Has Received Reports Of Uncommanded Engine Shutdowns In Flight

The FAA has issued an AD for Diamond DA42 aircraft following reports of uncommanded engine shutdowns in flight.

According to the FAA, the AD (2017-01-12) was issued as the result of a mandatory continuing airworthiness information (MCAI) issued by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as an uncommanded engine shutdown during flight due to failure of the propeller regulating valve caused by hot exhaust gases escaping from fractured engine exhaust pipes. They have issued the AD to require actions to address the unsafe condition on these products.

Two cases were reported of uncommanded engine in-flight shutdown (IFSD) on DA 42 airplanes. 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 nonremovable 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 Mandatory Service Bulletin (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.

For the reasons described above, this AD is revised to reduce the Applicability, excluding certain post-mod aeroplanes, to allow only installation of the additional brackets as final solution and to remove the prohibition of reinstallation of unmodified exhaust pipes.

(Image from file)

FMI: MCAI