What happened
On May 17, 1998, a CAP-4 aircraft, operated by Aeroclube de Lavras, took off from Lavras Airport (SNLW) for a local scenic flight. The aircraft was carrying the pilot and two passengers, including a child seated on an adult's lap. Shortly after takeoff, the engine suffered a sudden loss of power and subsequently stopped.
In an attempt to return to the runway, the pilot initiated a steep left-hand turn at a very low altitude. During this maneuver, the aircraft entered a stall and collided with the ground, with the left wing striking the terrain first. The impact caused significant damage to the landing gear, left wing, fuselage, and engine, and rendered the propeller unserviceable. The pilot sustained minor injuries due to striking the instrument panel, while the passengers remained uninjured.
The investigation
CENIPA investigators examined the aircraft's electrical system and maintenance history. The investigation revealed that during a previous 100-hour inspection, maintenance personnel failed to notice that several wires connected to the magneto switch box lacked proper insulation. Specifically, a junction was found without the required connection or insulation, and silicone had been used as an improvised insulator on the metal box. This lack of insulation allowed a wire to contact the metal components, causing a short circuit that led to the engine failure.
Investigators also reviewed operational practices at the aeroclube. It was noted that the aircraft was being operated in violation of its maximum capacity, as the manual specifies a limit of one passenger in the rear nacelle. Additionally, the pilot was flying without using the safety harnesses (suspenders) due to a known equipment failure, a practice that was common at the club.
Findings
- Electrical Short Circuit: An uninsulated wire made contact with the magneto switch box, causing a short circuit and subsequent engine failure.
- Improper Maintenance: The 100-hour inspection failed to identify the improper insulation of the magneto wiring.
- Inadequate Emergency Technique: The pilot attempted a return to the runway via a steep turn rather than following the recommended procedure for low-performance single-engine aircraft, which is to land straight ahead.
- Operational Non-compliance: The aircraft was carrying an unauthorized passenger load (a child on an adult's lap) and was being operated without functional safety harnesses.
- Organizational Culture: A lack of proactive safety culture at the aeroclube permitted non-standard operating procedures and complacent attitudes regarding safety equipment.