Review of Helicopter Engine Instruments 

by:  Paul D. Faltyn – Commercial Pilot and A&P Mechanic

A common misleading scenario concerning engine instrumentation among piston engine helicopter operators is that you do not repair or calibrate them unless they fail or there accuracy is suspect. All mechanically driven instruments have a ( TBO ) ” time between overhaul “, most manufacturers recommend that there instruments be overhauled between 1500 to 2500 hours in service.

Engine and Rotor Tachometers: 

The engine and rotor tachometer have bearings, motors, springs, pivots, and mechanical linkages that are subject to vibration, temperature changes, and wear. As the internal lubrication break downs, spring tension changes, parts wear, the pointers can become sluggish, sticky, or loose calibration.

I would suggest that at every engine overhaul or 1200 hours the calibration should be verified and overhauled at 2500 hour intervals per most manufacturers specifications for TBO.