Too much reliance on QRH?

[The Real Slim Shady]

The NG QRH was probably written by lawyers to cover the product liability problems etc in the US. However, how far do you have to go in following what it decrees?
For example, if you lose the No 1 (left pack ) the QRH calls for the pack to be switched off if it cannot be restored. If you then have a No 2 bleed trip and follow that checklist you find yourself without pressurisation.
Nowhere does it mention the commonsense "open the isolation valve and feed pack 2 from bleed 1 scenario".
OK, so it probably only ever happens in the sim, but, what would you do and why?
Bearing in mind you are now working outside of the protection of the QRH

[Streamline]

As far as I recall: if the isol sw is in auto and you switch of a pack...it will open ..so what is the problem?

[B737MRG]

I must confirm Shady has a point ; the PACK NNC calls for "Isolation Valve Switch.... Close", so you need some common sense to combine the 2 checklists.

There are several cases on the B737 (and on other airplanes certainly too) where the combination of 2 failures and/or NNC requires some self-inventiveness.

[Feather #3]

I'd further suggest that scenarios like this are covered in the Checklist introduction at the front of the QRH.

G'day ;)

[john_tullamarine]

One needs to keep in mind that the basic presumption is a single failure. So QRH/MEL use in the event of multiple failures becomes a tad messy and not the province of those who don't have a very detailed knowledge of both systems and design/operations certification.

[Streamline]

One needs to keep in mind that the basic presumption is a single failure. So QRH/MEL use in the event of multiple failures becomes a tad messy and not the province of those who don't have a very detailed knowledge of both systems and design/operations certification.

Thats a good description of our job.

[john_tullamarine]

Except that, in my experience, pilots sometimes don't have much, if any, knowledge of system failure analysis, FMECA, and certification standards, generally.

Hence, I might be of the view that routine line use of QRH/MEL is fine for single failures but fraught with problems with multiple failures. This might especially be so where crew knowledge is limited ... not saying that this applies universally .. but certainly one cannot presume that crews have an appropriate level of knowledge .. and "appropriate" goes far beyond a typical pilot engineering endorsement and simulator training.

[Centaurus]

It comes as no great surprise to some that many pilots have no interest in the contents of the checklists (non-normals) in the QRH unless Recall items are called for. They work on the perceived basis that the QRH will lead you to the truth step by step so why bother. By the way, anyone know of items missed in day to day operations using the new Boeing scans and the shortened normal checklists?

[RMC]

I am a professional pilot and do have training in Failure Modes Effects and Criticality Analysis (FMECA), Certification standards systems failure analysis. I have had to deal with specialist designers who have had more knowledge in their little fingernails than I have in my being on their particular area of expertise (even though I am one of the most highly qualified engineering pilots in the UK).
What some of my colleagues do not realise is that the crew manuals they read are.
1. Written by generic technical authors with little specific systems knowledge (in comparison to their specialist design colleagues).
2. Are, in any case, the "Ladybird book" of aircraft systems (a typical airline 2Systems Description Note for Chapter 28 (Fuel) will take up a couple of metres of shelf space in A4 format). My pilots tech manual (fuel section) has around 0.25% as many words and pictures as the designers reference manuals.
3. As well as being simplified there are often errors in the diagrams and text of our Tech manual "bible".
If anyone wants to kid themselves that they understand the complex interactions in a multiple failure case (especially management fleet managers) then I hope you never have to defend your position in court. Yes there are circumstances where we might have to make a judgement call (where the QRH leaves you stranded) but that is the only time you should ever go outside the designers instructions. QRHs are rigorously checked by experienced design specialists (lip service is often paid to pilots tech manuals).:sad:

[Piltdown Man]

I must be the luck one! The checklists (Normal, Quick, Emergency and Abnormal) have covered virually every failure I've encountered over the past 12 years. I fly Fokkers and by comparisson with the 737 very young. The only time I've had to work outside the checklist was when an AHRS unit "half" packed up.

[Streamline]

Except that, in my experience, pilots sometimes don't have much, if any, knowledge of system failure analysis, FMECA, and certification standards, generally.
Hence, I might be of the view that routine line use of QRH/MEL is fine for single failures but fraught with problems with multiple failures. This might especially be so where crew knowledge is limited ... not saying that this applies universally .. but certainly one cannot presume that crews have an appropriate level of knowledge .. and "appropriate" goes far beyond a typical pilot engineering endorsement and simulator training.

QRH is just a tool at the disposition of the crew. As such it's only a part of the decision making process and not the process itself.

Access to the profession is far too easy.

[alexban]

actually ,B737MRG, pack trip off NNC, has no mention of isolation valve....what QRH are you using?
only temp select to warmer,and trip reset switch push.....
The pack should not be selected off.....it is closed automatically due to temperature exceeding limits.No mention for pack selected off.
It's the same for classics or NG.
I wonder what qrh are you using guys?
Now,for a bleed trip off,after pushing the reset switch,with no effect,you should select the affected pack to off.
You'll say now,what if the other pack fails?....what if?....
You should read page CI.2.4.....it's in all types of planes I know off:
'pilots must be aware that checklists cannot be created for all conceivable situations and are not intended to replace good judgement.In some conditions ,deviations from check;lists may,at captain discretion,be needed.'

So,select second pack off,first bleed off,first pack on....work for you?
Or,if you want to do it by the book,follow the both pack trip off light..no pack available....(if you doesn't feel too safe on your knowledge about the aircraft)
Brgds

[I-2021]

Hi alexban,

just a little question to see if what I am thinking is completely out of the line:p Imagine the aircraft dispatched with, let's say, Left Pack Inop. The MEL/DDPG ask you to select the affected pack "OFF" and Isolation Valve switch "CLOSE". After takeoff you have a right bleed trip off. You end up to a point where you have to close the pack switch on the right side. Before doing that, can you just open the isolation valve (or select it auto) and leaving the right pack AUTO ? You will be feeding the right pack with left bleed air. Is that the way you could manage such a situation ?

[The Real Slim Shady]

737 - 800 QRH
Condition: A PACK light illuminated indicates both primary and
standby pack controls have failed or the related pack
valve is closed due to temperature exceeding limits.
ALL TEMPERATURE
SELECTORS . . . . . . . . . . . . . . . . . . WARMER TEMPERATURE
[Reduces the work load on the affected air conditioning pack.]
TRIP RESET switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PUSH
[If the PACK light illuminated as a result of the pack temperature
exceeding limits, the light extinguishes if the pack temperature has cooled
below limits.]
If one PACK light remains illuminated:
ISOLATION VALVE switch . . . . . . . . . . . . . . . . . . . . CLOSE
PACK switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .OFF
Alexban
Being a clever dick has no place in a rational discussion between professionals when advice and considered opinion is being sought.
If you don't feel able to add something of value to the discussion please don't involve yourself.
Guys and Gals,
Thanks for the replies. I agree with JT that the QRH doesn't deal with multiple failures and the rider that the Commander can take whatever actions he / she deems necessary for the safety of the flight, however, with a new generation of pilots coming through who have little, if any experience of non - automated flight decks, is there a danger that too much reliance is being placed on the QRH now?

Bear in mind the implications of not following a QRH procedure, or varying it, if the issue comes to court.

[I-2021]

Mmh, maybe you are talking about 2 different NNC. the "PACK" NNC (-400) asks for ISOLATION VALVE SWITCH CLOSE. The "PACK TRIP OFF" NNC (-300) does NOT ask for ISOLATION VALVE switch to be placed CLOSE.

[alexban]

Real Slim...the NNc you're talking about it's specific for the 400/800 series...so ,if 'you don't feel able to add something....".quite a professional remark from your part..:cool:
But ,maybe ,you flew only 800 series,so it's ok ,then....it is a bit different from other 737 series,you should know..
Did you read my entire post,or you just stopped after the first phrase...deeply offended,i guess..:rolleyes:
I-2021 ...departing under MEL on such a case will restrict you to FL 250 ,if I remember correctly.This is exactly for a malfunction like the one you've imagined.In such a case,I guess,I'll use a 'crossfeed' for the remaining pack.
And if this is not working,i'll follow the 'both pack trip off light' nnc..

[I-2021]

Real Slim...the NNc you're talking about it's specific for the 400/800 series...so ,if 'you don't feel able to add something....".quite a professional remark from your part..:cool:
But ,maybe ,you flew only 800 series,so it's ok ,then....it is a bit different from other 737 series,you should know..
Did you read my entire post,or you just stopped after the first phrase...deeply offended,i guess..:rolleyes:
I-2021 ...departing under MEL on such a case will restrict you to FL 250 ,if I remember correctly.This is exactly for a malfunction like the one you've imagined.In such a case,I guess,I'll use a 'crossfeed' for the remaining pack.
And if this is not working,i'll follow the 'both pack trip off light' nnc..

thanks alex, that's what I was also thinking.