During the post-flight inspection of a Saab 340B passenger
aircraft, the number-two outboard main landing gear wheel was
observed to have sustained noticeable damage. The flight crew
reported that there was no prior indication of the failure, as the
aircraft had handled normally during the landing and taxiing phase
of the flight.
Subsequent examination found that the wheel inner rim had
fractured away from the hub for approximately one-half of the total
circumference. A circumferential fatigue crack had initiated at a
location at the bead seat radius, and had propagated until a final
ductile overload failure caused a section of the wheel rim to
separate.
During the course of the investigation, it was found that the
particular wheel design was being phased out due to recognised
fatigue problems identified at the bead seat area.
Both the manufacturer and operator were aware of the increased
fatigue susceptibility of the earlier wheel design, and had
established increased inspection regimes for those wheels remaining
in service.