Engine Start Problem

[vhrob 2]

After all the appropriate pre-start preliminaries I move the fuel control to run. I get a reading for the EGT and the EPR, but nothing happens with N1.

What might I have omitted to do?

Rob

[Ephedrin 418]

Engine bleeds on?

packs off?

Edited March 22, 2018 by Ephedrin

[vhrob 2]

 

2 packs off, and APU Bleed on.

[Ephedrin 418]

I'm not entirely sure but I believe the engine bleed valves have to be open too on the 747.

[vhrob 2]

Thanks, I'll give it another try!

[berts 97]

20 hours ago, vhrob said:

After all the appropriate pre-start preliminaries I move the fuel control to run. I get a reading for the EGT and the EPR, but nothing happens with N1.

What might I have omitted to do?

Rob

First, make sure you have no faults enabled.  Check your Electronic Engine Control (EEC) switches are set to Norm, the Autostart switch is ON and the Standby and Auto IGN switches are both set to NORM. Assuming you are going to use the APU to start the engines make sure both APU generators are online, check the APU Bleed Air Isolation switch is set to ON; check both Wing Isolation Valves indicate open and turn all three A/C Packs to OFF.  At airfields close to sea level (<2,000ft approx) you will have sufficient air to be able to autostart two engines at a time (normally 3&4 and then 1&2) by first pulling the engine start switches (did you do this?) followed by their respective fuel control switches.

If there is an autostart problem then (apart from no oil pressure) the EEC will normally detect it and cut off the fuel and ignition before it makes a second attempt. Incidentally, during an autostart the EEC automatically opens the start and engine bleed air valves, even if the latter are selected OFF.

Bertie Goddard    

[kevinh 409]

I doubt it's the start procedure being used. If you have EPR and EGT responding then the start procedure is working, but not on all parts of the engine model. Part of the engine model responding, part not sounds like the problem reported in this NGX thread, which was FSUIPC related.

I suggest trying without any FSUIPC connections or assignments to the engine fuel switches.

[Qavion2 39]

13 hours ago, berts said:

during an autostart the EEC automatically opens the start and engine bleed air valves, even if the latter are selected OFF.

Bertie, I don't think this is correct.  The EEC has no control over the PRSOV.

My books say that the logic inside the ASCTU for the PRSOV "reverse flow" solenoid (which allows the APU bleed air to go backwards through the PRSOV) and the PRSOV "open" solenoid need to see the fire switch handle in and the ENG BLEED switch depressed. Start switch and N2 (or N3) speedcard signals are also required for the reverse flow solenoid.

Nothing will flow through a PRSOV without the respective Eng Bleed switch being armed.

 

Cheers

JHW

[berts 97]

9 hours ago, Qavion2 said:

Nothing will flow through a PRSOV without the respective Eng Bleed switch being armed.

Cheers

JHW

Double checked my Tech notes and they state "during an autostart the EEC automatically opens the start and engine bleed air valves".  However, you are right about the Eng Bleed switch needing to be armed for this to happen. Sorry about that.

Bertie

[Qavion2 39]

 

13 hours ago, berts said:

Double checked my Tech notes and they state "during an autostart the EEC automatically opens the start and engine bleed air valves".

I would still challenge the Tech notes' definition of "engine bleed air valves", Bertie. Just pushing the ENG BLEED switch will enable the PRSOV open solenoid. Pulling the start switch with the N2 below 50% will enable the PRSOV's reverse flow solenoid.

It's then up to the EEC to open the start valve, turn on fuel, etc, if the Autostart switch is on.

I have the PRSOV logic diagram, but it's not easy to read and probably copyrighted. I can't see any signal path from the EEC to the PRSOV (RR/GE).

Cheers

 

[Budbud 227]

On 22/03/2018 at 3:07 AM, vhrob said:

After all the appropriate pre-start preliminaries I move the fuel control to run

Hi,

Silly question but do you pull the engine start switch on the overhead before moving the fuel control to run? You haven't stated it.

[kevinh 409]

It doesn't matter which order you do it in an autostart, Romain. Both switches need to be operated before the start begins.

[Budbud 227]

Kevin,

The thing is the OP didn't stated whether he pulled the engine start switch at all. He just said he moved the fuel control to run after the before start flow and the engine start switch action is not part of the before start flow but of the engine start flow.

Edited March 27, 2018 by Budbud

[kevinh 409]

True, he didn’t mention a lot of things. As he saw a response in EGT and EPR that suggests he did operate the start switch, but I agree that is not certain. 

He hasn’t been back to the thread recently. The problem might be resolved.

[berts 97]

On 3/26/2018 at 7:54 PM, Budbud said:

Hi,

Silly question but do you pull the engine start switch on the overhead before moving the fuel control to run? You haven't stated it.

In the case of Rolls Royce engines, always select the start switch first followed by the fuel control switch for both an auto or manual start .  Why?  Because this is the correct sequence necessary for a manual start. It also enables the pilot to monitor either start sequence whilst keeping his hand on the fuel control switch, ready to immediately select it to off in the event of an engine start problem (eg no oil pressure) followed by the appropriate QRH procedure. Moving the Fuel Control Switch to CUTOFF will abort the Autostart. 

For an Autostart, pulling the start switch out arms the engine bleed air and start valves. Moving the fuel control switch next to RUN will initiate the autostart sequence and open the spar and engine fuel valves. The EEC opens the start and engine bleed air valves and the Start Light illuminates.  When the N3 increases to max motoring the EEC then opens the fuel metering valve and energises the selected igniter (normally one on the ground and both for an in-flight start). 

For a Manual Start (i.e. with the >AUTOSTART OFF message displayed), pulling the start switch out opens the engine bleed air and start valves and the start light illuminates. The Fuel Control switch is then moved to RUN, but not until the N3 has increased above 25%N3. The spar, fuel metering and engine fuel valves will open and the selected igniter will energise.

Starter cutout normally occurs automatically at 50% N3 in both cases.

Bertie