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Driver170

Starter duty cycle

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Hope someone can expand on the actuall procedure and what it means?

 

Starter Duty Cycle :

First attempt ....................................2 min. ON & 20 sec. OFF -

Second & subsequent attempts. ..........2 min. ON & 3 min. OFF

 

2 mins ON - does that mean the GRD switch on for 2?

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2 mins ON - does that mean the GRD switch on for 2?

 

It means the starter can be on for a maximum of two minutes which must be followed by 20 seconds off before the next start attempt.

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So if you get an abnormal engine start wouldn't you place the starter to OFF anyway? Or are you going to leave it in GRD?

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It's stating it must be off for 20 seconds before another attempt. Rather then 5 seconds in off, try again, for example

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So if you get an abnormal engine start wouldn't you place the starter to OFF anyway? Or are you going to leave it in GRD?

 

It depends. If you have a hot or hung start or no EGT, I would motor the engine. If you had no N1 or N2, I'd simply go to OFF on the START SWITCH.

 

For no oil pressure, my book still says to motor it. Not so sure on that one, but that's what it says.

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Do you ever start the stopwatch for engine starts? What do you mean motor the engine? Is that keeping the start switch to GRD?

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The meaning of the procedure is simly not to overheat the starter system. Therefore you wait for cooldown after a failed start.

"Motoring" the engine means cranking it but not allowing fuel in. If a start failed fuel was likely injected in the combustion chamber. Motoring the engine will blow it out, otherwise it may cause anything from a hot start to a fire on next attempt depending on how much fuel accumulated!

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Do you ever start the stopwatch for engine starts? What do you mean motor the engine? Is that keeping the start switch to GRD?

 

I always do that. Start the timer once the valve is open (that way you'll know when the two minutes are over), also I note the time when I place the start lever to idle. That way you know (+10 sec) when EGT should increase at the latest. I assume not many do this, but it might be worth a thought at least.

 

Motoring the engine means running the starter, yes.

 

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Thanks alot guys! Does anyone have any good articles i can read on about all of this? Also the correct procedure when using the stopwatch for monitoring ?

So if i place the switch to GRD i can keep it at that position for 2 mins MAX ?

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I just turn the start switch and hit the timer at the same time. Easier in the plane than in the sim, I suppose. You could just use an actual stopwatch or your phone or whatever works.

 

This is one thing the sim can't do: simulate where your limbs go and the muscle memory from practice.

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So what exactly is max motoring is it where your leaving the start switch on and not moving the fuel lever to IDLE at 25% N1. So N2 would be at 28 ?

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Great link. Max motoring is reached when N2 does not increase by more than 1% within 5 seconds. A lot of sim videos and tutorials get this wrong and tell you to flip the fuel lever when N2 reaches 25% or 22% but that's actually not the right procedure and risks a hot start.

 

My method is to keep a close eye on N2 as the rate of increase slows, start counting the seconds each time the single digit (1%, not the tenths digit) turns over. If you get to 5 and you're still on the same digit, introduce fuel.

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A lot of sim videos and tutorials get this wrong and tell you to flip the fuel lever when N2 reaches 25% or 22% but that's actually not the right procedure and risks a hot start.

 

25% N2 or max motoring with a minimum of 20% if 25% is not achievable is what's in our manual.

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Michael yes! But looking for a good explanation on what that term means.

A lot of sim videos and tutorials get this wrong and tell you to flip the fuel lever when N2 reaches 25% or 22% but that's actually not the right procedure and risks a hot start.

 

Well there must be some wisdom in boeing saying that you need to put the start lever to idle at 25% or they would have mentioned to wait till the N2 reached max motoring

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25% N2 or max motoring with a minimum of 20% if 25% is not achievable is what's in our manual.

 

Yep.

 

25% or max over 20% = give it the gas.

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Well there must be some wisdom in boeing saying that you need to put the start lever to idle at 25% or they would have mentioned to wait till the N2 reached max motoring

 

I'm not sure Boeing do necessarily say that, however (which is the point being made by Andrew).

 

I don't know about the 737, but the relevant section of the B747 (RR) manual start procedure is:

 

Engine START switch .................................................... Pull P2
Verify that the N3 RPM increases. P2
When N3 is at 25%, or (if 25% is not possible), at maximum motoring:
FUEL CONTROL switch .......................................RUN
 

 

looking for a good explanation on what that term means.

 
Motoring = turning the engine over using the starter motor.
Maximum motoring = the maximum achievable N2 (or N3 for triple-spool engines) on the starter motor, i.e. when N2/N3 stops increasing.
 
EDIT: everyone else got there whilst I was writing this!

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Michael yes! But looking for a good explanation on what that term means.

You remind me of Nancy Kerigan.

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You remind me of Nancy Kerigan.

 

Haha why is that?

= turning the engine over using the starter motor.

Maximum motoring = the maximum achievable N2 (or N3 for triple-spool engines) on the starter motor, i.e. when N2/N3 stops increasing.

 

Good stuff simon

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So does max motoring vary depending on any conditions?

 

It can but the only time I have seen it reach max motoring below 25% is when starting with an external air cart.  Even then most carts will get you above 25% but sometimes you get a lousy one.

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Even then the NO. 2 Engine will be started with a cross bleed start.

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The Continental manual I have says start lever to idle at 25% or max motoring, which ever comes first.

 

Dave

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Even then the NO. 2 Engine will be started with a cross bleed start.

How do you suppose #1 got started? By air start cart or by...

 

Obviously you're going to get the required speed when conducting a crossbleed start. The same can't be guaranteed when air start carting the #1

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