What happened
On December 10, 2016, a Neiva EMB-201A, registration PT-UAZ, was performing agricultural spraying operations over a cornfield near Erechim, Rio Grande do Sul. The aircraft, operated by Aerodinâmica Aviação AgríSBola Ltda., was applying fungicide when the pilot experienced a sudden and sharp drop in engine oil pressure during the final spray pass.
Unable to return to the origin airport, the pilot executed a forced landing in an unprepared field. The aircraft sustained light damage, but the pilot escaped the incident uninjured.
The investigation
CENIPA investigators examined the engine and the maintenance history of the aircraft. While the aircraft's documentation, including airworthiness certificates and maintenance logs, appeared up to date, investigators discovered that the engine oil leak originated from the failure of the engine crankcase plug.
Technical analysis conducted by the Department of Science and Technology of the Air Force (DCTA) revealed that the propeller governor drive shaft was secured with an improper, non-standard bolt. This bolt had been modified by removing the last threads of its thread pattern to allow for an adaptation. Because this bolt did not meet the manufacturer's specifications, it failed to properly lock the shaft, allowing the drive gear to rotate freely. This movement caused the shaft to strike the engine crankcase plug, wearing down the plug's threads through friction until it detached, leading to the massive oil leak.
Findings
- The engine oil leak was caused by the detachment of the crankcase plug.
- The plug's threads were worn away by mechanical friction with the propeller governor drive shaft.
- The drive shaft was improperly secured using an inadequate, adapted bolt instead of the part specified in the manufacturer's parts catalog.
- The resulting loss of lubrication led to malfunctions in the connecting rods of cylinders 3 and 4, resulting in a loss of engine power.
- Improper aircraft maintenance was the contributing factor to the incident.
Safety action
CENIPA issued a recommendation to the National Civil Aviation Agency (ANAC) to audit the maintenance services provided by the maintenance organization involved (OMAER) to ensure compliance with operational safety and competence standards.