A Senate inquiry into a fatal helicopter crash that claimed the lives of four servicemen has been “hampered” by highly technical questions returned by Defence officials just days before the hearing. An investigation by the Defence Flight Safety Bureau ultimately concluded spatial disorientation was the primary cause of the crash by Captain Lyon and his co-pilot, Lieutenant Nugent. Major General Hefner said a new safety summit had been established with international partners and fatigue management procedures had been probed. Questioned whether he regretted using TopOwl, he noted that the Defence Flight Safety Bureau report found it was “very unlikely” that the helmet mounted sighting device contributed to spatial disorientation. The crash led to the entire Taipan fleet being retired early,Major General Hefner said he would have to take on notice what happened to remaining Taipan airframes.