What happened
On January 19, 2011, an EMB 721D aircraft, registration PT-RHW, was performing a passenger transport flight from Manoel Urbano, AC, to Eirunepé, AM. Approximately 15 minutes before reaching its destination, the pilot noticed a loss of engine power. Following the failure, an oil leak began emanating from the engine cowling, eventually reaching the windshield.
In response to the emergency, the pilot identified a suitable landing site on a beach along the Tarauacá River, measuring approximately 50 meters wide and 1,500 meters long. To mitigate the risk of fire, the pilot shut down all electrical equipment and performed the landing with the landing gear retracted. The aircraft struck the ground at an approximately 10-degree pitch, sliding 100 meters before the right wing struck a sandbar, causing the aircraft to rotate 90 degrees. All four occupants (the pilot and three passengers) escaped the crash uninjured, though the aircraft sustained severe damage to the engine, propeller, left wing tip, left elevator, and flaps.
The investigation
CENIPA investigators examined the engine components through laboratory analysis at the Department of Science and Technology (DCTA). The investigation focused on the maintenance history of the Lycoming engine, specifically regarding the installation and machining of dynamic counterweight bushings.
Technical examinations revealed that a component—the Part Number 71907 Washer Dynamic Counterweight—had failed due to fatigue. The investigation found that during a previous engine overhaul, the maintenance facility had outsourced the machining of the bushings. This outsourced service failed to follow mandatory manufacturer instructions, specifically Service Bulletin 204V-2 and Service Instruction Nr 1143B, which require a specialized eccentric rectification process to ensure the bushings are correctly centered.
Findings
- Improper maintenance procedures during the engine overhaul led to the wear of the dynamic counterweight bushing.
- The maintenance workshop failed to adhere to mandatory Service Bulletin 204V-2 and Service Instruction Nr 1143B.
- The outsourced machining service did not provide the required documentation (form SEGVOO 003) to prove compliance with regulatory standards.
- The fatigue failure of the bushing caused the engine power loss and subsequent oil leak.