Failure analysis of suspension device fitted with antenna of a helicopter

A failed suspension device fitted with the antenna of a helicopter was forwarded to this laboratory for investigation. Following this, another suspension device fitted on to the same aircraft which broke post installation onboard, was also forwarded for failure analysis. Examination revealed that both the devices broke in a similar fashion wherein rotary bearing assembly got separated from the base plate and along the weld joint. Study of the fractured regions did not show any evidences of progressive failure such as fatigue and/or stress corrosion cracking. Instead, gross deformation in the base plate preceded the separation of the rotary bearing assembly. All the fastener holes on the base plate were also found deformed and elongated. These indicate that the failure of the suspension device was due to sudden inadvertent load on the component while in operation. Considering the mode of failure and the identical nature of failure in both the cases, it appears most probable that the failure was due to some problems related to functioning of the antenna deployment/retraction system installed in this particular aircraft