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MINHAS866

why the engines be started in low speed ground idle?

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hi to all can any body know breifly about that why herk engine s are started in low speed ground idle is there any technical reason .because before starting check list in -1 sec 2 says to put the button low. i never heard or read that we can start engine in normal. if it cannot be then why ?

Feed back will be really appreciated thanks:)

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The engine will start just fine in HSGI however there are limitations that need to be met at LSGI. (Oil press mins, Hydraulic min press) but main reason is to allow for a warm up period. With colder oil temps Engine Oil pressure could exceed 100 PSI (the pump is regulated but...) in the engine and damage the bearing seals. The Gearbox oil pressure will exceed the upper limit however the excess pressure is dumped back into the gearbox to prevent damage.

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hi minha5866 i believe it's for saftey reasons, so if the brakes fail or are not set, the airplane won't due an immediate left turn and plow into a building . like what happened to a friend of mine, also what natops said + your ensuring your 5th & 10th stage bleed valves are working properly eliminating the possibility of a hot, hung or stalled start thanks frank thomas

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The engine will start just fine in HSGI however there are limitations that need to be met at LSGI. (Oil press mins, Hydraulic min press) but main reason is to allow for a warm up period. With colder oil temps Engine Oil pressure could exceed 100 PSI (the pump is regulated but...) in the engine and damage the bearing seals. The Gearbox oil pressure will exceed the upper limit however the excess pressure is dumped back into the gearbox to prevent damage.

sir bundle of thanks

agreed as you said about oil temperatures low causing the the pressures to rise and warming up of the engine if the start is subsequent just after 15 to 30 minutes with no tendency of pressure rise(engine s are already warm up) can we start in normal

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sir bundle of thanks

in start in low noise level reduced for ground ops and maintenance cost reduced and increase service length of the equipment( bearing gears etc) agreed ?

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Yes you can start in HSGI,

You will reduce the cost due to lower fuel flow rates as well as reduce noise using LSGI. Service life in my opinion will be unaffected as they are designed to withstand much higher stress loads than those when operated at HSGI. In theory yes but real world application most likely no improvement in service life( in my opinion)...

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Minha I was always told opinions are like fannies everyone has one! As is said today back in the day you used low speed ground idle to keep from blowing the girls watching mini skirts up!

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Minha I was always told opinions are like fannies everyone has one! As is said today back in the day you used low speed ground idle to keep from blowing the girls watching mini skirts up!

:lol: hahaha

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When I was on A models we always started them in Normal Ground Idle...;) just seemed the right thing to do ,ha ha. Bill

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I was told that cutting fuel for LSGI and the 103.5% fuel cutoff come from the same place in the fuel control. So by starting in LSGI you're also double-checking the fuel control in case of a severe prop overspeed.

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The LSGI and Fuel toping do come from the same place, the LSGI reset changes the tension on the governor to set the speed. I guess you could say it "checks" the fuel toping but not really (IMHO) but it does check to see if the valve is moving towards the reduce fuel position so I can see how it could be said it checks toping. Works for me...

 

Me likes Spectre's reply!!!.... Normal Ground Idle...;) just seemed the right thing to do ,ha ha. Bill

Edited by NATOPS1

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I was told that cutting fuel for LSGI and the 103.5% fuel cutoff come from the same place in the fuel control. So by starting in LSGI you're also double-checking the fuel control in case of a severe prop overspeed.

​I agree this can be an indicator of fuel control health, but please don't take it for more than it is. Even if the engine will low speed, you never know if the fuel governor is correctly set anyway without doing the correct ops check, so the LSGI operation is of low value as an indicator you have overspeed protection. Maintenance performs the ops check every HSC and ISO, so you should be covered. Sure, something could break in-between, but it's not as simple as that. The flyweights that tell the governor it is overspeeding are the same flyweights that assist the speed servo valve to increase fuel flow during engine starting, so if that mechanism were malfunctioning, you would likely see more severe issues with fuel flow. The only fuel governor components not needed by the speed servo valve are a spring and a shaft.

The only true ops check for fuel cutoff is to do a fuel governor/pitchlock check. If the you are willing to tail swap for an engine that fails to low speed, you should be prepared to allow maintenance to do an official ops check of the fuel control to prevent a tail swap, especially when the LSGI solenoid is exempted on the MESL. In my experience, the entire LSGI system is infinitely less reliable than the fuel governor system. By all means, call maintenance out, but please, let us do an official ops check before refusing the aircraft.

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​I agree this can be an indicator of fuel control health, but please don't take it for more than it is. Even if the engine will low speed, you never know if the fuel governor is correctly set anyway without doing the correct ops check, so the LSGI operation is of low value as an indicator you have overspeed protection. Maintenance performs the ops check every HSC and ISO, so you should be covered. Sure, something could break in-between, but it's not as simple as that. The flyweights that tell the governor it is overspeeding are the same flyweights that assist the speed servo valve to increase fuel flow during engine starting, so if that mechanism were malfunctioning, you would likely see more severe issues with fuel flow. The only fuel governor components not needed by the speed servo valve are a spring and a shaft.

The only true ops check for fuel cutoff is to do a fuel governor/pitchlock check. If the you are willing to tail swap for an engine that fails to low speed, you should be prepared to allow maintenance to do an official ops check of the fuel control to prevent a tail swap, especially when the LSGI solenoid is exempted on the MESL. In my experience, the entire LSGI system is infinitely less reliable than the fuel governor system. By all means, call maintenance out, but please, let us do an official ops check before refusing the aircraft.

​What Lkuest said... ;-)

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