What happened
On June 22, 1991, an A-122B Uirapuru, registration PP-HSL, departed from the Pará de Minas Aerodrome for a local recreational flight. Shortly after takeoff, at an altitude of approximately 300 feet, the engine suffered a sudden shutdown. Following the loss of power, the aircraft entered a right-hand turn and began losing altitude. In an attempt to execute a forced landing, the crew maneuvered toward an area that was not reachable, resulting in an uncontrolled stall. The aircraft struck the ground at a steep angle, impacting the terrain twice before coming to a rest. The impact resulted in the fatalities of both pilots and the total destruction of the aircraft.
The investigation
CENIPA investigators examined the engine, fuel systems, and cockpit controls to determine the cause of the sudden power loss. Technical analysis of the Lycoming engine and its accessories revealed no internal mechanical failures. Furthermore, fuel samples from the tanks, carburetor bowl, and fuel filter showed no signs of contamination or impurities.
Investigation of the cockpit switches provided a critical clue: the magneto switches were found broken at the base in the "off" position. Because the landing lights switch is located immediately adjacent to the magnetos and uses a similar movement, investigators concluded that a crew member likely intended to turn off the landing lights but inadvertently switched off the magnetos. This accidental shutdown occurred at a critically low altitude, leaving insufficient time to recover.
Findings
- Accidental Magneto Shutdown: The primary cause of the engine failure was the unintentional turning off of the magnetos while attempting to operate the landing light switches.
- Loss of Control: The crew attempted to reach a landing site that was outside of the aircraft's gliding range, leading to an excessive pitch and bank that induced a stall.
- Inadequate Experience: Both crew members had very limited experience in the A-122B Uirapuru; the aircraft had been grounded for five months prior to the accident.
- Human Factors: The pilot demonstrated a history of poor concentration and insufficient technical proficiency, having previously been restricted from solo flight in this type. The co-pilot, acting in a supervisory capacity, failed to maintain sufficient situational awareness to intervene during the critical phase of flight.
- Organizational Oversight: The aeroclube failed to provide adequate training or supervision for a pilot with known deficiencies and did not ensure proper currency for the instructor following the aircraft's long period of inactivity.