What happened
On September 13, 2001, an EMB 711C, registration PT-NEE, departed Campo Mourão (SSKM) for a local test flight following an annual maintenance inspection (IAM). During the departure from the traffic pattern, the aircraft experienced a propeller overspeed (disparo de hélice). The pilot immediately retarded the propeller and power levers to mitigate the effects and attempted to return to the runway. However, at approximately 1,500 feet, the engine ceased functioning. The pilot performed an emergency landing in a plowed field approximately 15 km northeast of the airfield. The pilot escaped the aircraft uninjured, though the aircraft sustained severe damage to the engine, propeller, landing gear, and fuselage.
The investigation
CENIPA investigators examined the aircraft and the maintenance history performed by the maintenance facility. The investigation focused on the engine's lubrication system following the discovery of significant oil leakage along the underside of the fuselage. Investigators found that the engine oil dipstick was clean, yet oil was present throughout the forward and rear sections of the fuselage.
Upon inspection of the engine, investigators identified the absence of the oil pan drain plug (bujão do cárter). A piece of safety wire (freno) was found at the plug's attachment point, with evidence that the wire had been cut with pliers. The investigation established that during the recent maintenance inspection, the oil pan had been drained to clean the lubrication system components. It was determined that the safety wire was likely not replaced or properly secured after the oil was replenished, allowing the plug to gradually unscrew due to engine vibrations during ground testing and flight.
Findings
- Inadequate maintenance: The oil pan drain plug was missing, which led to a total loss of engine oil.
- Maintenance supervision failure: The aircraft was released for a test flight without detecting that the safety wire was missing or that the plug was improperly secured.
- Mechanical sequence: The loss of oil caused a drop in pressure within the propeller governor, triggering the propeller overspeed, followed by total engine failure due to lack of lubrication.