What happened
On August 30, 2004, an Agusta A-119 helicopter, registration PR-HVR, was performing a demonstration flight for a potential client at the Málaga Helipad in Osasco, São Paulo. The flight was intended to showcase the aircraft's capabilities. During the takeoff phase, shortly after leaving the landing area, the aircraft experienced a loss of main rotor RPM, accompanied by a red warning light and an audible alarm.
The pilot attempted to recover the rotor speed by adjusting the collective lever, which provided only momentary stabilization before the RPM dropped again. Faced with the inability to maintain sufficient rotor speed, the pilot executed a forced landing on the pavement of a nearby factory yard. Upon impact, the aircraft's residual power caused it to rotate 180 degrees and slide approximately 15 meters down a slope, eventually coming to rest against a metal fence. The pilot sustained minor injuries, while the five passengers remained uninjured.
The investigation
CENIPA investigators examined the aircraft's maintenance history and the engine's performance. The engine, a Pratt & Whitney PT6B-37A, had been subjected to testing at the manufacturer's facilities. These tests successfully reproduced the malfunction reported by the pilot during the accident.
While investigators noted that some maintenance fasteners were incorrectly installed during a previous service, they determined this did not contribute to the accident. The investigation focused on the Electronic Governor Unit (EGU), which transmits information to the Fuel Control Unit (FCU). Analysis revealed that the engine's stability was compromised by an extreme sensitivity to internal parameter variations.
Findings
- The primary cause of the accident was a malfunction of the engine's fuel control system.
- The instability was driven by a material factor: the extreme sensitivity of the control system to intrinsic operational variations, where a minute change in the EGU output was sufficient to render the engine unstable.
- The investigation identified a chronic manufacturing or design deficiency in the engine's fuel control components, a known issue that had prompted numerous Service Bulletins from Pratt & Whitney Canada prior to the event.
- Human and operational factors did not contribute to the occurrence.