What happened
On March 15, 2007, a Socata TB 9, registration F-GCEZ, was conducting a solo navigation flight from Agen to the Tarbes Lourdes Pyrénées aerodrome. During the approach to runway 20, the student pilot detected a burning odor inside the cockpit. In response to the potential hazard, the pilot initiated a go-around and decided to perform an emergency landing on the available runway. The pilot requested that airport fire services be placed on alert prior to touchdown. The aircraft landed without further incident or damage to the airframe.
The investigation
Post-flight inspections of the engine compartment revealed burn marks and a hole on the engine cowling. Investigators examined the exhaust system and identified that an exhaust pipe had become detached at a clamp location. The inspection of the clamps showed that the clamp ears were deformed and touching one another. /nFurther investigation into the maintenance history revealed that the clamps and associated hardware had been replaced in January 2006. During that maintenance event, the mechanic observed an existing installation using a nut and locknut and subsequently used the Illustrated Parts Catalog (IPC) to replicate that specific configuration. The parts used for the installation were sourced from the workshop's existing stock.
Findings
- The primary cause of the incident was a non-compliant maintenance procedure regarding the exhaust system installation.
- The maintenance performed in 2006 failed to adhere to mandatory Service Bulletin (SB) 10-072-78, which requires specific flange hardware and the use of self-locking nuts.
- The technician relied on an incorrect page of the IPC that did not account for the modifications required by the mandatory SB.
- The installation involved excessive tightening of the clamps, causing the ears to deform and touch, which is explicitly identified as an unacceptable condition in the service bulletin.
- The hardware used for the installation was not in accordance with the updated safety requirements for the TB 9 fleet.