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B777 HYD R+C NNC

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B777 HYD R+C NNC

Old 29th Sep 2021, 04:02
  #1 (permalink)  
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Join Date: Feb 2021
Location: Taipei
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B777 HYD R+C NNC

Hello everyone,

I have a question regarding which checklist to use first when HYD R+C has a leak and all the quantity is gone.

Supposedly there will be a lot of EICAS msgs but the two we are most concerned with is HYD QTY LOW R+C and HYD PRESS SYS R+C

When reading their objectives is seems that we should be doing HYD QTY LOW R+C checklist first since HYD PRESS SYS R+C is basically a consequential checklist of HYD QTY LOW R+C (even though it kind of doesn’t fit the description by BOEING QRH , that is “If a consequential checklist has steps, notes, and information that are needed for the primary failure condition, then these are included in the primary checklist.”).

I recently had this NNC(HYD R+C fluid loss) on a check and the check airman was adamant that we do the HYD QTY LOW R+C first since this checklist tells us to close C1 ELEC PRIMARY pump switch to OFF, in order “To prevent fluid loss through the brake system.”

But the system description from FCOM2 states that “If center hydraulic system quantity is sensed to be low and airspeed is greater than 60 knots the alternate brakes are isolated from the center system and remain operable using reserve fluid.”

So I guess what I am asking is how would the fluid be loss through the brake system? And if it is so critical why isn’t it (turning C1 ELEC PRIMARY pump switch OFF) in the HYD PRESS SYS R+C NNC? (Well I think it’s not there because you might just have some pump faults but quantity is okay, but I would assume if it was very critical there would be a conditional line item in the NNC, i.e IF HYD QTY LOW R+C msg shows, C1 ELEC PRIMARY pump switch OFF etc.)

In a sense the aircraft already did this for us, I feel like you would always do the HYD PRESS checklist first.

Any thoughts or any system knowledge I am missing here? Or should we always do the HYD QTY LOW NNC before HYD PRESS SYS first as they will always come hand in hand when hydraulic quantity is low?

Thanks in advance!
Kevingee21 is offline  
Old 2nd Oct 2021, 21:36
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Join Date: Jan 2005
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I would say that you are correct. For low Quantity, it may be possible to preserve some quantity to enable use the brakes.

Once the system has low Pressure (from loss of quantity), this is no longer possible:
Normal brakes and alternate brakes from center hydraulic source are inop
Alternate brakes from the reserve hydraulic source are available.
It's been a while since I looked at this scenario, but with low Pressure being consequential, if you hadn’t already started the low Quantity checklist, it is not required.

Since this was presumably in a Sim, you will already know who is “correct”.

Good luck.

Last edited by awair; 3rd Oct 2021 at 02:37.
awair is offline  

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