What happened
On February 2, 2008, an AS355 F2 helicopter, registration PT-HNH, was performing a flight from Manacapuru to a construction site near Caapiranga, Amazonas. Approximately 20 minutes into the flight, the pilot noticed a decrease in Ng (gas generator speed) and an increase in temperature in engine number two. No fire warnings were initially triggered on the cockpit alarm panel.
In response to the engine malfunction, the pilot executed an emergency landing on a dirt road. Following the touchdown, the pilot discovered that engine two was on fire. The pilot attempted to use the onboard fire extinguisher, but it failed to function. The crew and passengers eventually used mud from the landing site to help suppress the flames until personnel from a nearby construction site arrived with chemical powder extinguishers to extinguish the fire.
The investigation
CENIPA investigators examined the aircraft and the maintenance history of the operator. While the pilot and passengers were uninjured, the aircraft sustained substantial damage to the engines, transmission, and rotors.
Testing of the alarm panel after the incident showed that the panel itself was functional; however, the fire detection system could not be fully verified because the detectors and wiring had been destroyed by the fire. Investigators found that the maintenance crew had been routinely de-energizing the fire detection system via the Circuit Breaker to avoid frequent false alarms caused by high humidity at the operational base.
Technical analysis of the engine by Rolls-Royce revealed that a fuel line connection at the fuel pump output had been torqued below the manufacturer's specified limits. Furthermore, investigators discovered an unauthorized "jumping" (unapproved bypass) in the electrical panel's integrated circuit, which posed a significant risk to the aircraft's electrical system.
Findings
- Improper maintenance practices: The mechanic performed maintenance tasks based solely on experience rather than consulting the required manufacturer manuals or troubleshooting guides.
- Inadequate supervision: The company's maintenance management failed to provide adequate oversight for corrective maintenance performed at remote operational sites.
- Substandard tooling: The maintenance kit used at the site lacked control and included precision tools that had not been verified for calibration.
- Operational deficiencies: The company operated from a base not listed in its approved Operational Specifications and lacked proper controls for daily fuel sampling and quality testing.
- Incomplete documentation: The maintenance crew lacked access to the General Maintenance Manual (MGM) and technical catalogs at the operational site.