircraft destroyed Commander’s Licence: Private Pilot’s Licence Commander’s Age: 56 years Commander’s Flying Experience: 3,6501 hours (of which 102 were on type) Last 90 days - 9.0 hours Last 28 days - 1.5 hours Information Source: AAIB Field Investigation Synopsis The helicopter was flying on a Visual Flight Rules (VFR) flight plan from its operating base near Cranfield Airport on a direct track to a private site near Dublin. The weather on departure was suitable for VFR flight but, as forecast, deteriorated markedly in the area of Snowdonia with low cloud and rain. The helicopter flew over a witness 4.3 nm southeast of the accident site before disappearing into the cloud. Shortly afterwards it struck the east side of Rhinog Fawr Mountain, fatally injuring the five occupants. History of the flight The pilot and four family members had planned to fly from the helicopter’s operating base adjacent to Junction 13 of the M1 motorway, to a private site close to Dublin Airport before returning later that evening. The pilot had used two commercially available flight planning applications on his iPad, both for flight planning and during parts of the flight but it is not known what information he used. The maintenance organisation was contacted by the pilot on the evening before the flight and requested that the helicopter be ready for departure at 1000 hrs with full fuel. The Footnote 1 The pilot’s log book available to the investigation covered only the early part of his flying career and was incomplete. The total hours were identified from his aircrew medical renewal form and the total on type and last 90/28 days from the available technical log sheets. © Crown copyright 2018 62 All times are UTC AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 next morning, the engineer moved the helicopter from the hangar to a parking spot and then refuelled the helicopter to tanks full. One family member arrived shortly afterwards, followed by two other passengers, and all three occupied the rear seats. The engineer had moved off to refuel another helicopter and did not see which seat each passenger occupied. Another passenger arrived and sat in the front left seat and the pilot occupied the front right seat. The engineer did not see the pilot arrive but noticed that the passengers had no luggage other than carrier bags. The helicopter was heard to start up and departed at about 1045 hrs. The GPS derived ground track and vertical profile of the flight are shown in Figure 1 and Figure 2. Dublin Airport x x Weston Airport RAF Valley x start of descent wreckage site RAF Shawbury x 1:57:14 - 1:55:32) - Birmingham Airport x 1:32:54) - (1 last recorded position 1 (last radar contact 1 1:13:06) - (1 - airborne 10:45:15 x Luton Airport Figure 1 Planned route (blue) and actual track (red) Figure 2 GPS derived vertical profile of the accident flight © Crown copyright 2018 63 All times are UTC AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 The helicopter was flown along the direct track from the departure point towards the destination achieving a maximum altitude of 3,000 ft at about 1142 hrs. The heights flown appeared to approximate to remaining below the main cloud base in order to maintain Visual Meteorological Conditions (VMC). A full description of the weather is included in the Meteorology section of the report, but in order to consider the weather encountered during the transit, the METAR cloud base for the airfields shown at the nearest time were: ● Luton Airport at 1050 hrs, cloud overcast at 1,200 ft, ● Birmingham Airport at 1120 hrs, cloud broken at 1,500 ft, ● Shawbury at 1120 hrs, cloud scattered at 1,400, broken at 3,000 ft, ● Valley at 1150 hrs, cloud broken at 600 ft. At what he estimated was between 1130 and 1150 hrs, a witness was located in Coed Brenin Forest, 4.3 nm southeast of the accident site. He saw a helicopter pass overhead and watched it for some 5 - 10 seconds before it went into the cloud cover. He reported the elevation of his position as 120 m (400 ft) at which time the helicopter was at 2,500 ft. A replay of the NATS radar tape for the appropriate time, showed only G-OHCP in the area and flying on its track with no other aircraft in the vicinity. The helicopter had been in a gentle descent from its maximum height to 2,500 ft before descending to 2,060 ft when it struck the east side of Rhinog Fawr Mountain, at about 1157 hrs. At the moment of impact, the auto pilot was engaged with the heading (HDG), turn coordinator (T/C) and vertical speed (V/S) modes active. This was consistent with a pilot-managed, autopilot-flown descent. Accident site The accident site was located on the south-east face of Rhinog Fawr in southern Snowdonia, at an elevation of 2,060 ft amsl, approximately 300 ft below the summit shown in Figure 3. The helicopter had struck a rock outcrop (Figure 4), completely destroying the cabin section and depositing wreckage along a trail 150 m in length, oriented on a heading of 280°M. The helicopter’s main rotor, gearbox and engines had separated from the fuselage and continued over the rock outcrop, coming to rest 140 m from the initial impact. The degree of disintegration of the cabin indicated that the helicopter had been flying at cruising speed immediately prior to impact. Witness marks made by the cabin, right skid and right horizontal stabiliser on the rock outcrop showed that the helicopter was in an approximately level pitch and roll attitude at impact. All major parts of the helicopter were identified at the accident site. A number of wreckage parts were burned and a small part of the impact area also exhibited evidence of burning, indicating that an intense, short-duration fuel fire had occurred after impact. There was a strong smell of unburned aviation fuel at the base of the rock outcrop, immediately below the impact area. © Crown copyright 2018 64 All times are UTC AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 One of the main rotor blades was heavily impact-damaged, indicating that the main rotor had been rotating at impact. Both tail rotor blades were damaged, consistent with rotation under power at impact and rotational scoring marks on the tail rotor drive shaft were further evidence of tail rotor rotation at impact. Figure 3 Location of the accident site Figure 4 Section of the accident site wreckage trial © Crown copyright 2018 65 All times are UTC AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 Aircraft description G-OHCP was an AS355F1, a twin-engine light helicopter configured to carry a pilot and five passengers. The AS355F1 is powered by two Rolls-Royce (Allison) model 250-C20F gas turbine engines which drive a three-bladed main rotor system through the main gearbox (MGB). Each engine drive input in the MGB is fitted with a freewheel unit that is designed to allow normal operation in the event of an engine failure. The AS355F1 is equipped with two independent hydraulic systems and is controlled by hydraulically-assisted flying controls. The pilot’s control inputs are transmitted through a series of control rods, bell cranks and mixing units to three hydraulic actuators attached to the MGB and a single tail rotor actuator which change the pitch of the main and tail rotor blades respectively. The hydraulic system is powered by two pumps mounted on the MGB. In the event of a hydraulic system failure, the helicopter can continue to fly in response to the pilot’s control inputs. G-OHCP was fitted with analogue flight instruments and a panel-mounted Garmin GNS430 GPS display unit. In addition, the helicopter was fitted with an SFIM 85T31 three axis autopilot, capable of controlling the helicopter’s desired flight path by inputs from electro-mechanical actuators mounted in series to each of the pitch, roll and yaw flight control linkages. The autopilot was controlled by an autopilot mode control panel, mounted on the centre instrument console. Detailed examination Flight instrumentation All the helicopter’s flight instruments had been severely damaged during the impact sequence. The pilot’s artificial horizon and the standby artificial horizon were disassembled and examined in detail. Both units had suffered from significant internal damage. Circumferential scoring was identified on the gyroscope of the pilot’s artificial horizon and rotational damage was observed on the cooling fins of the standby artificial horizon gyroscope wheel (Figure 5), indicating they were both operational at the time of impact. Circumferential scoring Figure 5 Pilot’s artificial horizon gyroscope exhibiting circumferential scoring © Crown copyright 2018 66 All times are UTC AAIB Bulletin: 3/2018 G-OHCP EW/C2017/03/02 GPS system The Garmin GNS430 fitted to the helicopter was recovered and examined in detail. No information about the accident flight or any preceding flights were recovered from the unit. A modification is available for the GNS430 that introduces a terrain warning function.