Introduction
On 5 June 1960, at 10:51 local time, a Piper PA-22 Tri-Pacer (registration HB-OPA) departed from Locarno Airport for an aerial competition. The pilot was accompanied by his wife. The flight proceeded normally until the return near Locarno, when the pilot intended to enter a right turn to prepare for landing. Instead, the aircraft began a descending left spiral, first wide then tightening, crossing over Ascona Airport. At 11:11, it struck the ground 120 meters east of Ascona Airport. The aircraft was destroyed; the pilot and his wife sustained minor injuries.
Investigation
The investigation was detailed and took considerable time. The pilot held a private pilot license issued in August 1959 and had accumulated 72 hours and 28 minutes of flight time, with 10 hours and 51 minutes on the accident aircraft type. He had a pre-existing condition: ankylosis of the left knee joint, resulting in a stiff leg in an extended position. Despite this, he was deemed fit to fly after a medical examination and instructor certification that he could operate the rudder. The transition to the PA-22 was made without difficulty, though the instructor noted a slight impediment.
Aircraft
The Piper PA-22 Tri-Pacer, serial number 22-2532, was a four-seat aircraft with a Lycoming O-320 engine producing 150 hp. It had a maximum takeoff weight of 907 kg; the flight weight at the time of the accident was 750 kg, within limits. The aircraft was equipped with interconnected aileron and rudder controls, requiring coordinated use. Technical examination found no pre-existing deficiencies, including in controls and engine. However, test flights under similar conditions revealed possible engine stoppage when using the right fuel tank during a left skidding turn.
Flight and Accident
The pilot departed at 10:51 after a previous competitor had used the aircraft for 33 minutes on the left fuel tank and advised using the right tank. During the competition flight, the pilot and his wife answered all questions except one about the statue of San Carlo. They assumed the breviary was in the left hand. At about 11:05, at an altitude of approximately 550 meters above the Maggia delta, the pilot reduced speed for landing at Locarno. He intended a slight right turn but the aircraft reacted with a left skid. He briefly released the controls, reducing the skid but not stopping it. He then attempted a decisive right turn; the aircraft banked slightly right but maintained direction with a strong tendency to skid left. Choosing to land at Ascona, he applied left rudder, and the aircraft headed toward Ascona. At about 200 meters altitude, the engine stopped briefly. After applying carburetor heat, it ran for a few seconds, then stopped again. He turned off carburetor heat and switched fuel tanks. The aircraft crossed Ascona Airport diagonally, and realizing a forced landing was necessary, the pilot prepared for a landing off the field. The engine resumed, but his attention was on trees. Just before impact, he turned the control wheel fully right and pulled back on the elevator.
Cause
The accident was probably caused by the pilot, hindered by a pre-existing ankylosis of the left knee joint, involuntarily and unconsciously crossing the rudder and ailerons when initiating the turn. He failed to recognize the resulting flight attitude and did not correct it.