Fractured Exhaust Pipes Led To Uncommanded Engine Shutdowns In Two Cases

The FAA has issued an Airworthiness Directive (AD) for Diamond Aircraft Industries GmbH Model DA 42 airplanes following a similar MCAI action by EASA.

According to the AD (2017-11-08), two cases have been reported of uncommanded engine in-flight shutdown (IFSD) on DA 42 airplanes. Subsequent investigations identified that 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. EASA issued AD 2016-0156 (later revised), requiring replacement of the exhaust pipes with pipes having the new design, or installation of the additional brackets.

Since EASA AD 2016-0156R1 was issued, cracks were found during inspection on modified exhaust pipes. Further investigation determined that, with the modified exhaust pipe design, vibration leads to cracking.

To address this potential unsafe condition, DAI published MSB 42-129 providing instructions for inspection of modified exhaust pipes.

The MCAI allows for either replacement or repair if a cracked exhaust pipe is found during an inspection. This AD will only allow for replacement. If there were to become a parts availability issue at some time, we would consider the welding repair as an alternative method of compliance.

(Image from file)

FMI: AD