So I was playing around with the systems last night. I was trying to shut down the recirc. fans while doing the pre-flight as they are quite loud. When pressing the recirc. fan switches to off, it doesn't seem to shut them off, or at least if it does, the sound still appears to have them running. The only way it seems to shut them off(at least soundwise), is to shut off the utility buses. After reading the manual, I'm under the impression that they can be turned off by either the recirc. switches or by the utility bus switches. Am I right on this, or is the noise I hear another fan that the utility bus operates? I know it works this way on the NGX. Otherwise there really wouldn't be a point of even having recirc. fan switches if they don't do anything.

 

Regards,

Rob

 

 

Am I right on this, or is the noise I hear another fan that the utility bus operates?

 

Equip cooling. Set it to override and things will get a bit quieter.

Wow, didn't realize the equip cooling fans were that loud. Seems like in other aircraft (737,757/767, etc.), the equip. cooling fan is incredibly loud in the cockpit. Good to know you all got it right though!

 

Regards,

Rob

Hi Rob, 

 

The sounds you are refering to arent actually the recirc fans - but instead the sound of the airflow coming from the cockpit ducts.  Then we vary the volume of these sounds in relation to a number of factors like duct pressure and equipment like the packs and recirc fans and also other parameters as well.

 

 

When I put my car aircon on full it sounds pretty much just like that. Shearing sound of air leaving the vents and ducts.