What is that noise?

[Jason M Tutwiler]

So, I'm still fairly new to PSX but I've learned it enough that I've created my ideal situation.  I'm on the ground in a "cold and dark" state lined up with a local runway where I live.  However, I say cold n dark but I still hear a humming noise like an AC or something.  When I deselect the top three stereo buttons on the server under audio, the noise stops.  I've been searching the flight deck and can't find anything so I'm thinking its my custom model.  Anyone have any ideas?  It wasn't until I made modifications to an existing model that I ran into this.  I'm almost positive its equipment or programming on my 744 model and if it's not that, then it's probably a switch that I don't fully understand.  Also, I can't get the APU started.  For the noise or APU starting, I shouldn't need high or low pressure air or any GPU.  I know there's a switch on the far back panel that selects between transformation rectifier or Battery for the APU and I'm not clear on the differences.  At any rate, any assistance with the noise and my APU issue would be greatly appreciated!  Thank you in advance!

Regards,
Jason Tutwiler

[Avi]

Does your external Bleed Air or Conditioned Air in the Situation / Service page connected (it will make "noise" even on a cold and dark cockpit)?

How do you start your APU? Do you switch the selector from OFF to ON and with no delay to START and release without holding the selector for 2 sec? The APU won't start if it doesn't sense the APU air inlet door open.

[Holger Wende]

Hi Jason,

Not sure but it sounds as if something is spinning down, over time the frequency slowly goes down and the humming noise fasdes out.
I assume it's the standby attitude indicator which is spinning in the cold and dark situation.

Just wait a few minutes until the humming noise is gone, then save the situation again.

Regards, Holger

EDIT: Or wait until Instructor -> Analysis -> Navigation -> Stby attitude gyro RPM is 0
EDIT 2: Instructor -> Model -> Equipment -> select LCD standby instrucments and the hummming sound is gone immediately :-)

[Hardy Heinlin]

Here are 5 different examples of continuous noise when parked at the gate:

Select all three stereo sound groups on the Audio page.

Load the situ file Basic 028 - Parked and engine shutdown.situ

Overhead panel: Set EQUIP COOLING to OVRD
Effect: A certain hiss in the mid frequency range will fade out. This was the airflow from the equipment cooling system.

Overhead panel: Set all three PACK selectors to OFF.
Effect: All hiss is gone. This was the airflow from the air conditioning packs.

Overhead panel: Set EQUIP COOLING to NORM
Effect: The airflow just from the equipment cooling alone is now audible.

Overhead panel: Set EQUIP COOLING to OFF
Effect: All hiss is gone.

On Instructor > Model > Airframe select Aircraft model: "Passenger"
Effect: Another hiss noise is now audible.

Overhead panel: Set RECIRC-LWR to OFF
Effect: All hiss is gone. This was the airflow from the lower recirculation fans which you can hear on the flight deck of the passenger 747.

On Instructor > Situation > Time set the "Time acceleration" slider to 64.

Overhead panel: Pull the circuit breaker at grid position B25 under "ATTD IND"
Effect: A very high peep tone glides down. This is the gyro of the standby attitude indicator spooling down from 18000 RPM to zero. (Normally, the spool-down to 0 RPM takes several minutes.)

On Instructor > Situation > Time set the "Time acceleration" slider to 1.

On Instructor > Situation > Weather > EHAM set the "Precipitation" to None.
Effect: No raindrops anymore.


Summary:
1) Equipment cooling
2) Packs *
3) Recirculation fans
4) Attitude indicator gyro
5) Rain


Regards,

|-|ardy


* Externally injected conditioned air from the airport service is also audible. This can be activated on Instructor > Situation > Service with the checkbox "Conditioned air".

[John H Watson]

For the noise or APU starting, I shouldn't need high or low pressure air or any GPU.  I know there's a switch on the far back panel that selects between transformation rectifier or Battery for the APU and I'm not clear on the differences.  At any rate, any assistance with the noise and my APU issue would be greatly appreciated!

The APU has an electric starter. You will need the aircraft battery switch turned on (and a properly charged battery).
As Avi says, you will need to hold the APU selector in START for a second or two (to latch the starting circuits).