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Engine warmup

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Engine warmup

Old 30th Jul 2019, 17:22
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Engine warmup

Engine warm up if shut down for less than two hours is 2 minutes at idle, if shutdown for more than two hours warmup is 5 minutes at idle.

Scenario: Engines have been shut down for 3 hours. Push back from gate, start both engines because it is required for initial taxi. After clear of congested area, shut down engine two (it has been running for less than 2 minutes) and continue taxi. What will be the warm up required upon restart of engine 2?

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Old 30th Jul 2019, 17:30
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Are you serious? Really?
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Old 30th Jul 2019, 18:10
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He seems to be🤯
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Old 30th Jul 2019, 18:31
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Originally Posted by CaptainMongo View Post
Engine warm up if shut down for less than two hours is 2 minutes at idle, if shutdown for more than two hours warmup is 5 minutes at idle.

Scenario: Engines have been shut down for 3 hours. Push back from gate, start both engines because it is required for initial taxi. After clear of congested area, shut down engine two (it has been running for less than 2 minutes) and continue taxi. What will be the warm up required upon restart of engine 2?
For you, 15 minutes, because one can never be too safe.....
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Old 31st Jul 2019, 03:19
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Scenario: Engines have been shut down for 3 hours. Push back from gate, start both engines because it is required for initial taxi. After clear of congested area, shut down engine two (it has been running for less than 2 minutes) and continue taxi. What will be the warm up required upon restart of engine 2?

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Old 31st Jul 2019, 05:01
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Why not keep it running for 5 minutes and THEN assess whether you need to shut it down?!? Do you REALLY need to make things MORE complicated?!?
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Old 31st Jul 2019, 08:32
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Ask yourself what you are trying to achieve - a warm engine prior to takeoff.

If your manual states 5 minutes to warm up a “cold” engine, then unless you have run the engine for that long prior to shutting it down again, I’d suggest you start the warm up timer again on the next start. Be conservative.

I would be a little suspect of the reason for shutting it down again so soon after pushback, hypothetical aside.

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Old 31st Jul 2019, 08:45
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What’s the increase in cost for nosewheel replacements ?
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Old 31st Jul 2019, 09:19
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OP, as You did not mention the type or general situation you are referring to, maybe You could write a few words on why a shutdown after clearing of the congested area is necessary or beneficial? Are you taxiing out for departure or are you referring to a mere relocation of the aircraft on the apron that is for whatever reason done under its own power and not by tug?

One thing that needs to be remembered as well is that not only fuel costs money, but so does an engine. A startup is not exactly easy on the engine and it may well be that the additional maintenance costs due to the number of startup/shutdown cycles racked up by this practice will be way larger than the possible fuel and brake wear savings...
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Old 31st Jul 2019, 10:20
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In case of a doubt, just be conservative: I will definitely go for the 5 min. 2 min more is not going to kill anyone.
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Old 31st Jul 2019, 16:34
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Originally Posted by B2N2 View Post
What’s the increase in cost for nosewheel replacements ?
Probably close to zero, especially after viewing all the skid marks going around tight taxiway turns or lining up on the runway. The additional side load on the nose gear is minimal in comparison. The amount of corrective inputs by the rudder tiller to compensate for the asymmetrical thrust is minor.
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Old 31st Jul 2019, 16:51
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Originally Posted by B2N2 View Post
What’s the increase in cost for nosewheel replacements ?
We know there’s a fuel savings. What’s the additional cost in brake wear on arrival when many of the aircraft will accelerate to 20+, or even 30+ kts, with all engines turning and burning at arrival weight?
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Old 31st Jul 2019, 20:45
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Several gate areas where we operate require a two engine taxi from the gate. After leaving the congested area, the taxi route can be 15 - 25 minutes, thus the engine shutdown. Monday I had a taxi which was 97 minutes gate to runway. How about a show of hands who would run two engines during that length of taxi. Once during that taxi we even shut down both engines for about 20 minutes, think of that. Then, to top it all off, we did a cross bleed to start number two.

Our outfits bean counters have run the numbers and have determined any engine shutdown, regardless of length, is money saving. I fly airplanes, the bean counters count beans, if that’s what they have determined that’s good enough for me. To those of you who have provided a thoughtful response, thanks.

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Old 31st Jul 2019, 20:59
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I don't consider 20 minutes a long time at all. I'd keep them both running. Having the PTU or yellow pump running is incredibly annoying from a passenger perspective, particularly for those seated nearest to those pumps (A320).

Obviously for a 90 minute taxi at JFK, I'd consider shutting one down, but again, the noise in the cabin for that length of time may give me pause. If I know the taxi will be that long, I'll request extra fuel. We may be too heavy to make a SE taxi practical anyway.
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Old 31st Jul 2019, 22:02
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Get a tug to pull you out a bit.

According to a knowledgeable CFM gentleman, up to 15 minutes warmup is still beneficial to the longevity of the engine, which translates well into direct fuel savings due to low(er) burn for long(er) time.

Though I understand you speak of IAE engines, which at least on the small bus really have a lot of ground idle thrust, pitty you cannot make it out on just one.

Towards the core of your question, I have nothing to add. It is an odd situation hence you came here with it. The suggestion with a tug is serious - beancounter's business as you have already pointed out.
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Old 31st Jul 2019, 22:20
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I thought I posted this earlier, but it didn't show up so I'll risk repeating myself.
The bottom line is that running at/near idle for a few minutes then shutting down for 90 minutes does not meet the requirements for having a 'warm' engine. Perform a minimum of a five minute warmup.
Setting takeoff power on an engine that isn't thermally stable is hard on the engine. The impact can be anything from a tip seal rub (permanent performance loss) to in extreme cases it can cause an engine surge.
Saving a couple of gallons of fuel by not doing a proper warmup will be quickly swamped by even a small increase in engine fuel burn until the next overhaul.
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Old 1st Aug 2019, 02:29
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Originally Posted by tdracer View Post
I thought I posted this earlier, but it didn't show up so I'll risk repeating myself.
The bottom line is that running at/near idle for a few minutes then shutting down for 90 minutes does not meet the requirements for having a 'warm' engine. Perform a minimum of a five minute warmup.
Setting takeoff power on an engine that isn't thermally stable is hard on the engine. The impact can be anything from a tip seal rub (permanent performance loss) to in extreme cases it can cause an engine surge.
Saving a couple of gallons of fuel by not doing a proper warmup will be quickly swamped by even a small increase in engine fuel burn until the next overhaul.
Yea but what do you know? You're not a beancounter

Thanks as always for your insightful contribution.

I've flown with people who must pride themselves in applying takeoff thrust and shutting down the engine right at the limits. Never understood it.

Last edited by Check Airman; 1st Aug 2019 at 03:02.
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Old 1st Aug 2019, 06:44
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Mechanical sympathy applies.

I once got to the staff carpark at the same time as a group of ground handlers. They obviously had some sort of private race going on, or were trying to beat the traffic. They each started their car engines and as soon as the engines caught, they all accelerated away like mad things.

Every one of their engines sounded like a bucket of bolts, i.e. worn to buggery because of working the engines hard before the oil was warm enough to circulate fully. Now, think of a gas turbine engine, parts of which are under much higher stress than a car engine, especially at take-off power.

As well as seals, and thermal stresses within the engine, the oil needs to be warm enough and fluid enough to get around the engine easily and quickly.
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Old 1st Aug 2019, 09:31
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Even at the risk of some thread drift:

Originally Posted by CaptainMongo
Monday I had a taxi which was 97 minutes gate to runway.
Now, the operational area I am familiar with is Europe and its closer surroundings, and I may not have come across the yet unmentioned airport that this took place on. However, this does strike me as exceptionally long - possibly longer than the subsequent flight. Does ATC allow startup and pushback without taking runway queues into account? Is there no CDM or "first come-first serve" queue along which startups are approved while both allowing sufficient taxi time and keeping the queues at the holding point somewhat within a reasonable limit?

Surely, such a system would be desirable from an efficiency, fuel saving and engine lifetime saving standpoint and beneficient to ATC and airlines alike? If you are not going to depart for another 90 minutes, why not wait at some parking spot with, possibly a remote one, with ground power and aircondition plugged in?
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Old 1st Aug 2019, 10:48
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Originally Posted by CaptainMongo View Post
Engine warm up if shut down for less than two hours is 2 minutes at idle, if shutdown for more than two hours warmup is 5 minutes at idle.

Scenario: Engines have been shut down for 3 hours. Push back from gate, start both engines because it is required for initial taxi. After clear of congested area, shut down engine two (it has been running for less than 2 minutes) and continue taxi. What will be the warm up required upon restart of engine 2?
Ok then. 5 minutes because whether or not you can 'credit' any of the "less than two minutes at idle" towards the requisite 5 minutes, is information you do not have.
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