Accident Overview
On Sunday, 24 May 1959, the pilot of a Jodel D-117 (registration HB-SOO) departed from Hasenstrick airfield with his son as a passenger. Due to uneven grass growth, the pilot did not align exactly with the runway axis but deviated at a shallow angle of approximately 5° to the left. After a takeoff run of about 200 meters, immediately after liftoff, the tail of the aircraft struck an iron barrel located just outside the runway edge. The impact destroyed the rudder mounting, causing a loss of controllability. At a height of about twenty meters, the aircraft banked to the right and then descended steeply, impacting the ground. Both occupants sustained serious injuries and the aircraft was heavily damaged.
Aircraft and Occupants
The pilot, born in 1906, held a private pilot license issued on 29 May 1929, valid until 21 October 1959. He had accumulated 1519 hours and 32 minutes of flight time over 1844 flights. He was well acquainted with the accident aircraft, having flown it exclusively in 1958/59. The passenger, born in 1935, was the pilot's son and held a student pilot permit valid until 29 April 1961.
The aircraft was a Jodel D-117, a single-engine, two-seat low-wing wood construction aircraft, built in 1958 (serial number 858-11). It was powered by a Continental C-90-12F engine (90 hp) with a Mc Cauley propeller. The maximum takeoff weight was 620 kg; the weight at the time of the accident was about 580 kg, and the center of gravity was within limits. Total operating time was 189 hours and 32 minutes. No pre-existing airworthiness issues were found.
Airfield Conditions
The accident occurred during takeoff from runway 11 at Hasenstrick airfield, which was classified as a K-class field requiring a minimum runway length of 300 m and width of 30 m. The operating permit was issued to the Flugsportgruppe Zürcher Oberland on 30 July 1954. However, at the time of the accident, the airfield did not meet several regulations and requirements:
- The runway width was only 20 m instead of the required 30 m.
- The grass runway was not fully mowed: the southern part had high grass on a 200 m by 5 m area, the middle part had medium grass on a 100 m by 10 m area, and only the remaining section was fully mowed.
- Two red-and-white iron barrels marking the airfield boundaries were located near the runway markers at the 200 m and 300 m points.
- The runway surface, especially the northwestern part, was uneven; only an 8-10 m wide strip along the centerline was in good condition.
Several days before the accident, a farmhand had moved the two iron barrels from their usual positions closer to the runway during mowing. The airfield manager noticed them at least during his own flight on the day of the accident but took no action to move them back, considering them as useful markers for a bump.
Weather
At the time of the accident, weather was good: 7/8 cloud cover with base at 1600 m, visibility 20-25 km, light northeast wind.
Flight Sequence
On the morning of the accident, the pilot was at Speck airfield where his aircraft was based. Around noon, he flew as a passenger in a Sokol to Hasenstrick to see that aircraft type. After a short stop, they returned to Speck without issues. Later, he flew to Zurich and back to Speck. Around 1600, he decided to fly again to Hasenstrick with his son. He called the airfield manager, who confirmed the field was open. The pilot had previously received the required special briefing for using the field. They landed at 1618 on the mowed part of the runway. During landing, the pilot noted that the southern part of the runway still had grass and saw a rectangle of medium-height grass near the end; he felt the field was somewhat constricted. After landing, he parked and briefly spoke with the manager and another pilot, but runway conditions were not discussed. After about half an hour, they reboarded.
The pilot took the left seat and taxied for takeoff. Instead of using the centerline with medium grass, he chose a direction slightly to the left, toward the mowed section of the field, heading roughly toward the northeastern end. Takeoff began at 1654. The direction was exactly toward the iron barrel at the runway edge, which the pilot had not noticed earlier. Due to the terrain, the barrel only came into his field of view later, and he did not spot it before liftoff. Takeoff was slightly delayed by ground unevenness, causing small bounces. Just before liftoff, the passenger saw the barrel and shouted. The pilot then tried to climb over it but did not entirely succeed; the tail struck the barrel at a speed of 55-60 km/h and at about 50 cm above the ground in a shallow climb. The impact tore off the tail wheel spring assembly and the rudder mounting. The rudder was then held only by its control cables, rendering directional control impossible and severely affecting elevator effectiveness. The aircraft continued climbing to about 20 m above the ground at the runway end. Witnesses on the ground observed a sharp reduction in engine power, then the aircraft banked to the right and entered a right turn with increasing descent angle until impact.
Damage
Both occupants sustained severe fractures and other injuries. The pilot required nearly five months of hospitalization, his son two months, followed by long outpatient treatment. Both retained permanent minor walking impairment. The aircraft was heavily damaged.
Investigation Findings
The investigation revealed that the airfield and its operation did not comply with regulations and requirements in several respects. The immediate technical cause of the accident was loss of controllability due to damage to the rudder from collision with an obstacle.