Swiss investigators have concluded that pilot of a Piper PA-28 handed control to a 14-year old enthusiast during a pleasure flight before the aircraft fatally crashed in the Alps near the Italian border.

Four occupants had been on board the PA-28, which had been conducting a flight from Samedan airport, as part of a week-long summer aviation youth camp run by Aero-Club of Switzerland.

Some 200 young people attended the event and three, all teenagers, had accompanied the PA-28 pilot on the 4 August 2017 flight.

While the trip through the mountainous area was intended as a flying experience, Swiss investigation authority SUST found that, during such flights, the passenger in the right-hand front seat would often be offered the chance to “feel” the aircraft, or even take control.

SUST points out that this practice occurred despite the supervising pilot’s not having instructor qualifications.

Transferring control of the aircraft to someone who had no pilot training entailed a “considerable risk”, it says, particularly given the challenging nature of the flight.

But it stresses that the passenger “cannot be blamed” for seizing the opportunity to fly an aircraft for the first time, adding that he had been acting in accordance with the pilot’s instructions.

The PA-28 (HB-PER) had been part of a two-aircraft formation with a Cirrus SR22, and both had been following a course from Samedan airport, near St Moritz, south-east through a mountain pass towards Diavolezza.

In the vicinity of Pontresina the passenger was handed control of the aircraft, according to the only survivor of the crash, a youth sitting in the left-hand rear seat.

The aircraft climbed towards 9,000ft and passed the lower station of the Bernina-Diavolezza cable car, at which point the pilot signalled to the flying passenger to start a left turn.

SUST says the aircraft commenced a climbing three-quarter turn, exiting at 9,200ft, and heading south-south-west towards higher terrain. It crossed the lake Lej da Diavolezza and passed east of a 9,524ft peak known as Corn Diavolezza, at a height of 25m (82ft) above terrain and a speed of 63kt.

The pilot told the passenger to head for the upper station of the cable car, which was ahead of them, and the aircraft passed over a chairlift pylon with a height margin of 20m.

Weather conditions were calm, says the inquiry. But the PA-28 commenced a steeply-banked "sharp and fast” turn to the right, losing height and passing under the cable car line and struck the ground with its starboard wing. The altitude of the impact was around 9,400ft.

While the aircraft was within balance limits, it was heavily-laden, operating at 1,075kg – about 93% of its maximum take-off weight. Analysis also showed that the air temperature at 9,500ft was relatively high, around 11°C, and that the density altitude equated to 10,520ft. This reduced the aircraft’s climb performance by around 27% compared with standard atmospheric conditions.

Mountain flying, says SUST, requires the pilot to view the flightpath as a series of stages, ensuring the aircraft has an escape route, and sufficient manoeuvring capability, if it is unable to proceed from one stage to the next.

The inquiry sharply criticises the planning aspect of the PA-28 flight, describing the pilot’s decisions as “risky” with “significant errors” given the terrain, the presence of obstacles such as cables, and the aircraft's diminished performance.

SUST says there was a “lack of safety awareness” by the organisers of the flights, which allowed pilots to entrust the aircraft to inexperienced individuals.

Aero-Club of Switzerland says it remains “deeply affected” by the accident and will study the SUST inquiry findings to “analyse the implications”, and decide how to handle future flights at youth camps.