I was wondering, how is a jet engine time measured. I fly 172's, so I pay based on the hobbs hour and I'm pretty sure my club uses the tach hours on the tachometer for their oil changes or the 2000 hour overhaul. But do turbo fan engines have a similar concept. Because if a particular aircraft is flying to busy airports such as Boeing 747, it'll accumulate plenty of hours just idling and waiting for take off. Do they have some thing similar to hobbs and tach on the piston engine aircraft.
Jet Engine Time Measurement
- Thread starter rajsingh
- Start date
BobDDuck
Island Bus Driver
A lot of things on aircraft work in "cycles". One cycle is a take off and a landing. There are also hobbs like devices on turbine engines that keep track of the hours it is running.
A lot of places that don't do their own engine maintenance work have a "power by the hour" plan with who ever does it. So basically you are paying by the hour. Some places also have a setup where you pay by the number of uses. Before fuel got expensive our plan was per use, so the company policy was to leave the APU running unless you wouldn't need it for more than 30 minutes. So on short flights we left it on. Now, with fuel more expensive we've switched to a pay per hour plan and they want us to shut down they APU as soon as we don't need it.
A lot of places that don't do their own engine maintenance work have a "power by the hour" plan with who ever does it. So basically you are paying by the hour. Some places also have a setup where you pay by the number of uses. Before fuel got expensive our plan was per use, so the company policy was to leave the APU running unless you wouldn't need it for more than 30 minutes. So on short flights we left it on. Now, with fuel more expensive we've switched to a pay per hour plan and they want us to shut down they APU as soon as we don't need it.
In ours we have a flight hour meter (hobbs) wired to the squat switch. We also use the time off/on from the GPS. The charter company takes that information and bills the customer. They don't pay for engine-running-taxi time but I'm sure a "fudge factor" is built in to the flight time charges.
That's also how we track maintenance. In addition to cycles.
-mini
That's also how we track maintenance. In addition to cycles.
-mini
Orange Anchor
New Member
A lot of the components are 'on condition'. IF the engine meets parameters, it just continues on. For example, CFM has a press release now quite old where a CFM-56 remained on the wing for more than 40,000 hours and 17,000 cycles.
The engine can often be rated at different levels of thrust. And if an engine gets a bit tired at the high thrust level, the operator has the option to 'derate' the engine. This is not to be confused with using an 'assumed temperature'. Both procedures allow the engine to burn at a lower temp and thus increases engine life.
Finally, in some cases when an engine begins tiring, you may have some restrictions to comply with. For example, some of the CFM-56s had a limit that on the first flight of the day, you had to 'heat soak' the engine which meant idle for about 10-15 minutes. This was difficult to explain to the pax when everyone else is taking off and you have to tell the pax you're 'warming the engine up."
Polar742
All the responsibility none of the authority
The last few jets I flew, most had a CMC, or Central Maintenance Computer, and a form of Electronic Engine Controls (EECs or FADECs).
Engines with that type of control system record a broad array of data and down load it to the CMC. Some obvious data are things like the time the engine starts, the time it is shut down, as well as the number of start cycles.
Also they record a large number of other parameters such as the highest EGT during the start, the takeoff power used, the max EGT during take off, the amount of time the takeoff power was used, the climb power, and a "snapshot" of all the parameters, usually during a specific point during a takeoff run (say 100 kts) and during cruise.
All this data is loaded into a program and it spits out the date on which the engine should be due for an overhaul (should there be no FOD damage or other issue with the parts and pieces).
APUs typically have a cycle counter and a hobbs meter attached to them to measure usage.
Of course all that data is used just like Bob and Orange Anchor said.
Engines with that type of control system record a broad array of data and down load it to the CMC. Some obvious data are things like the time the engine starts, the time it is shut down, as well as the number of start cycles.
Also they record a large number of other parameters such as the highest EGT during the start, the takeoff power used, the max EGT during take off, the amount of time the takeoff power was used, the climb power, and a "snapshot" of all the parameters, usually during a specific point during a takeoff run (say 100 kts) and during cruise.
All this data is loaded into a program and it spits out the date on which the engine should be due for an overhaul (should there be no FOD damage or other issue with the parts and pieces).
APUs typically have a cycle counter and a hobbs meter attached to them to measure usage.
Of course all that data is used just like Bob and Orange Anchor said.
TFaudree_ERAU
Mashin' dem buttons
Also, if you use any sort of Automatic Power Reserve system in the event of an engine failure, you log it as an additional number of cycles.
In our Hawker with Garrett TFE-731-5BR engines, an APR activation counts as two additional cycles.
Some idiots have been known to use APR as a performance boost with both engines running instead of its intended purpose.
But as stated earlier, most time is logged when the wheels are up. Our FMS has a handy little feature that automatically logs the flight and it will actually display the appropriate page when the wheels touch down, even without you pressing any buttons. We jot the times down, and then enter them into an excel spreadsheet. I send them off to our mechanic and then he returns a "due list" to let us know when the next maintenance items are coming due.
In our Hawker with Garrett TFE-731-5BR engines, an APR activation counts as two additional cycles.
Some idiots have been known to use APR as a performance boost with both engines running instead of its intended purpose.
But as stated earlier, most time is logged when the wheels are up. Our FMS has a handy little feature that automatically logs the flight and it will actually display the appropriate page when the wheels touch down, even without you pressing any buttons. We jot the times down, and then enter them into an excel spreadsheet. I send them off to our mechanic and then he returns a "due list" to let us know when the next maintenance items are coming due.
jdlilfan
Well-Known Member
Even the Cessna Caravan has a "black box" on the engine to record engine use/ parameters for MX.