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Old 10th Oct 2018, 17:49
  #13 (permalink)  
ShyTorque

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 12,289
At some stage the Puma maintenance manuals regarding the tail rotor control cables were changed from "lifed" to "on condition". Unfortunately, the manuals weren't changed to include a check on the condition of said cables...

One of our aircraft (230 Sqn) suffered a tail rotor drive shaft failure caused by a loose intermediate gearbox (Hameln, Germany, early 1980s). That was caused by the gearbox attachment bolts not having enough thread cut on them so the torque checks just tightened the nuts at the shank end of their threads, rather than securing the gearbox!

During the investigations for that (fleet check) a significant number of Pumas were found to have badly frayed tail rotor cables as they ran over a pulley and nylon guides at the lower end of the tail pylon. It was then I began asking questions about the consequences of a broken tail rotor control cable. No-one seemed to be able to answer, or too interested in finding out. After some investigation I realised that if this occurred, the tail rotor pitch would run away to either full positive, or full negative pitch because there was nothing to oppose it, i.e. to centralise the servo valve.

In the mid 1980s I gained access to civilian Super Puma manuals and discovered they had a tail rotor servo valve centreing device fitted, RAF ones didn't, despite it apparently being a simple bolt-on mod. I pushed a letter explaining this to the appropriate Puma upper management in the mid 80s. I moved away from rotary but returned in the 1990s and nothing had been done about it even then, nor was it done when I left the service a few years later. I have no idea if the HC2 has been modified in this respect and one crew I asked (including a QHI) didn't seem to know either.
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