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av8r13

2nd flight engine start

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no issues starting engines on the first flight.

however, after completing the first flight, i can only start 1 engine. i continue to get "hung" starts on all but 1 engine

is this a bug or am i doing something wrong. on APU with duct pressure reading normal

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37 minutes ago, av8r13 said:

no issues starting engines on the first flight.

however, after completing the first flight, i can only start 1 engine. i continue to get "hung" starts on all but 1 engine

is this a bug or am i doing something wrong. on APU with duct pressure reading normal

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signature added.

any ideas why i ak having issue starting issues on my second flight?

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Maybe you are not waiting long enough for the start.  When you say it is hung, you mean that it winds up to a certain N2 and then stays there?  This is normal for this engine when it is warm.  The EEC will 'motor' at something like 28% N1 (I think) to cool the engine to prevent the N1 shaft from being out of balance due to uneven heating of the shaft, which would be bad on the engine if that shaft wobbled. 

Let the EEC do it's job, you should get a start after about 50 sec or so.

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29 minutes ago, downscc said:

Maybe you are not waiting long enough for the start.  When you say it is hung, you mean that it winds up to a certain N2 and then stays there?  This is normal for this engine when it is warm.  The EEC will 'motor' at something like 28% N1 (I think) to cool the engine to prevent the N1 shaft from being out of balance due to uneven heating of the shaft, which would be bad on the engine if that shaft wobbled. 

Let the EEC do it's job, you should get a start after about 50 sec or so.

Very true. It took a while to get used to this  in the 747, coming from a previous airplane that spooled up quickly and we had to monitor and abort for hung starts. Sometimes the 747 can take a while, and with autostart you just sit and watch until it says something is wrong. Definitely a concept that took some getting used to. 

Edited by Jetlinker

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2 hours ago, downscc said:

Maybe you are not waiting long enough for the start.  When you say it is hung, you mean that it winds up to a certain N2 and then stays there?  This is normal for this engine when it is warm.  The EEC will 'motor' at something like 28% N1 (I think) to cool the engine to prevent the N1 shaft from being out of balance due to uneven heating of the shaft, which would be bad on the engine if that shaft wobbled. 

Let the EEC do it's job, you should get a start after about 50 sec or so.

During engine Autostart, whenever the EEC detects a hot or hung start before Starter cutout the best thing to do is sit on your hands and wait and see what happens.  With either of these two conditions the EEC will automatically cut off the ignition and fuel to the engine and then continue to motor it over until the EGT is equal to or less than 100degsC.  It will then apply fuel and use both ignitors for a second attempt.  If there is no EGT rise detected during the second attempt within 20 seconds of the fuel being re-applied then the EEC will cut off the fuel again and motor the engine for 30 seconds.  If these two autostart attempts are unsuccessful then the EEC will abort the autostart sequence and an EICAS Caution message ENG AUTOSTART will be displayed until you physically select that engine's Fuel Control Switch to Cutoff. 

Edited by berts

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17 hours ago, berts said:

With either of these two conditions the EEC will automatically cut off the ignition and fuel to the engine and then continue to motor it over until the EGT is equal to or less than 100degsC.

Interesting, our FCOM discusses that when shutdown has been for 45 - 360 minutes and EGT > 30C, motoring is extended for 40 sec when N2 reaches 20%.  Apparently there are different EEC software versions.

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Also the -8i engines have a Bowed Rotor Start Mitigation procedure if restarting within 30min to 6hrs. In a nutshell, after a flight - long or short - upon shutdown the core of the engine can get heat-soaked, and the top rotors in the hot section can get out of whack (yes, that's a technical term - lol). The recommendation is to 'dry motor' the engines for a few minutes (and you can do 2 at a time to quicken things up) thus removing excess heat and evening-out the heat that remains. Not entirely essential, but folks assure me it definitely decreases wear on the engines!

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5 hours ago, downscc said:

Interesting, our FCOM discusses that when shutdown has been for 45 - 360 minutes and EGT > 30C, motoring is extended for 40 sec when N2 reaches 20%.  Apparently there are different EEC software versions.

Hardly surprising really, because of the different makes of engine fitted to all B747's.  Incidentally, what I described covered the RR engine's EEC behaviour for a single Autostart sequence and not what happens after a normal shutdown.

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18 hours ago, berts said:

Hardly surprising really, because of the different makes of engine fitted to all B747's.  Incidentally, what I described covered the RR engine's EEC behaviour for a single Autostart sequence and not what happens after a normal shutdown.

Ah yes, okay.... I was referring to specifically the -8 engines and reiterated by Patrick.

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