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Turbo Fan for air cooling

Printed From: ATR Discussion Forums
Category: ATR Discussion Forums
Forum Name: Pilot to Pilot - Flying the ATR
Forum Description: Discuss proper flying procedures and systems management.
Printed Date: August-23-2019 at 10:02am
Software Version: Web Wiz Forums 11.10 -

Topic: Turbo Fan for air cooling
Posted By: Gattaca
Subject: Turbo Fan for air cooling
Date Posted: January-28-2018 at 7:48pm
Hi, I am hoping to have this question answered. The FCOM states that, “In case of ENGINE OIL LOW PRESS, the turbo fan starts on the opposite side and is running as long as IAS is below 150 knots.”

Does anyone know why turbo fan engages on when engine oil low ptessure occurs?

Thanks in advance!

Posted By: EndangeredKiwi
Date Posted: May-13-2018 at 5:37pm

Do you have an FCOM page reference please?

Posted By: EndangeredKiwi
Date Posted: May-13-2018 at 6:05pm
Found the reference.

The 'eng oil low pressure' is simply a signal for the logic to determine that an engine isn't running. So, if an engine fails, the low oil pressure signal is energised, and that signal runs off to a multitude of systems.

One of those systems, is the air-conditioning. It commands the turbofan on the opposite side of the failure to run below 150kts in broader conditions (ie, irrespective of landing gear position). I can only surmise that this is to assist in cooling of the 1 remaining air conditioning pack. On the ATR, if you lose an engine, you lose the respective air-conditioning pack too, as there's no way to cross-feed to the opposite side while you're in the air.

Hope this helps.

Posted By: Gattaca
Date Posted: May-13-2018 at 7:54pm
Hi! Thank you so much for your reply on this. Yes, I agree that most likely the turbo fan activates to help further cool down the system on the live engine when you get a single engine situation. I didn't think about this until you brought it up, so thanks for that.

Here is another question for you if you don't mind.

When reading the FCOM about the conditions for the aux blue hydraulic pump automatic activation, is states:

- ACW Blue Pump pressure below 1500 psi
- At least one engine running
- Propeller brake released
- Gear handle selected DOWN

(FCOM Hydraulic System general section, 1.12.10)

I understand the Aux Blue hydraulic is there to back up the ACW blue pump in case it fails, but I don't quite understand why the prop brake must be released and the gear handle position must be Down. Can you share your thoughts on this?

Posted By: EndangeredKiwi
Date Posted: May-13-2018 at 10:15pm

My understanding is this:

There are 2 separate scenarios that these criteria cover, on the ground, and in the air.

-On the ground: I think it's so the prop brake can be engaged once the engines are feathered, and to prevent unnecessary running of the pump afterwards.

More detail: when the aircraft arrives on the gate, both propellers are feathered, this has the effect of losing ACW power, and therefore both main hydraulic pumps. According to the 4 criteria from the FCOM, this would then trigger the Aux pump to run, allowing the prop brake to then be engaged when selected (you need blue system pressure to engage the Prop Brake). Once it is engaged, there's no need for the Aux pump to run continuously and needlessly, so, the system logic shuts it off. (As a side note, prior to releasing the prop brake before start/taxi etc, the aux pump button on the centre pedestal must be pushed).

Another additional reason, could be that when you're about to start, and you release the prop brake, the Aux pump automatically kicks in (as per the 4 criteria), thus you have Blue pressure, so it charges your brake accumulator, and your emergency brakes are available if you happened to need them. (Once the condition levers are in "Auto" the ACW will then power the main pumps.)

The reason the "at least 1 eng running" is there, is otherwise, if the plane was shutdown just sitting there and the prop brake was off for some reason, there's nothing else to stop the Aux pump running constantly, as it runs off the hot battery bus, and the other 3 criteria are already met.

-In the Air: (The Prop Brake criteria is irrelevant here, for obvious reasons). If you lose BOTH main hyd pumps in the air, you lose everything: landing gear, flaps, spoilers, nose wheel steering, normal and emergency brakes. You can safely fly without any of those things (no spoilers just mean it's a bit sluggish in turns), so again, there's no point in the Aux pump running continuously and needlessly. But once you come in for landing, you're definitely going to need flaps, plus emergency brakes which you'll need to stop (Normal brakes are gone), and it's nice to have nose wheel steering once on the ground. So, the trigger point to allow these systems to be powered, is selecting the landing gear lever down. This then tells the logic that you're about to land, and allows the Aux pump to run, and power those necessary systems.

Note: Part of the manual gear extension procedure is to select the gear handle down. The sole purpose of that, is so that the Aux pump runs.

I realise that's lots of info.... but hope you can pick your way through it.


Posted By: Gattaca
Date Posted: May-13-2018 at 10:34pm
Hi,Wow! First off, thank you so much for taking the time to explain. I am going have to read a few more times, and think it through with my diagrams and schematics on the FCOM to understand it all. Pretty amazing that you can see the systems so clearly. I am ashamed to say I am still in the process of learning this plane.

Do you fly the 500 in New Zealand? I got a Japanese F/O buddy that used to fly ATRs in NZ until recently. He is in Macau now flying the Airbus. Anyhow, thank you again and happy flying.

Posted By: EndangeredKiwi
Date Posted: May-13-2018 at 10:38pm
No worries, it's a good refresher for myself! Lol...

Yup that's right, it's a fun place to fly.

Any other questions, feel free to ask.


Posted By: Gattaca
Date Posted: May-13-2018 at 10:41pm
Yep, my main motivation to study these days is my six month recurrent sim haha. I better hit the books/ipad a little more frequently than that lol. Turn over a new leaf, so to speak.

I will be sure to let you know if I run into more ATR mysteries! Thanks a bunch!

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