Suspicion that the crash of a Bell 407 in the Gulf of Mexico was caused by a tailrotor strike has prompted Canadian and US airworthiness authorities to re-impose a speed restriction on the light helicopter. Some 485 Model 407s are in service worldwide.
An emergency airworthiness directive (AD) reducing never-exceed speed (VNE) from 140kt (260km/h) to 110kt as a "precautionary measure" has been issued, although the cause of the 29 December crash of a Petroleum Helicopters International (PHI) aircraft has yet to be determined. The AD says the helicopter was flying at around 260km/h when it hit the water after an "in-flight occurrence", killing the lone pilot.
Part of the tailboom has been recovered, but not the aft section with the tailrotor, gearbox and vertical fin. Although sources say there is no firm evidence that the tailrotor hit the tailboom, it is this aft section that separated in three previous accidents involving tailstrikes on the Bell 407.
In March 1999, after the third accident, Canadian and US airworthiness authorities issued an AD requiring installation of a tailrotor pitch-limiting left-pedal stop and restricting VNE to 100kt. Bell then redesigned the tailrotor, developing an airspeed-actuated pedal stop, installation of which allows the 407's VNE to be restored to 140kt.
Although the AD mandating installation of the redesigned tailrotor, modification of the vertical fin and horizontal stabiliser and installation of the electronic pitch stop does not take effect until 31 January, the PHI crash aircraft was already fully modified.
Source: Flight International
