What happened
On July 8, 2016, a Robinson R22 helicopter, registration PT-YDP, was conducting a navigation training flight. The flight originated at Aeródromo de Juiz de Fará, MG, and included several intermediate stops at Ubatuba, Parati, and Juiz de Fora, before the final leg toward the Helicentro BH helipad in Nova Lima, MG.
During the final approach to the helipad, the aircraft experienced an increased rate of descent. Despite the pilot increasing torque by adjusting the collective pitch, the main rotor RPM dropped. While the drop was not severe enough to trigger the low RPM warning horn, the loss of power caused the aircraft to lose stability. The pilot experienced a right-hand roll tendency and attempted to correct it with maximum pedal and cyclic input to the left. Ultimately, the aircraft performed a hard landing on a grassy area just before the intended landing pad, resulting in light damage to the aircraft. Both occupants were uninjured.
The investigation
CENIPA investigators examined the engine components and maintenance records of the PT-YDP. The investigation revealed that the aircraft had experienced engine starting difficulties earlier in the day at both Itanhaém and Paraty, requiring the use of a second battery to successfully start the engine.
Upon inspection of the engine, investigators removed all spark plugs and discovered significant fuel residue accumulation, corrosion, and excessive electrode wear. Testing with specialized equipment confirmed deficient sparking, specifically noting that the spark plug from cylinder number 3 failed to produce any spark at all. Furthermore, testing of the magnetos revealed a lack of synchronization and improper timing offsets compared to the manufacturer's standard specifications.
Maintenance records indicated that while a 100-hour inspection had been performed in December 2015, there were no records of spark plug replacement since the engine was installed in 2014. The investigation concluded that the degraded state of the ignition system significantly compromised the engine's ability to produce required power during the approach.
Findings
- The engine's power output was significantly degraded due to worn, corroded, and contaminated spark plugs.
- The magnetos were out of synchronization and improperly timed.
- Improper aircraft maintenance contributed to the engine's inability to meet the power demand during the landing phase.
- The crew's decision-making process contributed to the incident, as the flight was continued despite recurring engine starting difficulties earlier in the flight itinerary.