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The lubricating oil supply to the RGB comes from the engine’s oil pressure pump that is driven by the compressor section – the other shaft in the engine: N1, not N2. See the problem? When the propeller is allowed to turn without the engine running, no lubrication is supplied to the gears and bearings in the RGB except for residual oil that was originally there.
So that is why airplanes with PT6 engines are always supplied with some type of propeller restraint device that can be connected to the propeller when parked on a windy ramp: The engine people want to prevent propeller and RGB and N2 shaft rotation when no positive lubrication is being supplied. Beech’s factory-provided restraints consist of a rubberized fabric sleeve that fits over the end of one propeller blade and two elastic straps that connect the sleeve to two rubberized fabric exhaust stack covers.
Questions have often been raised during initial and recurrent King Air pilot training classes about the importance of and use of the restraints. A common one is “How important is it to stop rotation? If I am just going to be in the FBO for 15 minutes, paying the ramp fee, should I put the restraints on?” Also, “How cool should the exhaust stacks be before I attach the restraint?” And the ever-popular “Should I place the propeller blade with the sleeve attached in the up or down position?”
There are not black-and-white, right-or-wrong answers to these questions. Some operators let the props spin for an hour or more while others install the restraint immediately before leaving the airplane alone. Some exhaust stack covers are more heat-resistant than others, and some pilot’s fingers are more heat sensitive than others! The up versus down question? I doubt that one will ever be resolved to everyone’s satisfaction. But let me provide a few of my observations, comments and “war stories.”
If you have spent time in Wichita, Kansas, you well know that it is usually windy there. Leaving the King Air on the ramp without restraints will almost always lead to aggressive propeller rotation. We at the Beechcraft Training Center – where I started my King Air career in 1972 – always emphasized the importance of installing the restraints if the airplane would be parked for more than 30 minutes or so. Yet, when
our students drove to lunch, what did they see on the factory ramp? They saw every new King Air sitting there with no restraints and the props turning like crazy! Right or wrong, the production test personnel had been directed not to worry about it, and they surely did not! Was harm caused? Probably no one knows the exact answer, but I’ll say this: I don’t think Beech ever received a warranty claim for RGB damage in a new King
SEPTEMBER 2024
KING AIR MAGAZINE • 23