Twelve years after Continental issued service bulletin SB03-3 directing maintenance technicians to use a borescope to inspect each cylinder every time a compression test is performed, its instructions are being routinely ignored—at a high cost to aircraft owners.
A compression test is one of the valuable tools available to a mechanic to diagnose cylinder health, yet it requires a degree of skill to perform accurately and even the best techs admit that they may not get the same results twice in a row. Above all, it is only one tool in the tech’s arsenal and should never be used by itself to make the decision to pull a cylinder off an engine. Too often low compression accompanied by a leaking exhaust valve has resulted in a yanked cylinder only to find that the valve and its seat are perfectly healthy.