DanielBednar
Topic Author
Posts: 13
Joined: Fri Jul 05, 2019 5:40 pm

Recirc Fans/ engine start

Thu Jul 18, 2019 8:02 pm

Hello,

When the packs are off for engine start, are the recirculating fans recirculating any air through the cabin to provide some amount of airflow?
 
unimproved
Posts: 99
Joined: Sun Jun 22, 2014 7:14 pm

Re: Recirc Fans/ engine start

Thu Jul 18, 2019 8:46 pm

Depends on of they're switched on or not. Usually leave them off myself but that's without self loading cargo in the back.
 
Waterbomber2
Posts: 383
Joined: Mon Feb 04, 2019 3:44 am

Re: Recirc Fans/ engine start

Thu Jul 18, 2019 8:48 pm

Probably not, but one would have to check the schematics and procedures per aircraft to be sure.
You often hear the cabin ventilation go silent before engine start so that would suggest that they are off.
 
CATIIIevery5yrs
Posts: 116
Joined: Wed Jun 29, 2016 4:40 am

Re: Recirc Fans/ engine start

Thu Jul 18, 2019 9:31 pm

Can only speak for the A320 series at my property, but per procedure, we never turn off the ‘cabin fans.’
 
Lpbri
Posts: 172
Joined: Tue Sep 27, 2016 7:18 pm

Re: Recirc Fans/ engine start

Thu Jul 18, 2019 11:18 pm

Just checked my 787 training manual. Both upper and lower recirculating fans decrease fan speed during main engine start. On a pneumatic airplane, pneumatic loads are separate from electric loads
 
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fr8mech
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Re: Recirc Fans/ engine start

Thu Jul 18, 2019 11:49 pm

A quick look at our schematic manuals shows that there is no fan inhibit during engine start (B744, -8, B757/767). I couldn't find it in the engine start procedures for the flight crew, either.
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DiamondFlyer
Posts: 3099
Joined: Wed Oct 29, 2008 11:50 pm

Re: Recirc Fans/ engine start

Fri Jul 19, 2019 1:01 am

Some aircraft don't even have recirc fans.
From my cold, dead hands
 
Redbellyguppy
Posts: 203
Joined: Sat Apr 01, 2017 3:57 am

Re: Recirc Fans/ engine start

Fri Jul 19, 2019 6:10 am

They run on a 737.
 
masi1157
Posts: 395
Joined: Sun Feb 06, 2011 11:56 am

Re: Recirc Fans/ engine start

Sun Jul 21, 2019 10:20 am

Waterbomber2 wrote:
You often hear the cabin ventilation go silent before engine start so that would suggest that they are off.

That doesn't mean the cabin fans are off. Turning off the packs would leave the cabin fans blowing 1/2 of the air into the cabin, which would reduce the flow noise by (theoretically) 18dB. And that is in fast "silent". On all the (Airbus) A/C I know the cabin fans would continue running (if they were switched on before) during main engine start.


Gruß, masi1157
508 different segments on 100 airlines to 210 airports in 55 countries
 
AA737-823
Posts: 5435
Joined: Wed Mar 01, 2000 11:10 am

Re: Recirc Fans/ engine start

Wed Jul 24, 2019 9:57 am

Contrary to a post above, but on the 737 I've actually heard them "load shed" during engine start, and spool back up after starter switch cutout.
I don't have a wiring diagram in front of me, but I've heard it enough times that it has caught my attention.
Maybe it varies by operator/build spec... like practically everything else on a Boeing.
The dang thing consumes 7 amps in it's low speed setting, and a 737-800/900 would have two of them...

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