The Transportation Safety Board has issued an air transportation safety advisory ahead of the release of its investigation report into the crash of a ski-equipped Piper J3C-65 Cub on Snowshoe Lake on March 30 of this year.

The accident, which resulted in two fatalities, was caused by the separation of the left main spar wing lift strut assembly near the lower fork end attachment due to excessive corrosion.

In 2015 the U.S. FAA had released an airworthiness directive, AD 2015-08-04, requiring the inspection or replacement of potentially corroded strut assemblies on a number of different Piper models. However, the TSB did not find any evidence that the AD was complied with on the accident aircraft.

During the investigation, the TSB determined that one of the two methods that can be employed to test the wing spar for corrosion, the punch test method, did not return conclusive results when compared with results from an inspection using an electron microscope. This, says the TSB, could lead to an unsafe condition.

In a letter to the director-general of Transport Canada – Civil Aviation (TCCA), contained in the safety advisory, the TSB outlines the results of their tests and recommends that TCCA review the AD with a view to determining effective inspection methods.

The safety advisory can be viewed here.

Photos credit: TSB