Aural warning during autostart 747-400

[AnthonyGA]

I hope this is the correct forum for this question.
What would cause an aural warning (like "whoop-whoop-whoop" one time) when an engine is autostarted on a 747-400, either when the start switch is pulled or when the fuel cutoff is set to run? I can't find anything about it in the operations manual. I thought maybe yaw damper settings had something to do with it, but that doesn't seem to matter. Or maybe duct pressure. I don't know. Maybe the real aircraft doesn't ever sound such a warning (?).

[FlyerFoto]

I take it we are talking FlightSim here?

[AnthonyGA]

Specifically, Microsoft Flight Simulator 2004, but with the 747-400 add-on aircraft simulation sold by Precision Manuals Development Group (PMDG), which is renowed for its realism and completeness (quite different from the default aircraft).

Since this behavior would have to be specifically written into the simulation, I assume that the developers were trying to emulate a real-world behavior of the autostart system. However, I can't find anything in the (real-world) operations manual for the 747-400 that describes this aural warning or explains what causes it.

I start engines in the recommended sequence of 4, 3, 2, 1. I never seem to get the warning on 4 or 3, but sometimes I get it on 2 or 1, or both. The engine still starts with no anomalies that I can see. There are no EICAS messages.

If it never happens on the real aircraft, I'll just ignore it (while puzzling a bit over why the simulation includes it). If it does happen on the real aircraft, I'd like to know why, just for the sake of better understanding the aircraft (which is the whole point of simulation, after all).

[spoilers yellow]

after 4 and 3 start you get an EICAS advisory for the aux hyd demand pumps when the main hyd pumps come on line, but you shouldnt get the aural warning as its advisory only. does your flight sim know the difference between advisories and cautions (which would generate an aural warning). Other than that you shouldn't get any aural warnings or eicas cautions during a normal two engine autostart.
very occasionally the eng generators for 1 or 2 dont automatically come on line as the engs start, if this was the case you would get a aural and EICAS caution, but certainly not normal and i doubt flight sim would have that problem. I assume you have all gens etc in the correct postions for start? any other selections should only produce advisories and hence no aural warning.

[AnthonyGA]

Thanks for the pointers; that gives me something to check next time. I'll watch the EICAS while starting (a bit awkward in the sim, but possible).

I've seen yellow notations on the EICAS before after engine start that disappear after a moment, but since it's hard to watch the overhead panel and an EICAS display at the same time, I don't know if they occurred simultaneously with the aural signal. I'll watch both henceforth just to see if something appears the next time I hear it.

From what I gleaned from the sim documentation and real-world docs, I autostart an engine with engine bleed ON, fore and aft fuel pumps for that engine ON, engine hydraulic pump ON, demand AUTO, generator ON, fuel cutoff ON, and finally engine start button pulled (some sources say I should pull the start button first and then cutoff, but maybe it doesn't matter for an autostart). I do this identically for each engine. Numbers 4 and 3 usually start silently, but sometimes I get the aural signal for 2 and 1.

I'll report whatever I find out, and then perhaps someone can tell me if the sim is behaving like the real thing. I'll try some manual starts, too, to see if that makes any difference.

[spoilers yellow]

before eng start make sure you have all fuel pumps on (for tanks that have fuel in them)
no 1 and no 4 hyd demand pumps in aux (if fitted ) or auto
all eng bleeds on
all packs off
autostart switch on

to start the engs, pull the 4 and 3 start switches and put the feul control switches to run and watch the eicas.
you should get no cautions or advisories until the 4 and 3 eng are running when you will then get hyd advisories with no aural.

start 2 and 1 together in the same way.

after all eng running, turn apu off

put all hyd pumps to auto
put packs on.

in real life that will produce no aural or eicas cautions.

[AnthonyGA]

Thanks. I'll try it and see if the sim behaves correctly.