Introduction
On 4 August 2018, the historic Junkers Ju 52/3m g4e, registered HB-HOT and operated by Ju-Air, departed Locarno Aerodrome (LSZL) at 16:14 for a commercial VFR flight to Dübendorf (LSMD). The commander, seated in the left cockpit seat, piloted the aircraft, while the co-pilot assisted from the right seat.
Flight History
After takeoff from concrete runway 26R, the aircraft turned 180 degrees over Lake Maggiore and entered the Blenio valley via Bellinzona and Biasca, steadily gaining altitude. North of Olivone, it turned into the Lago di Luzzone reservoir valley, crossing the Adula/Greina/Medels/Vals quiet zone at 120–300 m above ground with minimal lateral terrain clearance. At 16:45, over Alp Nadels, an ISP text message informed a friend that the Ju 52 was approaching. The flight continued eastwards into the Surselva region at about 2,500 m AMSL. At 16:51, it crossed the Vorderrhein valley near Ilanz on a northeasterly heading, making a tight left turn over Ruschein. The path then led northwards past Crap Sogn Gion toward the basin southwest of Piz Segnas. The aircraft climbed to 2,833 m AMSL near Nagens, then made a slight right turn past Berghaus Nagens lodge. At 16:55, a pilot informed passengers of the scenery via cabin speakers. Ground speed initially was 165 km/h, decreasing to 135 km/h by point F2, roughly maintained until before point F3. Toward F3, altitude dropped slightly and ground speed briefly increased to ~200 km/h; pitch attitude was 5–7 degrees. Just before point F4, flight path angle changed from -3 to -1 degree, and engine speeds decreased by ~20 rpm each. At point F4, altitude was 2,742 m AMSL. At 16:56:02, engine speeds increased by ~40 rpm each. At 16:56:09, HB-HOT entered the basin southwest of Piz Segnas at 2,755 m AMSL, ~130 m above Segnes pass elevation. The crew navigated north-northeast near valley center. The aircraft climbed slightly with flight path angle ~2 degrees and pitch 5–7 degrees. At 16:56:17, altitude reached 2,767 m AMSL at point F7, ~140 m above the pass. As it passed the Tschingelhörner peaks, altitude dropped more than 15 m in 6 seconds. Engine power was rapidly reduced by 30–50 rpm, bringing engines to similar speeds. Pitch angle increased and flight path angle became more negative. Approaching Martinsloch at 2,766 m AMSL (point F8), the crew initiated a right turn in descent, followed by a left turn (point F9–F10). Ground speed was ~170 km/h; the difference between pitch and flight path angles reached ~15 degrees during the right turn. Transitioning to left turn, pitch was ~11 degrees and flight path angle ~ -10 degrees, at ~125 m above Segnes pass. Over the next 4 seconds, the aircraft descended 25 m and the negative flight path angle steepened. After point F13, left roll increased steadily despite significant right aileron deflection. Ailerons were neutralized and temporarily deflected for left turn. Pitch attitude decreased, flight path steepened downward, and left bank increased. Low-frequency vibrations occurred during this phase. At 108 m above ground (point F16), the longitudinal axis pointed 68 degrees downward from horizontal. Elevator had deflected upward ~13 degrees, rudder 2 degrees right. Engine speeds had increased slightly to 1,720–1,750 rpm. Roll to the left accelerated. Shortly after 16:57, the aircraft struck the ground in a near-vertical attitude at ~200 km/h. All 20 occupants died. The aircraft was destroyed; no fire occurred. Reconstructions showed the center of gravity was 2.071 m behind the wing leading edge. Images from inside showed no movement or occupants out of seats from entry into the basin until the start of the downward spiral.
Probable Cause
The official investigation determined the direct cause: after losing control, there was insufficient space to regain control, leading to collision with terrain. Direct causal factors included the flight crew piloting the aircraft in a very high-risk manner by navigating into a narrow valley at low altitude with no alternative flight path, and choosing dangerously low airspeed relative to the flight path, such that expected turbulence led to a short-term stall, loss of control, and an unrectifiable situation. Directly contributory factors were the crew's habitual non-compliance with safe flight operations rules and high-risk taking, and an operating center of gravity beyond the rear limit, which facilitated loss of control. The systemic cause involved inadequate organizational safety management.