What happened
On May 12, 2003, a Schweitzer 269C-1 helicopter, registration PP-MAV, was conducting a local flight instruction mission near the Helipark helipad in Carapicuíba, Brazil. During a series of approach and landing maneuvers, the crew experienced a sudden left yaw, which the instructor interpreted as a momentary engine failure.
Following this initial disturbance, the instructor increased altitude and decided to return to the Helipark helipad to better evaluate the situation. During the subsequent final approach, as the pilot lowered the collective to reduce power, the engine ceased operation entirely. The crew attempted an autorotation, but the aircraft struck the ground with the tail rotor first, followed by the skids. Both the instructor and the student survived the impact uninjured, though the aircraft sustained severe damage to the main rotor, transmission, structure, and tail rotor.
The investigation
CENIPA investigators examined the engine and fuel systems, finding no mechanical discrepancies or impurities in the fuel line that could have caused a failure. Testing performed on a test bench showed the engine was operating normally according to specifications.
The investigation focused on environmental conditions and operational procedures. On the day of the accident, the weather was characterized by low temperatures and high humidity, conditions highly conducive to carburetor icing. Investigators also scrutinized the training practices of the operator, Edra Aeronáutica Ltda., regarding the use of the carburetor heat.
Findings
- Carburetor icing was the primary cause of the engine failure. The instructor had been trained to avoid using the carburetor heat when operating below 18 inches of manifold pressure, a practice that contradicted the manufacturer's recommendations.
- The decision to activate the carburetor heat during the flight likely caused ice to break loose and obstruct the fuel flow, eventually leading to the complete engine shutdown when the throttle was reduced.
- The instructor's judgment was flawed regarding the decision to return to the helipad instead of performing an immediate landing at the training site upon noticing the first signs of engine instability.
- A lack of management supervision at the flight school allowed incorrect instructional procedures—specifically the improper use of carburetor heat—to persist and be passed down to students.