Undetected fatigue cracking results in wheel rim fracture

Undetected fatigue cracking results in wheel rim facture

Key points:

  • Wheel rim fractured and tyre deflated due to undetected fatigue cracking, a known issue
  • Non-detection likely due to inadequate guidance on inspection requirements for wheels operated with a flat tyre

A Saab 340 main landing gear wheel rim fracture and tyre deflation was likely due to insufficient guidance in the operator’s maintenance procedures for component maintenance inspections, a new ATSB reports says.

On 20 August 2019, a Regional Express Saab 340B, registered VH-ZLX, departed Adelaide, for a scheduled passenger flight to Port Lincoln. During the post flight walk around after landing, the first officer discovered that the left main outboard landing gear tyre was deflated and that a piece of the wheel was missing. The missing section of the wheel was recovered from the runway strip at Adelaide.

The wheel had been fitted to VH-ZLX on the day of the incident, after its removal from another aircraft in July 2019, due to the detection of an audible leak. It was returned to the operator’s maintenance facility with an ‘unserviceable’ tag and ‘repair’ noted on the standard tyre change form. The operation of the wheel with a deflated tyre was not noted.

ATSB examination of the wheel found an area of fatigue cracking had developed in the bead seat region and progressed 86 mm around the circumference before the rim section separated due to overstress, a known issue with this wheel type previously resolved with updated maintenance schedules and practices.

The large size of the fatigue area along with the relatively low number of flight cycles since its last non-destructive testing indicate the cracking could have been detected following its removal in July 2019.

The ATSB determined that the opportunity to detect the fatigue cracking was limited as the operator’s wheel maintenance forms did not adequately convey the inspection requirements for wheels operated with flat tyres. As a result, inspections that may have detected the crack were not carried out.

The ATSB safety message from this investigation highlights that when situations or issues arise that do not fit into standard operating procedures, maintenance personnel should always be prepared to consult or request further guidance. This guidance can come from internal support materials, such as procedures, or external materials such as maintenance manuals or the manufacturer.

In response to the incident, Regional Express have updated their wheel maintenance procedures to ensure that non-normal inspections are identified and carried out. The airline has also reinforced to maintenance personnel the need to fully complete unserviceable tags to ensure subsequent maintenance personnel fully understand the nature of reported defects.

You can find here the investigation report AO-2019-047: Landing gear wheel failure involving a Saab 340, VH-ZLX, Adelaide Airport, South Australia on 20 August 2019

/Public Release. View in full here.