Following a number of reports of AW139 helicopters experiencing erroneous crew alerting system messages, the helicopter and avionics system manufacturers established that the design and relative positioning of the external air vent was the source of the problem. Once identified, the helicopter manufacturer issued mandatory service bulletin (SB) 139-166 that was applicable to ‘short nose configuration’ helicopters.
The bulletin provided instructions to identify the presence of corrosion on the Modular Avionics Unit (MAU) modules and also detailed modification of the MAU2 ventilation duct to ensure that the modules were not subject to the direct flow of air from the duct outlet. In addition, following notification of instances of moisture ingress following exposure to heavy rain, the helicopter manufacturer has developed a number of modifications to improve the overall water proofing of AW139 helicopters. Service bulletin 139-105 is currently being prepared to provide the required detail to operators.
The ATSB is satisfied that the action taken by the helicopter manufacturer adequately addresses the safety issue.