What does “on watch” mean for an aircraft engine and why it is important.
The reliability of aircraft engines is a complex task to monitor as the engine itself has several different metrics that we can utilise for reliability and monitoring purposes including the following:
– Oil Consumption
Engine parameters such as:
– EGT (Exhaust Gas Temperature) Temperature at different power settings
– Core Speed’s (N1, N2, N3 (dependant on engine))
– Vibration
– Borescope Inspection
– Oil Debris Monitoring (Magnetic Chip Detectors MCD or other Debris Monitoring)
– Visual observations
It is important to consider these factors toward engine reliability monitoring; typically, a reliability or monitoring program managed by the responsible CAMO and can place an engine “on watch” based on any of the monitored parameters exhibiting a change or non-normal behaviour in accordance with their reliability program.
Some events such as N1 vibration trending up, might result in an engine being placed “on watch”. For example, a subsequent fan blade relubrication / balance might then see the vibration drop back to normal levels results in the engine being taken “off watch” so it is possible to have engines return to normal parameters following corrective actions.
Parameters can “trend” which means they increase/decrease over a period of time, or we might observe a “shift” which is a more evident change over a short or immediate period of time. For example, EGT might “trend” upwards, or it could “shift” – a “trend” might be an indication of deterioration internally over time, where a “shift” might be an indication of a failure or event (bird strike / FOD etc).
If an engine is “on watch” or has been “on watch” recently it is important to consider the reliability data for the engine and look at the recent trend analysis along with a review of any maintenance carried to rectify – engine overhaul and repairs can be very costly for the responsible party.
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