What happened
On May 26, 2016, a Neiva EMB-711C, registration PT-NMT, was performing a private flight from Divinópolis to Goianá, Minas Gerais. The flight had previously diverted to Divinópolis due to poor weather conditions at the destination. Upon attempting the flight again once visibility improved, the aircraft began its descent toward the destination airfield.
At approximately 4,000 feet, the pilot heard a metallic grinding noise, followed immediately by a drop in oil pressure to zero and the activation of the oil pressure warning light. The engine failed completely. The pilot declared an emergency and, unable to reach the runway, performed an emergency landing in a field of low vegetation near a stream, approximately 2.8 NM from the airfield. The aircraft sustained substantial damage, while the pilot sustained minor injuries.
The investigation
CENIPA investigators and technical experts from DCTA conducted a detailed examination of the engine. The investigation focused on the lubrication system and the mechanical integrity of the engine components. The analysis revealed that the engine's lubrication was restricted at the drive shaft of the vacuum pump.
Technicians discovered that a burr on the adapter gasket had not been removed during a previous maintenance procedure. This obstruction partially blocked the oil flow to the drive pinion. This lack of lubrication caused increased friction and heat, leading to the thermal expansion of the shaft and a subsequent crack in the vacuum pump adapter. This mechanical failure caused an overload that sheared the dowel pin responsible for timing the engine's gears, resulting in the total loss of engine synchronization and the subsequent engine shutdown.
Additionally, the investigation found significant inconsistencies in the aircraft's maintenance records. While the aircraft's airworthiness certificate was valid, the total flight hours recorded in the logbooks did not align with the entries in the aircraft's primary log, compromising the reliability of the maintenance data.
Findings
- Maintenance oversight: A burr left on a gasket during maintenance caused restricted oil flow to the vacuum pump drive shaft.
- Mechanical failure: The resulting overheating and expansion led to a cracked adapter and the shearing of a critical dowel pin, causing engine desynchronization.
- Record-keeping discrepancies: Inconsistencies were found between the aircraft's total time logs and the maintenance history records.
Safety action
CENIPA issued recommendations to the National Civil Aviation Agency (ANAC) to:
- Ensure the maintenance organization inspects all components thoroughly before installation, specifically focusing on removing burrs from gaskets.
- Verify that the maintenance organization possesses and applies all necessary resources and technical manuals required for Embraer EMB-711C services.
- Ensure the operator improves administrative oversight of maintenance records and flight hour tracking.