It’s 1:30 AM. I have no interest in becoming a pilot or an airplane mechanic, and I rarely even fly, yet here I am watching an hour long video on the APU for the 737. Great video, if you made it accessible to some random guy, they you definitely made it accessible for your audience.
That is incredible, thanks for your feedback. BTW I admire your concentration levels to be able to watch a technical video at that time in the morning, or were you just looking for a way to fall asleep!
@@ChrisBrady737 I had one of those youtube shorts pop up, and it was filmed inside the tail section of a 737. There's a guy that draws parallels between aircraft mechanics and Lord of the Rings lore... It's... Interesting. It got me curious about what was in there (the tail section of a 737, not Middle-Earth), so I searched and found your video. I find aircraft fascinating, as they are mass produced but the relative quantities are still so low that they're built like an engineering prototype. Boeing has made 11,550 737s in 55 years. In 2022, Apple produced 11,550 iPhones in 26.9 minutes. Learning about how airplanes work is fascinating enough to keep me from going to bed at a reasonable time!
Absolutely fantastic series. I have been a Boeing (737-747-747400) IP since 1978 and NOTHING even remotely compares. Thank you so much! If you really want to know your Boeing 737 from either a pilot's or a mechanic / ground engineer's desire for excellently presented information. 😁
Hello Chris, thank you for the excellent information. I am a trainer on the 737 in Canada. Our Max’s do have an optional installed dc fuel pump. My understanding is this is a requirement for the APU on condition ETOPS certification we have. We do not need to run the APU during ETOPS as long as the fleet meets reliability parameters. Thanks!
Thank you so much for posting this information up. I'm guessing this is what the engineers were looking at during a 'quick turnaround' last night in Tenerife when the flight out was delayed with us all watching from the front of the aircraft. For a good hour there was a couple of guys up a ladder, with their heads inside the access panel, with torches, then they were inside the aircraft, then back out, then on the phone etc etc. It certainly didn't settle anyone elses nerves watching from the sidelines. I had to tell my daughter that they wouldn't let the aircraft fly if it wasn't safe to do so. Then when we finally were allowed on board, the cabin crew wouldn't give us any sort of details apart from it was a technical issue and they can't fly out until the log has been completed and returned back to the aircraft.
You are absolutely correct, the engineers and pilots would not allow the aircraft to fly until it was safe to do so. Incidentally the APU is not required for flight, its main purpose is to give electrical power and air conditioning on the ground and to start the engines. But airports have ground equipment available to perform these tasks if needed.
Hi Chris, very informative series. I have a question. I have seen for an APU start, that if you first move the switch to the on position for a short period, then move it to the start position, you get a much quicker start. I haven't found an explanation for this anywhere. Do you know why this is? I assume that its bad for the service life of the APU as well? Thanks
Best 737 presentations. I was trying to acquire physical copy of your book on Amazon but I believe it was sold out, will there be more in the future? Thank you as always, Captain. Little by little, day by day, expanding my understanding of this aircraft ✈️
Hi, thank you for your kind comments. The Amazon edition is out of date. The current hard copy edition is only available here: www.blurb.co.uk/b/11658762-the-boeing-737-technical-guide
I have a practical question regarding to bleed pack operation on classic a/c equipped with Garrett 36-280. Do pilots can actually use both packs on the ground with the APU bleed on or is it prohibited by the SOP for commonality reason?
Thank you for this detailed presentation, I have a query, at 10:37 in the slide it’s mentioned that the Honeywell 131-9 is rated for 90kVA for up to 32000ft, but in the slide at 25:01 the table mentioned the 90kVA is provided up to only 31000ft, which of these two figures would be correct, thank you once again.
43:46. That's not a vortex generator, it's an ogee wing which directs air into the scoop. The original NACA scoop (seen) was designed for minimum drag but has no ram recovery--the ogee wing allowed inflight starts. 46:24 It's important to note that earlier 737 APUs were mounted between Critical Structure frames, so temps had to be controlled to avoid damaging the aluminum as well as making its engine bay fireproof by use of a stainless shroud, which limited maintenance access. As with the 757-767, the MAX APU is mounted behind the last structural frame, where the only temp/fire protection needed is a firewall aft of the last frame.
I agree that the vortex generator is the shape of an ogee wing, and I see your point about it directing air into the scoop, however I was just using Boeing terminology. Good info about the mounting between / behind critical structures. There is always something to learn about this aircraft, thank you!
Dear Chris, I ask you the following question: does placing the switch in the ON position start the APU start-up process or does it start it directly when we momentarily place the switch in start? If so, what part of the process starts when you turn the switch on? I have noticed that this way, first on (lets say while we are taxiing) and then start (entering the gate), the start process takes "less time". Thanks in advance.😢
Hi Chris, great explanation videos. Have a question about leading edge devices when Hydraulic system B fails. Basically it says PTU uses system A to pressurise fluid system B to operate auto slats and leading edge devices. But when coming to the alternate operation leading edge operation it says standby hydraulic system operates leading edge devices but standby hydraulic system doesn't retract them back. Basically the doubt is when system B is INOP, can we say that PTU retracts the leading edge devices lets say after a take off and then the sby hydraulic system powers them to the full extend position. Thank you for your answer
This is not an APU question but... For autoslat operation, the PTU will be used to extend and when safe retract the LE slats using Sys A pressure if there is Sys B fluid available.
Hello Chris, i have a question, not related to this video, but for water system of B737NG, do we have compressors for water system pressurization on all B737NG airplanes or they are optional. Secondly your videos are very detailed and informative, thanks a lot for all of your efforts.
There is auto-shutdown logic. If that fails then it will have to be a manual shutdown by the crew. I suspect that if the EGT signal is lost then the ECU will shutdown the APU.
Hi Chris.. I think they have a DC Fuel boost pump for APU in MAX as well. Because I have an MEL for the same and I cross checked it in the MMEL as well. Please guide me if I am finding it at wrong place.. Thanks a lot for your efforts..
My information says that they don't have a DC fuel boost pump - "The center tank boost pumps or the boost pumps in the No. 1 and 2 main tanks supply fuel to the APU. If the main tank boost pumps are off, the APU can suction feed fuel from No. 1 main tank.". It wouldn't be the first time that the MEL was wrong. Or maybe it is an option.
Good Day Capt Brady, for short houl flight within 2 hours do pilot still manual calculated remain fuel every hour to cross check incase of fuel leckage?
Hi Capt, Would be a great idea if there is a Telegram groupchat, so that pilots and aspiring pilots could share their knowledge and latest update on the 737 development. I’ve seen similar groupchat for the A320.
Hi Jeff, That is a good idea but I set up the 737 Tech Group on FB and it is not used. Maybe I should publicise it better or use a different medium. I have not used Telegram before. facebook.com/groups/491086447951799
thank you for this great explanation. AEW&C aircrafts have the following caution: "The APU must not be operated during any takeoff." What might be the reason behind that caution?
I was not aware of that. Maybe it cant get the necessary inlet airflow at low speeds because of the Top Hat? Just a guess. Where did you get the info about the restriction?
The APU is certified to operate throughout the flight envelope with no restrictions; operators may do as they please, but they would not be due to certification or system operation limitations.
Hi Captain! Amazing video as always, thanks! I have a question: when on the ground, with a NG and powered by GRD source, so AC is available, and just before we are ready to go, we start the APU. So, since we have AC from GRD source, I assume that AC is being used to start the APU. But, during the APU start, I've notice the BATTERY DISCHARGE light to illuminate, and the DC AMPS showing a big negative value from the main battery. After seeing this, I was wondering If the source for AC power is a GRD source, the APU starts using DC power from the main battery. Despite the information I have that if AC is available, it will be used to start the APU. I was wondering if you can help me understand this. Thank you!!
The APU has a dedicated battery for starting. This is the normal source, the other being the Transformer-Rectifier Unit which gets its energy from the electrical bus (main engines, external ground cart).
Thanks for uploading this comprehensive information. If i can get answer for a question it will be highly appreciated. Can we boost APU in B737NG, like we can do it in A320's....as we have 131-9(A) installed....is there a possibility ?
Thanks for your reply Chris, appreciate that, actually someone asked me this question while comparing with A320, as it can be done as a DISCRETE OUTPUT function of ENGINE INTERFACE UNIT ( EIU ).....i agree with you, never heard of that for B737NG.....anyways thanks again.
It is possible that Boeing can change the rating/boost of the APU at build. For instance a -600 or -700 is likely to need a lot less bleed air for ECS than a -800 or -900. But this is just speculation.
@@ChrisBrady737 Yes it is a speculation, but i think it was not required. Else Boeing could have done it or must had kept it as an option to execute. Thanks again for your prompt response.
Hello captain thank for your crucial video I appreciate that . I have tow question : _ first one I saw some pilots when starting APU they move the switch from OFF to ON and spent it on ON for 10sec or greater then move it to START. so do you have any reason about that ? - what do you think to take an habitual of starting the APU on final ? Thank you again 🙏
Hi, thank you for your kind comments. The pause before moving to the START position was old advice for the Classics from Boeing years ago that is no longer valid. BTW the pause was only 1 or 2 secs as I recall. I would not advise to start the APU on final as you should always monitor the APU start for abnormalities and you cannot do that effectively on final.
Hi Joe, This link will take you to a page showing you the options for either the electronic version from Apple Books or a hardcopy printed version. www.b737.org.uk/ebook.htm Thanks for your support Chris
