1966 Agusta-Bell 47J-3B-1 Helicopter Accident at Bannalp (HB-XBX)

Accident Overview and Investigation Status On 25 September 1966, an Agusta-Bell 47J-3B-1 helicopter, registration HB-XBX, was destroyed during a rescue operation on the Bannalp in the canton of Nidwalden, Switzerland. The Swiss Federal Accident Investigation Commission approved its investigation report on 23 March 1967, with circulation noted on 23 April and 6 May 1967. The report identified a similar earlier case involving HB-XBT near Amden on 12 October 1963. ## Aircraft, Pilot, and Operational Context The helicopter was owned and registered to Schweiz. Helikopter A.G., Bern. It was a multi-purpose helicopter with a shell fuselage, semi-rigid two-blade main rotor, tail rotor for torque compensation, and skid landing gear. Its Lycoming TVO435-B1A engine was rated at 270 hp. The aircraft had been imported new into Switzerland on 13 July 1964. Its airworthiness approval was issued on 31 July 1964 and valid until 1 October 1967. The pilot was born in 1942 and held a professional helicopter pilot licence issued on 11 January 1965, valid until 31 October 1966, with a Bell-47J type rating and a mountain off-landing extension dated 24 June 1965. He had begun powered flight training in Bern on 4 July 1960 and helicopter training on 9 November 1964. Since spring 1965, he had been employed by Heliswiss. His total experience was 910 flight hours and 5,000 landings, including about 660 hours and 4,000 landings on helicopters, with approximately 60 hours on the accident type. No accidents, incidents, or regulatory violations were recorded against him, and the investigation found no indication that he was in poor health on the day of the accident. ## Flight Details and Rescue Operation The accident occurred at 1730 local time. The Swiss Air Office duty service notified the accident investigation office the same evening. A preliminary investigation was opened the following day at 1630 at the accident site, in cooperation with the Nidwalden cantonal police. The helicopter had been tasked by the Swiss Air Rescue Service (SRFW), which had been alerted around 1530 by the Nidwalden cantonal police after a report that a tourist had fallen on the Bannalp and suffered a painful leg fracture. The pilot departed Bern at 1619 and arrived at the Bannalp 40 minutes later. Two cantonal police officers had prepared a landing site on the crest of the Bannalpsee dam. After landing, the pilot learned that the injured person’s exact location was still unknown. He then took one police officer on a search flight and, after about 15 minutes, located the injured tourist in a steep scree slope at the foot of the Bannalpnadel. Because the terrain offered no landing site, the pilot set the officer down in a hover near the injured person and returned to the dam to pick up the second officer, setting him down in the same manner. The pilot then landed on a nearby alpine meadow about 400 m below the accident site. As time was running short, the pilot decided to lift the injured climber into the helicopter in flight. To make it easier for the rescuers to slide the stretcher into the cabin, he removed both doors and took off shortly before 1730 for the actual rescue. ## Accident Sequence and Damage While hovering at the accident site, the pilot approached the rescuers laterally and parallel to the slope. The injured person was ready for transport on a stretcher. As the pilot was about to rest the right skid on a rock slab, he heard a loud crackling noise. The helicopter suddenly turned 45° to the left, tilted downslope, and burst into flames. The burning wreckage came to rest on its back, wedged between rocks about 30 m lower down. The pilot, who had remained strapped in his seat, managed to unbuckle and escape through the shattered front windshield. The pilot sustained a spinal injury and burns to his arms and head. His hospital stay lasted four weeks, and he was unable to work for two months. He reached the Hotel Bannalp on foot without assistance, where he received initial medical care. The injured tourist, born in 1924, was recovered the same evening by a 15-person rescue column and taken to a clinic in Lucerne. The helicopter, valued at approximately CHF 320,000, was destroyed. No other persons or property were damaged. ## Findings and Probable Cause The accident occurred at the moment the pilot placed the right skid on the outer edge of a rock slab about 2 m high and 2.5 m wide. The exact point of skid contact was determined from small paint fragments. Above the slab, the terrain rose at about 100% up to the height of the main rotor, and about 60% above that. Examination of the scree at rotor height revealed metal deposits on the rock, tangential to the rotor circle, in the form of two horizontal lines 6 cm and 15 cm long and 3–5 mm wide. The investigation concluded that the crackling heard by the pilot was caused by the main rotor blades striking the rock. The resulting rotor braking caused an immediate change in engine torque, producing the rapid yaw of the fuselage. The pilot reported that the helicopter had operated normally during the overflight and in the operational area, and there were no adverse visibility or wind conditions. The rotor ground contact was attributed solely to the pilot approaching too close to the slope, either by overestimating the available clearance for the rotor or by becoming too preoccupied during the approach and not paying sufficient attention to the terrain at rotor height. The accident was caused by the pilot losing control of the helicopter after the main rotor struck rock while attempting to take on board an injured climber in a hover at the slope; the helicopter overturned and caught fire.