What happened
On January 31, 2002, an RH-22 helicopter, registration PT-YNI, was conducting flight instruction at the Guarapiranga ultralight airfield in São Paulo, Brazil. The flight, operated by Tecplan Escola de Pilotagem, involved an instructor and a student performing a 180-degree autorotation maneuver. During the second attempt of the exercise, the crew was unable to recover the aircraft's rotation through engine power application, leading to a collision with the terrain.
The impact was forceful and aligned with the aircraft's direction of travel. The collision caused the main rotor to strike the tail boom. The aircraft sustained severe damage to the engine, main and tail rotors, transmission, cockpit, and landing skids. Despite the severity of the impact, both the instructor and the student escaped the wreckage uninjured.
The investigation
CENIPA's investigation focused on the sequence of events during the maneuver and the pilot's decision-making. Investigators examined the aircraft's maintenance records, which were found to be up to date, and the crew's credentials, confirming both pilots held valid licenses and medical certificates. The instructor was found to have sufficient experience for the flight.
The analysis determined that the engine power was applied too late and at an insufficient altitude to maintain the necessary rotor RPM. This resulted in a low-altitude rotor stall. As the helicopter descended, the airflow caused the rotor disk to tilt backward—a phenomenon known as "rotor blow-back"—which led to the main rotor blades striking the tail boom.
Findings
- Inadequate altitude for recovery: The instructor failed to initiate the power application early enough to ensure sufficient rotor RPM.
- Improper flight planning: The instructor failed to account for environmental factors, specifically temperature and aircraft weight, which necessitated an earlier start to the recovery phase.
- Deficient judgment: The instructor's decision to delay the recovery maneuver prevented the engine from meeting the energy demands required to sustain the rotor's high angle of attack.
Safety action
Following the investigation, safety recommendations were issued to flight schools to standardize the altitude for autorotation recovery and to ensure instructors emphasize the specific timing of engine application during student briefings. Additionally, a special safety inspection was conducted at the flight school involved.