Fatal Accident Prompts Airwolf Solution to Enstrom Spindle Problem
Resource from: Aviation International News Likes:240
Mar 05,2015
Airwolf Aerospace of Middlefield, Ohio is developing tension torsion (TT) straps for all piston-powered Enstrom Helicopter models to replace the existing Lamiflex bearings currently used. This will eliminate the possibility of spindle thread failure as outlined in FAA Emergency Airworthiness Directive (EAD) 2015-04-51.
According to the FAA, “This EAD was prompted by a fatal accident. The investigation is ongoing, however, preliminary results indicate that the accident was caused by a crack in the spindle, which resulted in the main rotor blade separating from the helicopter. The crack was discovered at the last thread of the spindle retention nut threads. While the investigation could not determine when the crack initiated, it was able to determine that the crack existed, undetected, for a significant amount of time before the separation.”
Replacing the Lamiflex bearings with TT straps eliminates the spindle threads. According to Airwolf, TT straps are known to be “vastly superior to Lamiflex bearings, as they are far smoother in flight and do not degrade and cause the rotor system to go out of balance. In addition, they make track and balancing of the blades far simpler.”
Airwolf expects the price for the components of the complete modification kit will be less than $12,000. Because of the lower blade loads found on Enstrom’s piston helicopters compared with its turbine Model 480, Airwolf anticipates that the TT straps will have a service life of 60 months/1,200 hours, which is the same as the antiquated Lamiflex bearings.
Meanwhile, Airwolf has been working with Enstrom to develop and supply 36-month/1,200-hour-life TT straps for Enstom 480s. FAA certification of these straps is expected soon. Their life limit is said to be 50-percent longer than the TT straps currently available for the 480.
Airwolf also offers straps for the Bell 206 JetRanger, LongRanger, OH-58, 204, 205, 212 and UH-1.
(Aviation International News)
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