Spanish and US investigators have clashed over the origin of a metallic fragment blamed for a tyre-burst on take-off, substantially damaging a Delta Air Lines Boeing 767-300ER.
While a Spanish inquiry has concluded that the fragment was left inside the tyre during retreading, US counterparts believe it was already present on the runway at Madrid Barajas, from where the 767 departed for New York JFK.
As the aircraft (N182DN) accelerated the right-hand aft tyre on the right main landing-gear burst, and debris punctured the underside of the wing, damaging 13 hydraulic lines and causing components to detach. These punched through the upper wing surface, resulting in the loss of a panel.
Damage to the hydraulics meant the undercarriage could not be retracted and the crew of the 767 opted to return to Madrid.
It landed on runway 32L at 169kt but, owing to the loss of the centre and right hydraulic systems, as well as nose-wheel steering, the aircraft could only be slowed and steered using limited functions. These included the left-hand reverse thrust, three of the 12 spoilers, the rudder, and the accumulator system.
Rudder steering authority was lost below 80kt and the 767 veered to the left, its accumulator fluid exhausted, and exited via the last taxiway before rolling to a halt on a grassy area 10,500ft past the threshold and 600ft from the centreline.
At the centre of the probe is a stainless steel fragment 87mm long which was found on the departure runway 36L.
Spanish investigation authority CIAIAC says the tyres on the right main gear had been retreaded by Goodyear in Arizona in July 2013, and had undertaken 145 cycles before the 5 December 2013 event.
The inquiry refers to problems obtaining specific data on the retreading process, owing to intellectual property laws – CIAIAC mentions having sent formal protests over the matter.
CIAIAC acknowledges that introduction of the fragment during retread would have been “difficult”, given the inspections carried out as part of the process. But it also finds tyre penetration by the thin fragment “unlikely”, and points out that the debris was discovered immediately by a team which had inspected the runway 15min earlier with no findings.
The Spanish inquiry believes the fragment “remained inside” the tyre during the retread, and has recommended that Goodyear reviews its quality control.
US National Transportation Safety Board investigators, however, have disagreed with this conclusion, stating that it is not supported by factual information.
Its analysis found no evidence of problems during the retread process, and shearography images indicated “no evidence” of foreign objects in the tyre or errors in quality control.
The metal fragment had no rubber debris attached but showed scratches and corrosion consistent with having been present on the runway for a “considerable time”, it states. While it accepts that the runway was inspected before the incident, it says there are no details on how this was conducted.
NTSB analysts believe the tyre burst was “likely” to have resulted from a high-speed impact with a foreign object during take-off. It has not indicated whether this object was the metal fragment or a different piece of debris.
Goodyear has also submitted detailed comments to CIAIAC, casting doubt on the inquiry’s findings, claiming that it “fails to account” for available information on the appearance of the tyre involved.
Source: Cirium Dashboard