A local Defence/industry team has come up with an innovative solution to a problem which, until now, has affected the serviceability of the air to air refuelling (AAR) hoses fitted to the RAAF’s Airbus KC-30A multi-role tanker transport (MRTT) fleet.
The solution, developed by No.33 Squadron at Amberley in partnership with Northrop Grumman Australia and the Defence Aviation Safety Authority (DASA), uses non-destructive inspection (NDI) Eddy Current Array (ECA) technology to detect corrosion in the hoses and has now been mandated for use by the original equipment manufacturers, Airbus Defence and Space and Cobham.
The problem affects the hoses installed in Cobham’s 905E refuelling pod, one of which is installed under each wing of the RAAF’s KC-30As and similar aircraft operated by the international MRTT community. A similar pod is also used by the Airbus A400M transport/tanker and the issue affects aircraft from several nations around the world.
In 2016 an RAAF KC-30A suffered an incident, losing the basket and MA-4 coupling from an AAR hose assembly inflight and subsequent investigation determined that the failure was caused by corrosion of the steel braiding used to form the core of the hose. In response, the OEM issued an Airworthiness Directive (AD) which mandated an external visual inspection of the 90ft hose after every pod operation - a procedure which requires up to five people to manually deploy. However, the braided hose in encased within a neoprene shroud and many defects can potentially remain undetected by visual inspection alone.
“The steel braid core bears the load on the hose when it is extended and that’s where the failure occurs,” explains 33 Squadron’s Senior Engineering Officer, Squadron Leader Simon Chittleborough. “Northrop Grumman Australia looked at the problem and worked with DASA’s Non-destructive testing and composite technology section to look at how we could do this better, because we realised that we weren’t really addressing the risk and there was a better way of inspecting the hoses.”
The solution uses a special annular eddy current probe, developed in conjunction with Canadian ECA NDI specialist company EddyFi, which clasps around the hose and permits a 360-degree detailed inspection of the hose to be accomplished either on wing or in the workshop. The inspection takes only one minute or so to complete once the hose is extended and the system indexed, and the entire procedure can be accomplished in around one hour.
“From an availability perspective, the procedure allows us to monitor the propagation of corrosion with millimetre accuracy, so we can monitor it closely and allow the hose to remain in service longer, until the limit is reached,” SQNLDR Chittleborough says. “That also decreases cost; we go through 10-15 hoses every year, even during normal operation, most hoses are replaced due to general wear and tear but now we can determine whether corrosion is the driving factor for replacement.”
Corrosion has been detected even in new hoses supplied by the manufacturer and the new procedure allows the operator to determine whether the hose is serviceable before it is installed in the pod in the first instance.
“We fed that information back to the manufacturer to help improve the manufacturing processes and procedures, which has subsequently led to the new product we now receive from the factory being free of defects,” adds Northrop Grumman Australia’s AAR technical support engineer, Stratos Patsikatheodorou.
While the visual inspection requirement will also remain in place for the foreseeable future, Cobham is understood to be developing a new hose, which is likely to become available next year.