737 Pressurisation

[@tonylayfield8750]

One trusts that Chris won't mind me adding a gem of wisdom? If a pack or bleed fails at cruise altitude the aircraft 'should' hold the cabin pressure on one pack / bleed, at least that's the theory. The reality however can be very different and you might well find that, on one pack / bleed, the cabin starts climbing up to meet you... and therein you don't have long to address the problem before the cabin altitude hits 10,000ft (beep beep beep in the flight deck) and continues to climb (masks drop in the cabin and then you're probably diverting for a problem that could have been averted). So, having had a failure of a single pack / bleed you decide to descend (e.g. down to FL250 or below). It's not (yet) an emergency, so you ask ATC for a descent clearance. They of course ask "Is all ok ?" to which you reply, in your smoothest airline pilot voice, that it's just a minor technical problem and that you're descending purely as a precaution. They clear you to descend... you set the MCP altitude and dial-in some V/S... let's say 1,000 fpm (there's no point alarming the Cabin Crew and pax with a heroic emergency descent, is there?) The thrust levers retard a bit (based upon whatever V/S it is that you've dialled in) and down you go... marvellous. Unfortunately, retarding the thrust also causes the pressure in the duct to drop and now the cabin altitude (being contained by just a single pack / bleed) starts climbing up to meet you with a vengeance. Doh! However, being a consummate professional, you've anticipated this and have spotted it on the overhead panel. So, what to do ? You might choose to increase the rate of descent, which in turn will retard the thrust even further, therein reducing bleed pressure even more, thus exaserbating the problem. It then becomes a race of which will occur first, i.e. will you get to your level off altitude (when thrust is reapplied and the duct pressure comes back up again) before the cabin altitude hits the limits for masks dropping and whatnot. Uhm! OR Initiate an emergency descent (uhm, might seem a bit excessive for what should be a controllable problem). OR Maybe what you could do is increase the thrust (which seems counterintuitive wrt descending) - if needs be, just applying thrust on the engine that's driving the operative pack / bleed - which thereby re-pressures the duct to an extent that the cabin stops climbing (or at least climbs more slowly)... and thereafter do whatever needs to be done to control the effect of the additional thrust upon ones airspeed and / or to control the rate of descent and / or deal with any thrust asymmetry, during the descent. In any event, with a single pack / bleed failure at cruise altitude, when you close the thrust (even partially) to descend from cruise altitude, keep a very beady eye on that cabin altitude. Fwiw, the above has happened to me (more than once) on B737 and B757.

[@ChrisBrady737]

Hi Tony, I absolutely do not mind hearing your wisdom. One should always embrace the experience and learnings of others as it may save you from having to go through the same yourself. Absolutely top tips and a great idea about maintaining the onside bleed pressure. Chris

[@GNX157]

So would deploying the speed brake (keeping your hand on the lever of course) during the descent while keeping a steady thrust work?

[@tonylayfield8750]

@@GNX157 in a word ‘yes’… it’s worked for me (more than once)… though it’s a case of using one’s judgment as to which is the best course of action for the specific problem that one’s facing. You need to get the aircraft descending as fast as you can, but (in the scenario I’ve described above) you’re doing so with power still applied (on one engine at least, if only to keep pressure in the bleed air duct on that side to, hopefully, arrest the rate at which the cabin altitude is climbing and, hopefully, therein avoid having the rubber jungle deploy within the cabin). The alternative is to close both thrust levers (which will cause the bleed air pressure to drop to bugger all, following which the cabin altitude will undoubtedly start climbing), pull the speed brake to the flight detent, and hope that you can descend fast enough before the cabin altitude climbs to 14k ft and the rubber jungle deploys.

[@tredi7655]

Dear Chris, these presentations are, by far, the best i could find on youtube. They are a great (and somehow necessary) complement to the manufacturer flight manuals and CBT learning aids. Many thanks for sharing your knowledge with visuals of systems and insight that cannot be found if studying only on manuals. Please keep going!

[@ChrisBrady737]

My pleasure, thank you for your kind comments

[@OsagieFrankIgbinovia]

Its not everyday you see an aviator sharing knowledge gained throughout the years. As easy as it is to access the video on you tube i am sure it took years of learning, preparation and planning. The whole aviation community salutes you for making the skies a more safer place by sharing your technical knowledge.

[@ChrisBrady737]

Hi Osagie, Thank you very much for your kind comments about my videos. It did indeed take many years to build up my knowledge and experience to the level shown in the videos. I was happy to make them and give them back to the community which has given me such a great career.

[@richard_muschette3009]

Thanks so very much for this presentation Chris, its very meticulous and articulate, you have covered so many imperative points in this short presentation, it helps me to understand things much better on my job and as well explaining to others how the system works.

[@ChrisBrady737]

Thank you for your kind comments, you are very welcome.

[@richard_muschette3009]

Hey Chris please let me know how and where l can purchase copies of your book....

[@ChrisBrady737]

Hi Richard, if you follow this link you can find ways to get the book in either printed, EPUB or even Chinese editions! www.b737.org.uk/book.htm

[@scubastevewa8580]

Incredible presentations. I'm not pilot, just someone with a passion for aviation and enjoying this information none the less. Much of this is applicable to the desktop sims I use as well, it's amazing how advanced they are now.

[@ChrisBrady737]

Great to hear - enjoy!

[@akashoa7929]

I m flying the 737 since ages and i thought ,as B737 TRI , i know everything until i have seen Capt Chris web site . Thanks Chris

[@ChrisBrady737]

My pleasure, glad you are enjoying them.

[@telescope64]

Thanks Chris. Once again a great system overview.I like the description of the evolution of the system over the decades and the various options.Some great tips in there,good work. Best wishes from Paul.

[@ChrisBrady737]

Thanks again Paul

[@captaincrypto8244]

Love the videos here! Thank you very much, helping me to refresh my knowledge as Im going back to the 737 after six years of long haul.

[@ChrisBrady737]

My pleasure, glad to help. You should check out my book, the electronic version is on at half price from Apple Books for another week.

[@matthieulambinet9522]

Everything we always dream came true with these videos series. Thanks a lot.

[@ChrisBrady737]

My pleasure, and lots more videos to come.

[@tindlesteve]

Big thanks for this presentation. Very informative.

[@ChrisBrady737]

My pleasure

[@pranavchhabria2479]

Excellent videos, really appreciate the hard work. Thank you and kind regards!

[@ChrisBrady737]

Many thanks, glad you enjoyed them.

[@neekoweeclearwater2305]

Another greatly appreciated video. Very informative and easy to follow

[@ChrisBrady737]

You are welcome, thanks for watching.

[@fkatircioglu]

I really like your videos. Please keep this going. Thank you.

[@ChrisBrady737]

My pleasure, many more to follow

[@mattiassjogren2840]

Excellent videos, thank you for the hard work! Kind regards

[@ChrisBrady737]

Glad you like them!

[@alexleao1159]

Great presentation, thank you for your time.

[@ChrisBrady737]

My pleasure Alex. Stay tuned for the next videos

[@bonk945]

Appreciate the video and the work done. Thanks!

[@ChrisBrady737]

My pleasure, glad you found it useful

[@YonderPiLoT]

So I really enjoy the educational dept of your videos. Thanks for sharing. I was listening to this episode while driving and got caught up deeply. Think about the feeling I had when I suddenly heard the cabin alt warn horn and started to question life😅😅

[@ChrisBrady737]

That’s great to hear, glad you are enjoying them.

[@spiritzm]

Thanks a lot, Chris! Nice explanation!

[@ChrisBrady737]

Thanks for the feedback, glad it was helpful.

[@harisshahulhameed5966]

Very good video. So much information. Thanks for the video.

[@ChrisBrady737]

My pleasure.

[@Wealthsimpletrade]

This is great keep it up!!

[@ChrisBrady737]

You are very welcome. Please tell your colleagues

[@ppauloreis]

Thanks again Captain!

[@ChrisBrady737]

You are very welcome

[@T0MaTOS]

Thanks again Chris for the excellent presentation!

[@ChrisBrady737]

My pleasure, glad you found it useful.

[@T0MaTOS]

@@ChrisBrady737 Hey Chris? Your knowledge of the 737 is amazing, and you are a godsend for pilots like me...THANK YOU for sharing Chris! I just watched your ANTI-ICE video and learned what the different types of icing on the 737 were, and what to look for. I must say that we hardly see any of the moderate to severe icing here in Hawaii, but I did see SEVERE icing like what you described in the video. Now, I know! Do you advise turning on the WING ANTI-ICE during moderate icing? Thanks again, Chris!

[@ChrisBrady737]

Hi Jay, there is a section in the FCOM Supplementary Procedures - Adverse Weather called "Wing Anti-ice Operation In-Flight". It states that wing anti-ice can be used "as an anti-icer only during extended operations in moderate or severe icing conditions, such as holding.". Elsewhere in the SP it tells you to avoid moderate to severe icing conditions.

[@T0MaTOS]

@@ChrisBrady737 Thanks again, Chris! I did see you relay that in the video.

[@hamzafox863]

Thank you Captain Brady, once again, amazing work. Do you plan on making a presentation on the Autoflight system eventually? You have a great way of boiling complicated things down to the point. It would be extremely helpful to me for my upcoming simulator training.

[@ChrisBrady737]

Thank you for your comments. Autoflight is on the list but wont be happening anytime soon as I am busy flying in summer.

[@hamzafox863]

@@ChrisBrady737 That’s okay, I’m sure whenever it comes out it will still be helpful with whatever phase I’m in at the time. Fly safe Sir.

[@caleb0606]

These videos are so helpful and great

[@ChrisBrady737]

That is good to hear, thank you. Please check out my other videos and tell your colleagues

[@caleb0606]

@@ChrisBrady737 I am just a young aviation enthusiast learning about the 737

[@ChrisBrady737]

I and most pilots all started out the same way. Study hard and there is no reason why you should not be able to become a pilot yourself. Good luck

[@caleb0606]

@@ChrisBrady737 thank you.

[@inusaibrahimg.5355]

Thank so Much Cpt

[@ChrisBrady737]

My pleasure

[@MrEkg98]

I wish I had a good way to contact you to ask obscure questions. I have 18 years on the type as a AMT. You mentioned blow out panels. I never knew how important these were. After the DC10 incidents I understand better. I remember being very new mech and seeing guys just go nuts with the cargo pit tape. I remember seeing the tape used on blowout panels. I also then shortly there after remember people getting yelled at for doing it and made to take it off.

[@ChrisBrady737]

Unfortunately I am too busy to take individual questions but you could ask on The 737 Technical Group, there are a lot of very knowledgeable pilots and engineers on there. facebook.com/groups/737tech

[@alkitanishihab]

i'm impressed how come a pilot knows all those information .. you know more than engineers lol

[@ChrisBrady737]

Thank you, I have been flying the 737 for many years and learned a lot from engineers along the way.

[@alkitanishihab]

you are the best pilot I ever seen . I loved your channel and I will share it to all my friends .

[@atiyos]

thank you

[@ChrisBrady737]

You're welcome

[@leg01]

Hi Chris, it may be worth mentioning that there is no mechanical stop on the cabin altitude indicator at zero ft. Apparently there was an incident in 2018 where a crew had a CPC2 failure in the CRZ, carried out an emergency descent and correctly closed the OFV i.a.w. with the memory items. On descent the cabin differential pressure reached 8.75psi (PRV helped to maintain this), and the cabin altitude which was at 15,000 ft at the time of the failure, reached -7000 ft. However, interestingly this was displayed as +33,000ft on the indicator as there is no mechanical stop (i.e. the pointer went through zero ft.). After some confusion (naturally..) the crew opened the OFV before commencing the approach and the differential pressure normalised. It would have been a very confusing picture to have seen +33,000 ft cabin altitude and +8.75psi diff. at 9000 ft aircraft barometric altitude. Maybe worth a mention in your future presentations as a bit of additional info. Refer to Interim Report BFU18-0975-EX. Interesting!

[@ChrisBrady737]

There have been many variations of this type of incident over the years, many with some mishandling of the DCPCS panel. The BFU report states that the panel can be confusing. Details on my website here www.b737.org.uk/incident_ei-enm.htm

[@leg01]

@@ChrisBrady737 Thanks as always Chris. Yes I see the crew had a bias due to the way operators usually train for this scenario in the sim (with damage and uncontrollable cabin alt.). Really good that you mentioned it on your brief analysis found on the link above - great lesson/reminder for all B737 flight crew.

[@lihenry4404]

Thanks Chris！ This video helps me a lot about pressurization system. Why does our company only mention the schedule below 28000ft on FCOM Δ P is 7.45. The number 18500ft is not mentioned. Was it written on your FCOM or learned by the maintenance manual？

[@ChrisBrady737]

Good spot, I had not noticed that they had removed the 18,500ft reference from the FCOMs - but it is absolutely true for all generations of 737 and it is still documented in the AMM. It is probably an oversight on Boeings part to remove it in the process of simplification for pilots. They don't want to bother us with such info!

[@MatthijsvanDuin]

19:30 I would believe that without even a moment of hesitation, in fact I would have been flabbergasted if it were _not_ integral to a panel designed in the last two decades. A robust, reliable connector that can accommodate the many signals needed to externally drive the individual elements of the panel would probably take _more_ space than a microcontroller driving them locally.

[@ChrisBrady737]

👍

[@fromdreamtotakeoff1786]

Thnk you so much for this video but barely hear you with full volume on ipad. Thank you , Captain .

[@ChrisBrady737]

HI, so glad you liked it. I know the first few videos were quiet but I thought I had fixed it in the last few videos. Are you sure it was this one that was quiet?

[@zlatimirzdravkov8940]

Thanks

[@ChrisBrady737]

You are welcome

[@iandudman9529]

Another great lesson please keep it I’m learning so much.

[@ChrisBrady737]

That's the plan!

[@treborg777]

How does one leak-test the fuselage to find pressure leaks? I’ve done a lot of high vacuum system leak testing, I’m curious how Alaska could have pinpointed the plug door leak.

[@sinancoskun8638]

Hi Captain! Thank you for the channel. Are there any cabin pressurisation difference between a320-b737?

[@ChrisBrady737]

The systems are very similar

[@rjmunro]

In the recent Alaska Airlines door failure incident, Jennifer Homendy of NTSB said pilots reported "pressurisation warning lights" on three previous flights made by the specific Alaska Airlines Max 9 involved. She didn't mention the altitude warning horn. I wonder if this was the "Auto fail" light (at 10:47), and if that failed would it be normal to allow a plane to continue flying until the pressurisation controller can be fixed?

[@ChrisBrady737]

Yes it is "normal to allow a plane to continue flying until the pressurisation controller can be fixed". There are approved procedures for this in the MEL.

[@ke282]

Hi Chris, I am currently doing research regarding the Boeing 737-800 aircraft ceiling, I could only find the service ceiling (41,000 ft) but could not find any sources that state the absolute ceiling of the Boeing 737-800. May I know what is the absolute ceiling of that aircraft? Greatly appreciate it. Thank you.

[@ChrisBrady737]

The maximum certified ceiling is 41,000ft. The actual physical ceiling will depend upon weight, ISA deviation, CofG, buffet margins etc

[@DavidJohnson-yy4de]

Hey, Chris. Does the outflow valve open or close during a climb to slowly increase the cabin altitude? I've been told that the outflow valve slowly opens after t/o to increase cabin altitude but I'm not sure about that

[@ChrisBrady737]

It normally closes as the aircraft climbs

[@despoticmusic]

When on ground, the outflow valve is driven to the full (AUTO) open position. With the doors open and the packs OFF, the cabin pressure will be ambient. With the doors closed and the packs OFF, the cabin pressure will be ambient. With the doors closed, and the packs moved to AUTO, the vast majority of the pack air will pass through the OFV, but the OFV doesn’t have sufficient outflow area to give a delta pressure of exactly zero - I think Boeing specs say less than 0.06 psid? My question is - how does this small build up of delta pressure manifest at the Rate of Climb indicator when the packs are turned on? Is it noticeable or not? Has anyone done this in a 737?

[@ChrisBrady737]

Yes, switching packs on and off on the ground with doors closed will give a kick on the cabin VSi, just as flushing the toilet or even emptying the sink will do the same in-flight!

[@despoticmusic]

@@ChrisBrady737 Thank you. Do you have any idea of the RoC indicated during a typical packs on “kick” whilst on ground? It seems such a small dP, and I’m surprised the lagged gauge/sensor picks it up!

[@ChrisBrady737]

@despoticmusic It is just a brief kick. If you could read the gauge it wouldn’t be accurate as it is so transient.

[@Nav2041]

Can you clarify your comment you actually descent so fast as to catch the cabin ,that exceeds the automatic pressurisation system

[@ChrisBrady737]

Catching the cabin is where you descend so quickly that scheduled cabin RoD is insufficient to depressurise the cabin in the time you give it.

[@Nav2041]

Thank you fir your kind reply appreciate it captain sir

[@spiritzm]

+1