What happened
On August 16, 2014, an S-61N helicopter, registration PR-HRV, was performing a passenger transport flight from Porto Urucu to Porto Hélio, Amazonas, carrying two pilots and eleven passengers. During the final approach to a clearing, the crew detected an abnormal noise and a significant loss of power in the right engine, noting a drop in torque and an increase in temperature above limits.
The commander immediately executed a go-around to stabilize the aircraft. Following established emergency procedures, the crew shut down the right engine and transitioned to single-engine operations. The aircraft returned to Porto U/rucu, where the pilot performed a successful landing on runway 27 without further incident. All 13 occupants (two crew and eleven passengers) were unharmed, though the aircraft sustained minor damage.
The investigation
CENIPA investigators examined the right engine, which was sent to Vector Aerospace in Canada for analysis. The examination revealed extensive damage to all ten stages of the rotary compressor and the power turbine blades. The investigation established that the engine failure was caused by Foreign Object Damage (FOD) resulting from the ingestion of a fastener.
Laboratory analysis of the remaining portion of the air intake screen's rod clamp screw, conducted by the Department of Science and Technology (DCTA), utilized stereoscopic and electron microscopy. These tests revealed that the screw had failed due to fatigue caused by alternating bending stress. This failure occurred approximately 40 flight hours after the air intake screen had been reinstalled during a 150-hour inspection.
Findings
- The engine failure was caused by the ingestion of a foreign object (a fastener).
- The fastener failed due to fatigue from alternating bending stress.
- The fatigue was likely caused by improper installation (rigging) of the air intake screen rod clamp, potentially involving incorrect torque, improper locking, or inadequate inspection.
- The aircraft was within weight and balance limits, and the crew was properly qualified and experienced.