What happened
On March 10, 2015, a Robinson R22 helicopter, registration PT-YPB, was conducting a flight instruction mission for a Private Pilot Helicopter (PPH) student near Rio de Janeiro, Brazil. The flight originated from Jacarepaguá Airport (SBJR) for local training maneuvers.
During a 180-degree autorotation training exercise, the crew heard an unusual noise followed by intense vibrations throughout the aircraft. The instructor pilot immediately assumed control of the aircraft and decided to perform a real autorotation to land in a nearby marshy area within the Barra da Tijuca forest. As the pilot performed the flare maneuver near the ground, the tail rotor blades made contact with the water. This impact caused the aircraft to yaw approximately 90 degrees clockwise before touchdown. Both occupants of the aircraft escaped without injury.
The investigation
CENIPA investigators examined the aircraft and found that the tipcap of one tail rotor blade had detached. Analysis by the Department of Aerospace Science and Technology (DCTA) suggested that the loss of the tipcap may have been caused by the degradation of the adhesive due to aging. While the blades had 1,881 hours of operation—below their 2,200-hour life limit—there were no specific maintenance procedures in place for the removal or inspection of the tipcap; maintenance was limited to painting, corrosion control, and crack inspections.
Furthermore, the investigation identified a torsional fracture in the tail rotor drive shaft near the rear transmission box. This fracture was caused by the abrupt deceleration of the tail rotor assembly when the blades struck the water during the landing flare.
Findings
- The loss of the tail rotor blade tipcap caused a dynamic imbalance, resulting in the severe vibrations felt by the crew.
- The torsional failure of the tail rotor drive shaft occurred due to the sudden impact of the tail rotor blades with the water during the landing flare.
- The pilot's execution of the flare at an excessive attitude or low altitude led to the tail rotor blades striking the water.
- The resulting loss of tail rotor effectiveness (LTE) caused the aircraft to rotate clockwise when the pilot increased collective pitch during the final stages of the landing.