The National Transportation Safety Board (NTSB) is urgently recommending that the FAA and Transport Canada require both immediate and more frequent inspections for Bell 407 helicopters. The recommendations are the result of the NTSB’s ongoing investigation into the crash of a Bell 407 that experienced an inflight separation of the tail boom during an on-demand air tour flight near Kalea, Hawaii, last June. Of the six people onboard, the pilot and two passengers were seriously injured and three passengers sustained minor injuries.
“With hundreds currently in service, the Bell 407 helicopter is a popular model among tour operators, police departments, air ambulance providers, and many others, which is why our finding is so urgent,” said NTSB Chair Jennifer Homendy. “We’re calling on regulators to act immediately—before there’s another accident.”
The NTSB’s report (PDF) stated that the upper left tail boom attachment hardware on the accident aircraft was missing although the attachment fitting was still connected to the fuselage. Investigators found the remaining three fittings and hardware still attached to the tail boom, noting that one of the fittings had multiple fatigue fractures and two had overload fractures. Alongside immediate inspections targeting tail boom attachment hardware, the NTSB is recommending that the interval for torque checks of the tail boom attachment hardware and visual inspections of the tail boom attachment fittings be reduced from the currently required 300 hours to “a more conservative number.” The tail boom on the accident aircraft was found to have separated just 114 hours after its last inspection.
Has there been only this one incident that prompts system-wide inspections of every 407’s tail fittings?
Once one goes if they don’t know why it is prudent to check all.
Once one goes if they don’t know why it is prudent to check all.
I am sure that since the helicopter was in the Islands that maybe it was disassembled to get it there? Could that have been the issue?
Inspection interval was 300 hours? This one failed 114 hours after the last inspection? As I understand it, inspection intervals are set such that a latent defect had two chances to be detected before a failure occurs. In this case, it sounds like 50-hour inspections are called or. I don’t know how hard this area is to inspect, but if it’s an easy visual to see “is the bolt/nut really there?” maybe frequent inspections aren’t so bad.
I’m guessing that the “inspection” was pencil whipped.
The inspection’s incudes a torque check.
Typical fasteners materials are a286 steel and Titanium alloys both of these tend to have good fatigue and stress corrosion cracking properties. We do kit have any data of failure mode in these items so an initial drive to increase inspection is a good idea until further details emerge.
As for one failure !? Who knows it may be similar to Alisha air failure where time of flight was nit the crack growth factor but number of airframe cycles. Who knows yet where this investigation finds
.
Honestly, from looking at the NTSB pictures, it looks like ALL the nuts never let go of the bolts. The picture at the top of this article even shows that it was the top-left bolt itself had fractured.
If it’s corrosion or over-torqued bolts, then I don’t think that torque checking the bolts or a visual inspection would find this kind of problem. They should at least do metallurgy on that top-left bolt for what kind of corrosion is on it before concluding that it was simply “loose”.