Flight History
The pilot planned a multi-day holiday trip to the Netherlands in the Socata TB10 registered HB-EZW. Four days before departure, the chief flight instructor of the Motorfluggruppe Pilatus recommended by email that the pilot perform a circuit to re-familiarize with the aircraft's handling. On the evening before the flight, the pilot filed a flight plan to Basel (LFSB). On the morning of 4 August 2018, the pilot fueled the aircraft for a total endurance of about three hours. The four occupants boarded: the pilot in the left front seat, a child in the right front, and the pilot's wife and another child in the rear seats.
At 09:44 LT, the aircraft taxied to the holding point of Runway 03 at Kägiswil. After a run-up, the pilot broadcast a blind transmission at 09:45 indicating intention to taxi into position and take off. The aircraft rolled onto Runway 03 and became airborne at 09:46 after a takeoff roll of approximately 450 meters. After lift-off, the aircraft climbed with a ground speed of about 70 kt and a rate of climb of roughly 400 ft/min. It overflew a crane north of the runway end and turned right to a heading of about 60°, following the Sarneraa River northeastbound.
At 09:47:28, the pilot made another blind transmission stating intention to fly via Lopper towards Emmen. The aircraft was then at approximately 1910 ft AMSL with a ground speed of 79 kt and a climb rate of about 220 ft/min. After reaching Lake Alpnach, the aircraft turned north towards the crest of the Renggpass while continuing to climb. As it approached the ridge, ground speed decreased to around 70 kt with an average climb rate of about 300 ft/min.
Accident Sequence
Witnesses observing the approach to the Renggpass from close range heard a normal engine sound. At 09:50 LT, while in a climb, the HB-EZW struck tree tops at the northern end of the Schoffel field on the crest of the Renggpass at approximately 900 m/M (2953 ft AMSL). The impact separated parts of the right wing's leading edge. Subsequently, the aircraft descended in a steep right-hand spiral almost vertically. Witnesses perceived a delayed engine surge. About 200 meters lower, the aircraft struck the forest floor on the north slope at an elevation of 715 m/M and caught fire. All four occupants sustained fatal injuries in the impact. The emergency locator transmitter activated. No further radio transmissions were recorded aside from the two brief blind broadcasts.
Aircraft Information
The Socata TB10 Tobago is a single-engine, four-seat low-wing metal aircraft with fixed tricycle landing gear. It was owned and operated by the Motorfluggruppe Pilatus. The airframe had accumulated 5492:01 hours TSN; the engine (Lycoming O-360-A1AD) had 1137:54 hours TSO; the propeller (Hoffmann 3-blade HO-V 123K-K) had 419:17 hours TSO. Weight and balance were within limits. The last 100-hour inspection occurred on 17 July 2018 at 5473:92 TSN. The aircraft was equipped with a sound-dampening system (STC TB10-606500) that did not affect performance.
According to the Aircraft Flight Manual, maximum rate of climb is achieved at VY (78 KIAS) with a pitch attitude of 12.7° above horizon at sea level; best climb angle at VX (62 KIAS) gives 6.6° with pitch attitude 19.8°. The density altitude at the accident time and location was about 4700 ft AMSL, reducing climb performance by about 8%. The maximum available rate of climb at maximum takeoff mass was thus approximately 600 ft/min.
Pilot Information
The pilot, a Swiss national born in 1971, held a Commercial Pilot Licence (CPL(A)) issued by the Federal Office of Civil Aviation. His total flight experience was about 8040 hours, with roughly half on single-engine turbine aircraft. In the last two years before the accident, he had logged 10 hours on single-engine piston aircraft, none on the accident type. He was familiar with the local topography.