Questions you had never asked before about B737
 

Hi everybody,

I'd like to open this discussion to share our thoughts and knolewdge about those questions we never dare to ask about Boeing 737, the most built aircraft ever (as far as I know).

To start with, I have an electrical question regarding its electrical system:

Scenario: you've just had a single generator failure and had the cockpit scattered with lights in the overhead panel: BUS OFF, its associated fuel pump Low Pressure light, some Window Heat lights, etc.

Question: Which checklists are you using and in which sequence?

I would read and do the BUS OFF NNC, provided its associated transfer bus has switched to the opposite generator bus; in this case the first checklist would be TRANSFER BUS OFF NNC. And in case we have ended up with no success in connecting the APU to this generator bus...

What then? Would you continue reading any checklist for any of the inoperative system till you've got all of them covered? And in what order? Is it relevant?

What do you think?:)

What about the source off NNC ?

Pretty straight forward CL :
APU -> continue.
No APU -> continue you will not.

Yep,

As you stated it is very straight forward in the classic. I don't know in the NG and don't remember too much about it coz i flew it few hours 4 or 5 years ago.

What I meant in the question is:

After you have done the NNC and the APU cannot be connected to the bus... Do you keep on doing checklists while you divert to an appropriate airfield or just keep the lights illuminated?

1. Cessna 172 is the most sold aircraft to this moment.

2. B737 requires at least basic system knowledge even for the simplest failures (e.g. generator failure) due to lack of ECAM/EICAS. If you get 10 lights at the same time, it's most likely due to a single (electrical) failure and you don't need to do 10 NNCs.

In any case, using your system knowledge, you can do the following workflow (repeat as neccessary):

Warning Light -> Identify and decide on main reason -> NNC -> Recall -> (if any lights illuminate or remain illuminated) -> Identify ... -> NNC -> Recall -> ....

As for continuing to do checklists... Fuel & Hyd pumps, etc. simply won't work if they don't get electrical power. You may be able to start APU at lower (than cruise) level and then proceed to destination with APU running. In this case, you just put APU GEN on bus and you don't need to reconfigure half of the cockpit again to get things normal.

To be a bit anal...:}
The 737 is so far the most built commercial jetliner - the 8,000th 737 was delivered a week or so ago. There were other large aircraft that more were built, for example there were over 12,000 B-17s built. It could be argued that the 737 is the most built airliner, depending on how one counts the DC-3. There were something like 16,000 aircraft of the basic DC-3 design, most were built as C-47s, although many were converted to airliners after WWII.

:E

The QRH assumes that all lights are " reviewed".
In my mind that doesn't necessarily mean the checklist is actioned, but it would be a good idea to review them all in case something else is going on. Part of that reviewing process might be checking the checklist for further considerations etc.

May not apply to the old 737 but a point worth remembering is that after, say, an engine detaching you will have a list of messages in front of you, scan it immediately looking for "Bleed Duct Leak", it may come three or four down the list, (possibly get a fire warning first, even though the engine has left you!), but you are dumping your pressurisation over the side so you need to fix this one first. If you don't it will lead you into a rubber jungle, emergency descent etc. none of which you need whilst dealing with "Engine, severe damage and separation"

That doesn't even apply to the newest 737's.

On the 737 300/400 wasn't there a condition if you lost the TR3 then you would see a lot of captions illuminated. Long time ago so maybe my memory playing tricks.

You'd get no indication of TR3 failure (except no voltage on TR3) until G/S capture on AP or FD ILS Approach - then you would get the mentioned lights...

The trouble shooting in the 737 is in my opinion based on the loss of a power source. We are talking generators, so AC power.

Once you would have a DC problem, for instance a DC bus 1 failure, you are looking into another can of worms.

Indeed, prioritizing the tasks at hand is up to the crew.

I would be looking at a 'Land Asap' and live with what is lost.

I don't have the manuals to hand but you can rest assured that if wing ant-icing is achieved using bleed air, (as is the case on the bigger Boeings), then, should an engine fall off, you will, almost certainly, have a serious bleed duct leak.

what I would like to know is who the heck came up with control wheel steering (CWS)? what a freaking waste!

Parabellum: If you would having an engine separating your airplaine, and like you said, at altitude, I still do not think a bleed leak would be your primary concern.

Hi para, my point was that is incorrect so you can't .
The advice that does not apply either.
I thought it worth pointing out that the advice was wrong in order to prevent confusion for people (like yourself) who are not familiar with the 737.

CWS is quite useful, especially if you get stuck in ALT ACQ with a hoofing RoC or RoD, or in nasty turbulence.

The other nasty little gotcha that people don't think about is that if you lose one RA, you lose the autopilot and FD approach mode at GS Capture dumping you back to raw data, which you might not have expected.

.


Next time in the SIM get the instructor to set it all up, give an engine separation and you then ignore the bleed leak until you have done those items you consider more important. (Which are?).


I'm not making this up, it is what I was taught along with many others, if you don't agree go talk to Boeing! :)


Framer: Yes, I didn't realise the modern 737 didn't have EICAS, but watch out for a bleed duct leak, nevertheless.

Parabellum: I am almost daily in the B737NG simulator, as an Instructor.
I am well informed about the procedures of the B737, the programmed problems, the BOEING advise how to cope with them, starting with the QRH and the latest FCTM.

But thanks for the advise.

Even if you had an engine separation, you'd only have a single bleed duct leak. In B737, left and right bleed ducts are isolated during normal operations, since isolation valve is in closed position when you have both engine bleed switches ON (regardless of actual valve position / pressure) and both pack switches AUTO/HIGH.

For example, with left engine separation, right engine bleed, duct and pack would remain intact and therefore provide sufficient pressurization - even at normal cruising levels.

Would you care to provide a probable scenario where an engine separation would cause a dual bleed duct leak (and resulting pressurization failure) on B737?

In fact CWS mode is a useful fall-back if manual flying in severe turbulence since the extra control forces involved with CWS mode minimise the tendency for the pilot to over-control in pitch and roll which in turn could, in the worst case, result in an unusual attitude in IMC. To answer your erudite question, however, it was the manufacturer based upon decades of experience of designing jet transport aircraft.