What happened
On January 26, 2007, a Commander 112, registration PT-JPZ, was performing a flight from Penápolis, SP, to Arapongas, PR. While cruising at 6,500 feet, the pilot heard a loud bang followed by intense vibration and a sudden loss of engine power.
As the pilot attempted to divert to the Londrina Airport, the engine failure was accompanied by the appearance of fire. Due to the critical situation, the pilot was forced to execute an emergency landing on an avenue in the northern sector of Londuna. During the final approach, the aircraft's right wing struck electrical power lines. After contacting the pavement, the aircraft struck a wall and slid until coming to a complete stop. The aircraft was destroyed by a post-impact fire.
The investigation
CENIPA investigators examined the engine components and found significant internal damage, including cracks, missing block parts, damaged connecting rods, and a damaged crankshaft. Analysis of the crankshaft revealed signs of overheating and heavy friction.
Technical inspections of the maintenance records showed that the aircraft had undergone a 100-hour inspection only 36 minutes prior to the accident. The investigation focused on the assembly of the crankshaft counterweights. According to the manufacturer's Service Instruction (SI nº. 1012F), the counterweights must be installed using four pins, paired specifically by part number. However, the investigation established that the maintenance was performed incorrectly, with only two pins installed.
Findings
- Improper engine maintenance was the primary cause, as the incorrect installation of the crankshaft counterweight pins created imbalance and vibration.
- This vibration caused the third main bearing to displace, which blocked the oil lubrication path and led to the engine failure.
- Inadequate maintenance supervision allowed the non-compliance with technical publications to go undetected during the engine overhaul.
- The pilot sustained severe injuries, including second-degree burns over 25% of his body, but was able to evacuate the burning aircraft.
Safety action
Following the investigation, safety recommendations were issued to alert maintenance inspectors and mechanics regarding the necessity of strictly consulting technical publications. Additionally, maintenance companies servicing Textron Lycoming engines were advised on the critical importance of supervising services to ensure counterweight assembly complies with established Service Instructions.