Introduction
On Saturday, 23 May 1964, at 1609 local time, a Caravelle SE-210 (YU-AHA) departed from runway 10 at Zürich-Kloten Airport. Half a minute later, a student pilot flying a Piper Cub J3C (HB-OEN) on a training exercise was performing touch-and-go landings on the parallel grass runway. During the final approach, the Piper Cub suddenly rolled right, entered a knife-edge attitude, and veered toward the light aircraft parking area. While rolling out, it struck a parked Norécrin II (HB-DAG). No persons were injured. The Piper Cub sustained substantial damage; the Norécrin sustained minor damage.
Aircraft and Personnel
The Piper Cub J3C (HB-OEN) was a single-engine, two-seat high-wing monoplane with a Continental A-65 engine, built in 1943. It was owned by the motor flight group of the Zurich section of the Swiss Aero Club. The student pilot, born 1918, held a learner's permit since 30 March 1961 and had 56 hours 24 minutes total flight time with 357 landings, mostly on the accident type. He was near the end of his training for a private pilot license, which he later passed. The flight instructor, born 1927, had a professional pilot license and extensive experience. The Caravelle was operated by JAT Yugoslav Airlines. The Norécrin was privately owned.
Flight Sequence
On the day of the accident, the student was practicing spot landings solo under the supervision of the flight instructor, who was monitoring from the ground. The grass runway 10, 500 meters long, lay parallel and south of the concrete runway 10, with its threshold 1750 meters from the concrete runway threshold. The light aircraft parking area was 220 meters from the grass threshold. At 1556, the student took off for the first flight; after a long landing, he took off again at 1600 for a second flight, assigned a spot landing from 600 feet with a left sideslip. Noticing the Caravelle preparing for takeoff on the concrete runway, the student delayed his first 90-degree turn into the landing pattern. During the turn, he observed the Caravelle starting its takeoff at 1609. He continued his approach, checking for the red point signal that would prohibit landing. The instructor considered displaying the signal but decided against it due to crosswind and expected time delay. The student performed the second 90-degree turn, aligned with the runway, and entered a sideslip. The Caravelle, having taken off normally and lifted off about 300 meters before the runway controller's position, was no longer observed by the student. He ended the sideslip and began to flare at 5 to 10 meters altitude when his aircraft abruptly rolled right into a knife-edge attitude. He temporarily lost control; the aircraft executed an unintended 90-degree right turn with full left control input and engine at idle. He regained control at low altitude and landed on the taxiway in front of the parking area. Despite heavy braking and a slight left turn, he collided with the parked Norécrin while rolling out at about 1610.
Damage
The Piper Cub (HB-OEN) sustained heavy damage to the right wing and light damage to the rest of the airframe and engine, estimated at 20% of value. The Norécrin (HB-DAG) had its right wing leading edge crushed, estimated at 5% of value. No persons were injured.
Probable Cause
According to the investigation, the accident was due to the student pilot flying too close behind the departing airliner, entering its wake turbulence on final approach, and temporarily losing control of his aircraft.
Investigation
The investigation determined with near certainty that the accident resulted from the landing aircraft encountering the wingtip vortices of the airliner that had just taken off from the parallel runway. The vortex from the airliner's left wing intersected the flight path of the Piper Cub. The risk was exacerbated by the proximity of the final approach path for light aircraft and the start of the airliner's climb. The instructor, given his experience, could assess the situation from the ground, and the student's training level also placed responsibility on him. A holding pattern would have been advisable.