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The European Aviation Safety Agency (EASA) has followed Leonardo in calling for modification of the way Leonardo AW189 underbelly fuel tank systems for extended range are bonded to the helicopter, after highlighting a possible explosion risk in the current system.
In a proposed airworthiness directive (17-096), EASA said the safety issue was related to the electrical bonding installed on the fuel sump plate, which was identified during a review of the underbelly fuel tank system.
The underbelly tank fuels sumps and the fuel sump covers are bonded to the external helicopter skin in the same location, and in case of a lightning strike, a fraction of the electrical current could be diverted inside the sump plate and into the electrical wiring connected to the components inside the fuel tanks, the regulator said.
“This condition, if not corrected, could, under certain conditions, create an ignition source in the fuel tank vapor space, possible resulting in a fuel tank fire or explosion,” the proposed airworthiness directive (AD) states.
As a counter measure, the AD would require operators to modify the electrical bonding of the underbelly fuel tank sumps by replacing and re-routing the existing copper straps with bonding cables, in accordance with an alert service bulletin (189-100) issued by Leonardo Helicopters on July 13, and within 300 hours of the effective date of the AD.
The proposed AD will be closed for consultation on July 31, 2017.
UPDATE: Leonardo provided the following statement to Vertical:
“With safety as its first priority, Leonardo notified EASA of the potential issue as soon as it became aware of it. The issue was identified in the framework of the usual internal quality and airworthiness review process carried out by Leonardo, not by the airworthiness authorities, operators or as a result of occurrences. The company immediately released a rectification service bulletin accordingly (which the EASA Proposed Airworthiness Directive refers to) for the nine aircraft in the fleet fitted with the underbelly fuel tank.
“It is also worth noticing the 300 flight hours compliance was set in coordination with EASA and indicates a low risk case.”