Page 17 - Volume 15 Number 12

Engine Vibrations
Anything that spins generates a vibration whether it’s a propeller or a gearbox, if it spins smoothly the normal vibration is minimal. If it is out of balance, the vibration is more pronounced. Over time, the friction between moving parts creates excess play and the spinning becomes wobbly. This is where good vibrations go bad.
When you bring an engine to full power there are many associated components operating simultaneously. The starter generator, the fuel control, and oil and scavenge pumps are a few examples. These accessory components operate at a specific frequency (RPM) and each one generates a vibration. As a component begins to wear out, it is somewhat out of balance while spinning – the RPM is the same but the vibration increases. A worn-out component, still spinning at the same RPM is vibrating intensely and on the way to failure.
An engine vibration analysis (engine vibe survey) detects the vibrations generated by each component. Periodic surveys, done within the same operational parameters, can pinpoint an issue as it develops, and allows the problem to be monitored and fixed before it becomes serious.
Going Past TBO
Federal Aviation Administration (FAA) Part 135-regulated operators can’t run engines past TBO unless they are on an FAA-approved program. For King Airs (other than the B100), it is the MORE program which stipulates that an engine vibration analysis must be done on each engine at 400-hour intervals.
Many King Air owners operate under Part 91 regulations and therefore aren’t required to overhaul their engines at 3,600 hours, nor are they required to put their engines on an FAA-approved alternative maintenance program. Inspections are required (i.e., the Hot Section Inspection) but overhauls become optional.
The decision to run your engines past TBO is one that Part 91 operators should not take lightly. Going on the MORE program is one alternative. It lays out a very thorough and precise schedule of maintenance tasks for each engine, some as frequent as 50-hour intervals.
Most owners I deal with are Part 91 operators and many are running their engines past overhaul. They just keep plowing along because they trust the PT6As on their King Air. They know them to be an extremely reliable
DECEMBER 2021
KING AIR MAGAZINE • 15