European Aviation Safety Agency

ATA 78 - Engine Exhaust - Exhaust Pipes - Replacement
 N AD 2016-0156R1

Annotation

Reason:

Two cases were reported of uncommanded engine in-flight shutdown (IFSD) on DA 42 aeroplanes. Subsequent investigations identified these occurrences were due to failure of the propeller regulating valve, caused by hot exhaust gases coming from fractured engine exhaust pipes. The initiating cracks on the exhaust pipes were not detected during previous inspections, since those exhaust pipes are equipped with non-removable heat shields that do not allow inspection for certain sections of the exhaust pipe.

This condition, if not corrected, could lead to further cases of IFSD or overheat damage, possibly resulting in a forced landing, with consequent damage to the aeroplane and injury to occupants.

To address this potential unsafe condition, Diamond Aircraft Industries (DAI) developed an exhaust pipe without a directly attached integral heat shield that allows visual inspection over the entire exhaust pipe length. DAI issued MSB 42-120 and relevant Working Instruction (WI) WI-MSB 42-120, providing instructions to install the modified exhaust pipes. As an interim measure, an additional bracket was designed to hold the exhaust pipe in place in case of a pipe fracture.

Consequently, EASA issued AD 2016-0156, requiring replacement of the exhaust pipes with pipes having new design, and prohibiting (re)installation of the previous design pipes.

Since that AD was issued, cracks were identified on modified exhaust pipes during an inspection. Furthermore, it was determined that the additional brackets provide a level of safety equivalent to the modified exhaust pipes. Consequently, DAI revised MSB 42-120, allowing installation of the additional brackets as alternative to the installation of the modified exhaust pipes.