5/10 min limit
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From: various places .....
Now that's an interesting thought and one I'd not given too much attention to in the past. I would take the view that, if the flex T/O thrust setting is below METO/MCP then there is no limit, otherwise the normal T/O limit would be appropriate.
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Joined: Apr 2001
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From: various places .....
would you care to explain what do you mean with meto/mcp
My humble apologies - often one tends to forget that one's familiar jargon is not necessarily generic.
METO - maximum (power) except for takeoff
MCP - maximum continuous power
.. same sort of limit consideration as MCT = maximum continuous thrust.
The limit for continuous operation, albeit with a longer term maintenance cost impost .. ie, not to be used routinely or capriciously but, if you need it, use it.
My humble apologies - often one tends to forget that one's familiar jargon is not necessarily generic.
METO - maximum (power) except for takeoff
MCP - maximum continuous power
.. same sort of limit consideration as MCT = maximum continuous thrust.
The limit for continuous operation, albeit with a longer term maintenance cost impost .. ie, not to be used routinely or capriciously but, if you need it, use it.
Joined: Mar 2006
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From: -11 msl
I don't think it applies for the flex temp / MCT due to the fact the 5 / 10 min rule on a engine is needed in case of n-1 with performance limitations (heavy ac or high terrain). When using flex temp or assumed temp you are basicaly downgrading your engine.
Joined: Apr 2004
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From: Dorset UK
I think the limitations are written to keep it simple.
Remember Flex thrust could be only slightly below Max thrust.
The engines are not going to fall apart if you exceed these times but why would you want to exceed 5 mins on 2 (all) engines before reducing to MCT or less? The 10 min limit for engine out situations is to allow for your much reduced rate of climb.
I'm on A300 with GE engines, but the same limits apply.
Hope this helps.
Remember Flex thrust could be only slightly below Max thrust.
The engines are not going to fall apart if you exceed these times but why would you want to exceed 5 mins on 2 (all) engines before reducing to MCT or less? The 10 min limit for engine out situations is to allow for your much reduced rate of climb.
I'm on A300 with GE engines, but the same limits apply.
Hope this helps.
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From: various places .....
Keep in mind that in the early flex days, one saw thrust settings below climb thrust. QF, being one of the first, had a case where the crew complained to ops engineering that, on the call to set climb thrust .. the FE pushed the throttles up. Wal Stack, boss at the time, thought that a little strange so he imposed a limitation that flex would not be less than climb thrust. This tale he related when I was an undergraduate aero eng student and he was an Industry lecturer for one of our courses at Sydney.
Joined: Mar 2001
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From: I wouldn't know.
Still happens. Use derate 2 and a high ATM on a 737 and even climb 2 thrust will be higher than take off thrust. Of course nowadays the company wants us to select higher climb thrust anyway as it supposedly saves fuel.
Joined: Sep 2006
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From: any town as retired.
some one some where told me
that for example RR are required for certification purposes to run the engine at MAX thrust for 100 hours. So a 10 min burst of MAX thrust should not be a deal breaker.
Discuss.
glf
Discuss.
glf
Joined: Feb 2005
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From: flyover country USA
Cert tests are typically run in shorter cycles, so I seriously doubt anyone runs 100 hr at one time.
However, in principle Gulfstreamaviator's right. I've mentioned before that I've conducted ground runs - routinely operating at various T/O ratings, 30 minutes or more at a time continuously above MCT. My conclusion is that extended time at T/O is not a safety issue, so 5 min. vs. 10 min. isn't a factor - EXCEPT in the regulator's eyes.
However, extended time at T/O is an economic issue, and performance deterioration (increased fuel burn, etc.) is aggravated by holding T/O longer than necessary for the mission.
However, in principle Gulfstreamaviator's right. I've mentioned before that I've conducted ground runs - routinely operating at various T/O ratings, 30 minutes or more at a time continuously above MCT. My conclusion is that extended time at T/O is not a safety issue, so 5 min. vs. 10 min. isn't a factor - EXCEPT in the regulator's eyes.
However, extended time at T/O is an economic issue, and performance deterioration (increased fuel burn, etc.) is aggravated by holding T/O longer than necessary for the mission.
Joined: Sep 1999
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From: ME
Do not confuse the engines capability with the legal requirements. If you are using Flex as your takeoff thrust, then you can only PLAN to use it for 5 or 10 minutes (depending on which option you purchased). Also remember that your takeoff performance is based upon that thrust rating and there is no requirement to increase the thrust in the event of an engine failure.
Mutt
Mutt
