AAIB Bulletin: 10/2018 G-CTFL and G-HYND EW/G2018/05/07

towards him. He attempted to turn his radio on and replace his headset, so that he could warn the other pilot but, before achieving this, he observed one of his rotor blades strike the left side of G-CTFL’s engine bay. The impact did not seem to affect his own helicopter and his passengers appeared uninjured so, when the rotor blades stopped rotating, they all disembarked normally. CCTV recordings of the collision showed that G-CTFL pitched rapidly to approximately 45º nose-down but initially maintained its height above the ground, while moving away from 64 ©Crown copyright 2018 All times are UTC AAIB Bulletin: 10/2018 G-CTFL and G-HYND EW/G2018/05/07 G-HYND, and towards the helipad. As it approached the pad it descended and the nose pitched up, the tail struck the grass and the rear of both skids hit the concrete. This caused G-CTFL to bounce approximately two feet from the ground, into a nose-down attitude, while the tail turned anti-clockwise towards the R22. Next, G-CTFL impacted the ground heavily, orientated at 90º to the pad, with the left skid hitting first and the helicopter then rolling onto its right skid and pitching nose-up until the tail struck the ground near the R22. G-CTFL now bounced a second time, its tail turned quickly clockwise and the helicopter rolled left until the main rotor blades struck the concrete pad. Finally, G-CTFL struck the ground between the two landing pads with its tail on the grass and close to the R22. The rotor blades stopped turning 33 seconds later. During the accident sequence, the CCTV recording showed debris being thrown several metres across the surrounding area, with some falling onto Apron A. Approximately three minutes after the accident, the pilot of the Cessna aircraft taxied via Taxiway A to another position at the airport, for refuelling, after advising the Air/Ground operator of his intention. The Cessna’s pilot later recalled that he was aware the helicopter’s “undercarriage” had collapsed but he did not observe the accident or see any debris, so had not considered the potential for his aircraft to have been damaged. With hindsight, he realised that he could have shut down and inspected his aircraft but, as he was not departing for a flight, he thought that with the situation under control, it would be best if he moved away. He assumed the taxiway was safe to use, as he had watched a Rescue and Fire Fighting Services (RFFS) vehicle being driven along it before he taxied. RFFS response The operator of Cumbernauld Airport had agreed that the helicopter operator would provide RFFS in respect of all associated helicopter operations and consequently the helicopter operator’s own RFFS vehicle was available. This was situated outside the hangar, a few metres from the accident site, but the only trained RFFS personnel available were the pilots from the R22 and from G-HYND. Another employee was the first to reach the accident site and he saw no evidence of leaking fuel when he assisted the passengers to escape. Subsequently the R22 pilot reached the scene and determined there was no fire risk, so the operator’s RFFS vehicle was not employed. The airport’s Air/Ground radio operator activated the airport crash alarm. He was also trained for RFFS duties and, when he did not see the helicopter operator’s RFFS vehicle deploy, he passed his radio task to somebody else, and drove the airport’s RFFS vehicle to the accident site. He estimated that he arrived within two minutes of the accident, to find that the helicopter’s occupants had escaped, without injury, and that the helicopter operator did not believe there was a fire risk, so the local emergency services were not alerted. Helicopter operator’s investigation The helicopter operator conducted an internal investigation which concluded that the accident could have been avoided if the pilot of G-CTFL had turned the tail of his aircraft and visually checked the area behind. The operator considers such a lookout turn to be a 65 ©Crown copyright 2018 All times are UTC AAIB Bulletin: 10/2018 G-CTFL and G-HYND EW/G2018/05/07 standard procedure before a helicopter is moved rearwards, but the pilot felt constrained from moving the tail of his helicopter left by the presence of spectators. However, the CCTV recordings showed nobody on the roadway or grass area immediately to the left of G-CTFL and the helicopter operator believed the tail could have been moved left, leaving a 5 m safety margin from any people or obstructions. According to the helicopter operator, it was not unusual for helicopters to reverse from the southern helipad, if the other pad was occupied and Apron A congested. The helicopter operator reported that its checklist for the R44 shutdown procedure does not clearly specify when the avionics should be switched off, so it was not unusual that the pilot of G-HYND had switched the radio off and removed his headset once the engine had stopped but with the rotors still turning. Helicopter operator’s safety actions As a result of the accident, the following safety actions have been taken by the helicopter operator: ● The northern helipad was extended eastwards by 12 m, so a parked helicopter is further from the apron, leaving space for other helicopters to move between the parked helicopter and the apron. ● The prepared grass area east of the helipads has been extended, to ensure helicopters parked there can remain well clear of the pads. ● A mirror has been placed at the corner of the hangar, to assist pilots using either helipad see any activity to their rear. ● The helicopter operator no longer permits helicopters to reverse from the helipads. ● The helicopter operator’s safety team is due to review the procedure for turning off the avionics systems while a Robinson R44 is being shut down. ● A review of the RFFS response to this accident has led to several changes being instigated. These are intended to ensure that two appropriately trained employees are available, on the ground, at all times there is helicopter activity and that fire-fighting equipment can be readily accessed by these employees. Airport operator’s report An investigation by the airport operator established that immediately after the accident it would have been best to close the airport until appropriate inspections of the manoeuvring area and Apron A had been completed. Scrutiny of the airport’s emergency procedures following this accident highlighted some ambiguities and the operator undertook to review and revise the relevant guidance as necessary. 66 ©Crown copyright 2018 All times are UTC AAIB Bulletin: 10/2018 G-CTFL and G-HYND EW/G2018/05/07 AAIB comment The collision between the two helicopters occurred because the pilot of G-CTFL was not aware of G-HYND’s position. However, the damage to G-CTFL did not appear to immediately effect the operation of its engine or flying controls. The pilot of G-CTFL stated that he recalled his helicopter pitching nose-up and he made a forward cyclic input in response, but CCTV showed that after hitting G-HYND’s rotor blade, G-CTFL pitched nose-down. An excessive nose-down attitude ensued, close to the ground, before recovery action appears to have been initiated and the nose began to pitch up. However, the helicopter was now descending towards the helipad and, as the nose pitched up, the tail struck the ground and initiated the impact sequence. It is likely that the pilot of G-CTFL was startled by the unexpected collision with the other helicopter. The ‘startle effect’1 is likely to have impaired his ability to comprehend the situation and also his psychomotor skills, leading to his loss of control. When the helicopter operator’s employees responded to the accident they did not take any fire fighting equipment to the scene, so it was fortuitous that there was no outbreak of fire before all the helicopters’ occupants escaped. As a result, emergency response procedures have been changed, but this accident highlights the need to regularly review such procedures. Footnote 1 Startle is defined in the Federal Aviation Authority’s Advisory Circular 120-111 of 2015 as ‘an uncontrollable, automatic muscle reflex, raised heart rate, blood pressure, etc., elicited by exposure to a sudden, intense event that violates a pilot’s expectations.’ An overview of the ‘startle effect’ and details of reference material can be found on the SKYbrary website at https://www.skybrary.aero/index.php/Startle_Effect (accessed September 2018)