Tread Separation causing Tire Failure
During cruise and approximately 4 hours prior to landing at the scheduled destination, the crew reported low hydraulic quantity in the center hydraulic system. An emergency was declared prior to landing and the aeroplane was met by emergency vehicles on arrival. The crew performed an uneventful landing, shut the engines down on the runway and was towed to the gate due to the inoperative steering system from the loss of the center hydraulics. Maintenance inspection at the gate confirmed extensive tire damage including the under-wing area and flap panel along with the associated tires brake line, which was the source of the hydraulic fluid loss.
Through further analysis and the retrieval of tire debris from the departing airport, it was concluded that the tire failed on take-off, damaging the aeroplane and causing the eventual loss of the hydraulic system. Concerns were raised of possible foreign object damage (FOD) being picked-up off the runway, causing the tire failure, but no direct evidence to support this was found.
The tire was replaced and sent to Bridgestone where a complete shop inspection and analysis was performed where no conclusive findings or indication of its failure or FOD was found. With this particular tire, an initial retread was applied where there were no clear indications of low adhesion between the tire retread components. The tire had also completed 139 landings prior to its failure and typically flaws with material or workmanship during the retreading process would result in a tread separation quickly after installation.
The concluding corrective action defined by Bridgestone is the standard tire maintenance practice of the operator which includes checking for indications of damage from FOD or any signs of developing bulges of bubbles. Maintaining correct tire pressure inflation are also essential preventative measures to help guard against the possibility of tread separation, tire failure and possible extensive aircraft damage.
||Tire tread separation failure and hydraulic leakage|
CAWIS Airworthiness Directive Listing for Aerospatiale Model AS 355N and AS 355NP Rotorcraft
A client has recently brought to our attention that several (18) Airworthiness Directives (AD) issued by the Directorate General for Civil Aviation of France (DGAC) were not associated with the Aerospatiale AS 355N as would be expected. These ADs are “mature” and were issued between 1981 and 1987. The cause of this error has been traced to an administrative error.
A review of these ADs would indicate they should be associated to the AS 355N/NP model helicopters. As such the following ADs have now been associated in CAWIS with the AS 355N and NP helicopters.
Owners and operators may wish to review their records to insure these ADs have been correctly dispositioned. As with any AD, there may be situations where it does not apply to a particular serial number.
Transport Canada Civil Aviation thanks the client and request any discrepancy with the AD database be reported to CAWwebfeedback@tc.gc.ca.
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