Questioning how limits are set

Measuring a machinery health parameter in a condition monitoring program is only half of the equation; at some point a limit must be set that initiates either further intensive monitoring or maintenance action. Limits are a fundamental and critical component of an effective condition monitoring program (often an integral part of a HUMS) and they can directly impact aircraft availability (e.g. rotor track and balance checks), or result in substantial maintenance burden (e.g. removal of machinery for overhaul based on wear debris). Limits therefore need to have a solid basis and often this is unknown, unclear or is questionable resulting in sub-optimal performance of the condition monitoring program.