Life Limited Parts: Block time or Air time?

[oceancrosser]

A question for the maintenance guys (haven't got a clear answer from the guys at my airline).

For LLPs, is block time or air time (flight time) used? Granted the a/c is not flying during long taxis or gate-holds, but one (or more) engines are running.

So, which is it?

[PDR1]

Whatever it says in the Operations manual of the relevant CAMO for the aeroplane. Each operator will have its own procedures (usually informed by DAOS recommendations) to best suit its own fleet and circumstances.

[westhawk]

In general, the recording of time and/or cycles counted against life limited parts, the following conventions are most often used:

Airframes and Engines (generally): Flight time is time operating in the air and cycles are takeoffs/landings.

APUs and certain other onboard equipment: Time and operating cycles is counted only when said equipment is actually operated, irrespective of flight time/cycles.

Airframes, engines and APUs will each have their own logbook. Some component parts of these will be tracked within the applicable logbook or approved electronic file system rather than on a life limited parts list. Both the LLP and periodic inspection items will be tracked as a part of the ongoing maintenance record-keeping system.

For example:

Engine fan hub: Let's say a particular fan hub has a 20,000 cycle life limit. This hub would have a cycle counted against it every time the engine has one counted against it. At 20,000 cycles it must be removed from service. This is different than certain parts which must be inspected or reworked at a certain number of hours or cycles. Those parts requiring periodic inspection will be included and tracked via the inspection schedule rather than the LLP list.

Oddities:

Some engines only have a cycle counted against it when the airplane actually flies, while others may count a cycle against it when operated above a particular RPM or temperature. So starting and shutting down an engine on the ground may or may not count as a cycle dependent on how hours/cycles are to be counted for a particular type certificated engine. How cycles and hours are counted is established as a part of the type certificate approval process, so may vary between different types. Clear as mud? Well it gets more complex than that, which is why one universal method is not necessarily applicable to all.

Maintenance managers can and do have a large influence on safety and operating cost by how well they plan required maintenance events!

[galaxy flyer]

Generally, in FAA World, engines and airframes are logged by take-off to landing.