In East Timor in 2001 during a daily inspection, a large crack was found in the root of one of the main rotor blades of one of the Iroquois helicopters. DTA investigations showed that the crack was caused by the progressive delamination of a metal reinforcement pad and, with the change in load distribution leading to fatigue cracking of the underlying structure, the main rotor blade was nearing fracture.
As existing non-destructive inspection techniques were not able to detect the delamination, DTA developed a new strain-based non-standard inspection procedure and set pragmatic service limits.
Since the introduction of these measures, all defective main-rotor blades have been withdrawn from service before any delamination has begun to grow rapidly or dangerously and any cracking by the same mechanism was prevented.
This effective monitoring enabled the RNZAF to maintain the airworthiness of its Iroquois fleet.