Someone can Brief about the Recirculation Fans in 737 NG, about their position at the different stages of the flight?About what i found we shoud use them on when the packs are off, is this correct?

Recirc fans should just be left on, unless it's necessary to turn them off, from what I understand.Recirc fans are there to circulate the air around the cabin, so it's best to leave them on so that the air doesn't become "stale." I believe the QRH has some references to turning it off in the event of smoke or some other air contaminant in the cabin.I'm sure someone else has a more exact definition and procedure though.

Yes but you see alot of real 737's videos and they have the rec fan off, and at smart cockpit web site i saw some refference about have the rec fan on only when one or both packs are off, but without 100% sure

As Kyle says, recirc fans are usually on unless they need to be off due to e.g. smoke. You might switch them off on the ground when the aircraft is empty though.Best regards,Robin.

The second recirc (on the right in the 800) is quite loud on the flightdeck. It is often turned off, for this reason.* Orest

Recirc fans are intended to boost ventilation when there is low airflow from the packs. According to the FCOM, in the Auto position they will run unless both packs are operating and at least one is in full flow.

I leave them off.. sounds like someone fires up a jetengine inside the cockpit :(

Like Kevinh said when both pack are on rec maybe can be turned off due the noise but once again without 100% sure xD

Recircs are off for ground cooling with external air, too. There's no point in recirculating the pre-conditioned air if you can just pump more in.

One reason to use the recirc fans it to save fuel. They recirculate the old cabin air causing less demad for new air from the packs which get their from the engines. When the packs take air from the engines they take power away from them so the engines have to work a little harder to get a given amount of thrust. I have never seen a number publshed as to how much of a fuel savings it really makes though. The 787 has no engine bleed air so it won't be a problem on that.The main reason to turn the recircs off on the ground, mainly on hot days, is because the air flows down around to forward cargo compartment on its way back to the mix manifold. On a hot summer day that air is heated when it does this so if the recircs are on you are just pumping warm air back into the plane counteracting the pre conditioned air. Turning them off really does make a noticable difference in the cabin but it could just be my perception but the cockpit feels a lot hotter to me.

I leave them off.. sounds like someone fires up a jetengine inside the cockpit :(

I agree the NGX fans are pretty noisy. Are they this loud in RL? If leaving them on is SOP, can their volume be lowered a bit in the next SP?Thanks.

I agree the NGX fans are pretty noisy. Are they this loud in RL? If leaving them on is SOP, can their volume be lowered a bit in the next SP?Thanks.

It seems like in our original batch of 737s we (Aemrican Airlines) received from 1999-2002 they aren't that loud. In the newer ones they really are. I typically turn the left one off until we start the engines. By then we have our headsets on and the noise isn't as noticable.

In the newer ones they really are. I typically turn the left one off until we start the engines. By then we have our headsets on and the noise isn't as noticable.

OK, Tom. Thanks.

Ralgh can you descrive in the different stages of flight how they should be set please?

In flight, take it/them always on AUTO position. AUTO position always means that the system will automatically use or not the recirc fans if required.The logic depends on PACK configuration (OFF AUTO HIGH) and air ground condition.Put to AUTO and forget them.