Questions you had never asked before about B737

[Skymaniac]

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?:)

[gegemi]

What about the source off NNC ?

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

[Skymaniac]

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?

[FlyingStone]

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.

[tdracer]

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

[framer]

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?
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.

[parabellum]

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"

[framer]

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

[BBK]

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.

[FlyingStone]

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...

[latetonite]

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.

[parabellum]

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


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.

[glendalegoon]

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

[latetonite]

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.

[framer]

Hi para, my point was that you will have a list of messages in front of you is incorrect so you can't scan it immediately looking for "Bleed Duct Leak",.
The advice that it may come three or four down the list 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.

[Jwscud]

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.

[parabellum]

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.


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.

[latetonite]

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.

[FlyingStone]

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.

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?

[Centaurus]

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

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.

[ImbracableCrunk]

I use CWS from time to time, but I've always wondered what is the history of CWS with Boeings.

Anyone know about the origins of CWS?

[framer]

I do too, I enjoy setting up a bank angle on a base turn to land using it. I think I've read somewhere that on the -200's that it was all the automatics that they had originally ..... that could well be incorrect, it's just an impression I had.

[BOAC]

I think I recall alt hold, and CWS. How on earth did we manage with Doppler, Met and Airways charts and without the Magenta Line?:confused:

[Mach E Avelli]

The early 200 series had no vertical autopilot coupled modes, only CWS pitch. They did have alt hold, but some installations were so primitive that they required the pilot to engage it on reaching the required level-off. With no auto throttle either, so all climbs and descents required one pilot's hands on the wheel or ready to make corrections at all times. It was generally stable enough to allow one to finish that last cup of coffee.
BOAC, those days bred good handling and awareness, didn't they?

[Matey]

On Britannia Airways 737-200s only the Captain had HDG SEL. The F/O only had CWS in both lateral and vertical axes. Passing the Command Course meant both a pay rise and the luxury of HDG SEL! Alt Hld had to be manually engaged on reaching assigned level, having reduced the rate of climb/descent using CWS. No V/S mode either, but we did have VOR/LOC. All selected through massive rotary switches which engaged with a satisfying clunk. Ah...those were the days!

[parabellum]

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?


No, I really can't. We had the scenario given to us in the B744 SIM where an inboard engine broke away, up came all the messages, including fire warning at the top, it was played through to the end with us not jumping on the bleed leak, just to emphasis what would happen, I thought this might carry over to the B737 but obviously it doesn't! :O


I think this would be a good time for me to quietly slip out the door, unnoticed! :)

[glendalegoon]

centaurus, I'm sure you didn't mean decades of experience designing jet transports. the 737 came around in the 67 , so you are saying that boeing was busy designing jet transports about the time it was building B29s. While it was working on the B47, the 707 came much later.


Douglas had a much nicer autopilot. You want to hold pitch? Select Pitch Hold. Wow. Want to turn? Twist a knob. Want to hold speed? Select Speed or Mach hold. And the comparable douglas flew before the 737.

The CWS is a mystery of a waste. And I've seen new copilots land in CWS NOT KNOWING they were on autopilot. SHEESH!

[ImbracableCrunk]

And I've seen new copilots land in CWS NOT KNOWING they were on autopilot. SHEESH!

Wow. I've landed with a Y/D on on a calm day in a turboprop, but that's a different level of wow.

[AvEnthusiast]

Well if you loose one generator, the other side is going to supply the failed side by means of cross-ties, and then there is the APU. Assuming APU not connected or available when you do the checklist, I reckon Boeing has a nice philosophy for checklist I mean every step and checklist directs you to other portion of checklist if required to be carried out.

[JammedStab]

On Britannia Airways 737-200s only the Captain had HDG SEL. The F/O only had CWS in both lateral and vertical axes.

Alt Hld had to be manually engaged on reaching assigned level, having reduced the rate of climb/descent using CWS. No V/S mode either, but we did have VOR/LOC. All selected through massive rotary switches which engaged with a satisfying clunk. Ah...those were the days!

Correct. CWS was used quite a bit on the -200 as stated above.

Plus in the sim, we knew that on the circling approach,we had a good chance of getting a missed approach with an engine failure so the autopilot was left on during final as low as possible. If no missed given, disengage in the flare, if a missed approach given, you now had an easy and smoothly done way to level off for acceleration by quickly selecting Alt Hold when at acceleration height. Perhaps more of a sim thing.

[PPRuNeUser0190]

I guess what the thread starter means is that the transfer bus remains failed after the NNC (half of the overhead panel lights ON :)) .

What I would do is check the checklists at least and apply some common sense on which checklists to do. That way you have an idea which systems you have left. IMO it is one of the most tricky failures on the 737.

PS: A nasty result of a transfer bus 2 failure is that the flap indicator does not work anymore. Some crews mistakenly see this as flaps not working anymore... Amber bar on PFD still shows correctly and will move when flaps come out.

[Australopithecus]

The 737 does require a bit of old-fashioned systems knowledge since it lacks a spoon-feeder (EICAS). I like flying things with EICAS or ECAM, but am comfortable enough in the physical world to know when a major failure will manifest itself in related sub-systems warnings. As should anybody who has a driver's licence, to say nothing of a pilot's certificate.

Sometimes deep science on the flight deck is useful, but often an imperfect systems understanding can lead you astray. The designers thought of most things that need redundancy or check valves or relays. But it is always useful to workshop scenarios both to review systems knowledge and to exercise your planning and adaptation muscles.

Control Wheel Steering....the -200 F/Os only mode. It may surprise some Boeing pilots to learn that the Airbus FBW performs exactly like CWS...take your hands off and it just keeps doing the last thing you commanded.

[Pontius]

CWS is an excellent tool when using the Unreliable Airspeed checklist. Set the attitude and power and just monitor the performance instruments. Much easier than having to actually hand-fly the attitude. I know, I know, Skygods; before the inevitable bitchy remarks about how we should all be able to hand fly to within a gnat's :mad: I'm saying it's just easier to let the plane take the strain, not that I can't hand fly and that CWS is a great way to do it.

[prodi9y]

I have 2 items in the 737 Classic cockpit that none that I spoke to is able to answer. They are trivial but will be nice to know.

What it is call "Dome White" and not Dome light? Specifically, the light is not even white..

The other is about the flaps 2. Is it carried over from the 737-100s? We have used flaps 10 occasionally when the aircraft ahead is closing in on approach and we do not want to use Flaps 15 without gear down but why is there a Flaps 2?

[RAT 5]

Flaps 2, in a fixed speed schedule, is 180kts. This could often be an ATC requirement on approach. In the very early days I've no idea if there was any advantage gained for a F2 takeoff. I never saw any figures for this, but that was in 80"s.

[BOAC]

It may surprise some Boeing pilots to learn that the Airbus FBW performs exactly like CWS...take your hands off and it just keeps doing the last thing you commanded. - it certainly does 'surprise' us since the word exactly is wrong!

[FlyingStone]

Flaps 2, in a fixed speed schedule, is 180kts. This could often be an ATC requirement on approach.

Now if only some people would be convinced that aircraft won't fall off the sky if you select flaps 2/10/25, we'd be off to a very good start...

CWS can also be used in CWS P mode when in climb - to compensate for VNAV (MCP) SPD incompetence :)

[Denti]

To be honest i don't use 2 all that often, but it is sometimes useful. 10 and 25 on the other hand are normal take off flap settings and therefore used quite often. Much less often during approach though, although it can be sometimes advantageous to do so.

[BARKINGMAD]

The 73NG, when locked onto the standard 3* G/S, will run away with the speed, unless

1. The headwind component is in the teens

or

2. Flap 10 is selected, much to the horror of those who exclaim "that's non-standard!" (My reply is "why did Mr Boeing bolt in that there slot?!")

Just another piece of info for the uninitiated when they start to fly this slippery beast! :)n

[Jwscud]

Flap 2 - aka "the gentleman's flap"

I find it very useful. Either if given speed 180 at high weights with the '1' speed around 190ish, or as another method of losing excess height. Rather than speedbrake clean/250 knots, using F2 220/230 knots is a very effective way of getting back on profile (~1500fpm) and smoother than using the speedbrake.

I use Flap 10 almost daily on the NG, and Flap 2 at least a few times a week. Flap 30 is fairly often required as an intermediate setting if you've got a bit of a tailwind trying to make the gate for F40 too.

Now if anyone can tell me how to consistently grease Flap 40 landings...

[JammedStab]

To be honest i don't use 2 all that often, but it is sometimes useful. 10 and 25 on the other hand are normal take off flap settings and therefore used quite often. Much less often during approach though, although it can be sometimes advantageous to do so.

Flaps 2 was used a lot on the -200 in my experience for takeoff. Compared to flaps 1, it gives several thousand extra pounds of capability at some airports depending on the situation. Also, it gives about 5 knots lower v-speeds which always felt kind of fast to me.

For the newer types, I guess, it is just a holdover from the old days.

[medflyer]

I disagree that CWS is a waste. It is merely a tool that can be useful in some specific situations.

For example, I like CWS P when the NG is doing the hobbyhorse routine in a VNAV climb. It will still level off (capture an altitude) in this mode. If you enter the mode without selecting N1 on the A/T then the power will come back to hold the selected speed. If you leave it in speed it will function like V/S, which has its place too. Although some shy away from full CWS as it will sail right through an altitude selected on the MCP, there is actually a way to ensure this will not happen: breaking out the autopilot through pressure on the controls in pitch and roll will get you into CWS but with 'CMD' on the FMA vs 'FD', which is what you will see if you get to CWS by simply pressing the button.
FD= no alt capture.

[ImbracableCrunk]

Although some shy away from full CWS as it will sail right through an altitude selected on the MCP, there is actually a way to ensure this will not happen: breaking out the autopilot through pressure on the controls in pitch and roll will get you into CWS but with 'CMD' on the FMA vs 'FD', which is what you will see if you get to CWS by simply pressing the button.

Or you could just de-select the current V mode. Much less muscle-y.

[medflyer]

Agreed, however that only gets you CWS P, not the full CWS experience :ok:

[ImbracableCrunk]

The only time I'd use full CWS would be severe turbulence.

[Tom!]

I also have a question that has been bothering me for a while:

In the case of a loss of all generators (dispatched with APU INOP) and not recoverable.

Apart from a dozen other things you obviously also lose the elec stabtrim. Having a look at the checklist it says to land with flap 15. But since only half of you anti-skid system is working (inboard only?) it seems to be a better idea to land with normal landing flap 40? (flap indicator not working as well)

Establish and manually trim it out on long final with F40 and be careful in case of a go-around with the trim requirement, or follow the stabtrim INOP NNC and go with F15 and taking the extra speed into account for the LDR with partial anti-skid.

The loss of both generators checklist doesn't seem to have a preference.

[No Fly Zone]

From the original: "To start with, I have an electrical question regarding its electrical system:"

I'm certainly glad that your question about the 'electrical system' was an 'electrical question and not perhaps a hydraulic question. Whew :rolleyes:. That was a close call!

More seriously, I hope you received a response that you understand. :ok:
(Tip that may help: read it out loud, even to yourself, :p -and before pushing the Send, Publish or Post buttons:confused:. Been there :( and done that:ugh:. Better luck next time.

[ZFT]

Was it a bottle of red or white wine?

[stilton]

' On Britannia Airways 737-200s only the Captain had HDG SEL. The F/O only had CWS in both lateral and vertical axes. Passing the Command Course meant both a pay rise and the luxury of HDG SEL! Alt Hld had to be manually engaged on reaching assigned level, having reduced the rate of climb/descent using CWS. No V/S mode either, but we did have VOR/LOC. All selected through massive rotary switches which engaged with a satisfying clunk. Ah...those were the days!
Matey is offline Report Post Reply'



Sounds exactly like a B727 :ok:

[OhNoCB]

Why no check valve from the APU bleed to stop back pressure?

[FlyingStone]

My FCOM shows that there is one...

[OhNoCB]

Hmm mine shows that there isn't! Have just double checked to make sure. Wouldn't be the first time that I have pondered questions arising form this FCOM which have been answered by better manuals.

[IFixPlanes]

I Hope you accept the AMM (Aircraft Maintenance Manual) as an "better manual".
All B737 (100-900) have a check valve in the APU bleed line.
In addition: I know it out of (more than) 25 years as a mechanic, working on this aircraft.

[ManaAdaSystem]

I want to know what I am supposed to do with the yaw damper indicator?

[IFixPlanes]

One thing is to check the system on ground during taxiing. You have a short movement in opposite direction the airplane drives in a curve.

[BOAC]

Back in 'the old days' (73-2) it used to be part of the instrument checks during taxy ("What are they....?")

[Denti]

I want to know what I am supposed to do with the yaw damper indicator?

It's not there anymore in newer planes, so i guess it can be seen as superfluous information.

[ManaAdaSystem]

Yaw damper switch on, YD works. Switch off, it doesn't.
Probably why they removed the instrument. I have never used it for anything.

When you did the instrument scan, did you check the instrument or the system?
What did you look for? It moved! Thank God! :)

Have any of you found the two leading edge flaps on each wing?
I must be blind because I can only find one. I've been puzzled about this for years, but I'm scared it's just me who can't find the other one. :O

[BOAC]

If you are asking as a pilot and you HAVE an indicator, what does your company manual tell you to do? If nothing, then happily ignore, stop worrying and return to blissful ignorance?

[TURIN]

Yaw Damper Indicator was used every night during the Daily Check. Or was it Weekly? It's been a while.

[ManaAdaSystem]

Some of our aircraft have it, some don't. I'm not worried, just curious. Our manuals doesn't tell us to do anything with it.

So, when you checked it, did you check the instrument, or could you check if the YD system was operating normally? Checking without knowing what you are checking seems rather pointless to me.

Respectfully.

[framer]

What mechanism/ component moves the control yoke forward a fraction when flap is selected on the ground?
Look closely, when you go from clean to flap1/5/10 after engine start, the control yokes move forward a fraction.
( my guess is the elevator feel computer)

[BOAC]

So, when you checked it, - movement in opposition to yaw checked both damper and instrument.

[Clandestino]

Are -700 and -800 flaps and slats interchangeable i.e. same P/N?

[de facto]

Back in 'the old days' (73-2) it used to be part of the instrument checks during taxy ("What are they....?")

Was also part of Astraeus procedure a few years back.

[B737900er]

I was told the B737 had a limitation on the maximum wind speed it could taxi in.

I was told it was 65kts. I could not find this in any of my company manuals nor the AFM.
The only place on the internet i have seen it written is on B737.org.

Is there any truth?

[RAT 5]

Have you got carbon or steel brakes or only a brake parachute?

[B737900er]

Rat5

if that was directed at my question then we use both Carbon and Steel brakes and some times hopes and dreams of stopping :E

[BOAC]

As far as I recall, there are two figures for 737:

1) 40kts for Airstair operation
2) NOT a limit, but if taxied or 'open' parked in wind speeds (no, Rat, not Ryanair taxy speeds:D) exceeding 65kts, an engineering check is (?was?) required.

[B737900er]

BOAC,
Thanks for the answer but where can i reference this? Its not mentioned in my company manuals nor AFM?

[Tom!]

It's mentioned in my FCOM2, Chapter 1 "Doors and windows"
CAUTION: Do not operate the entry or cargo doors with winds at the door
of more than 40 knots. Do not keep doors open when wind
gusts are more than 65 knots. Strong winds can cause damage
to the structure of the airplane.

[RAT 5]

I once flew for an airline when hats were still in fashion. They had a temp'c limit when shirt sleeve oder was allowed. I asked about wind speed for the hated caps and was met with a dumfounded look.

[B737900er]

TOM- Im not talking about the doors I'm talking about taxying!

Ive heard of Head, wind, tailing limits but never taxi.

[BOAC]

I don't know where you will find it if it still exists. Ask your company? It is NOT a 'taxy' limit' - it is a wind speed above which a 737 ANYWHERE in the open needs (?used to need?) an engineering check. You could be sitting on stand;a/c parked overnight on the apron;taxying; whatever. Obviously headwinds as in 'flying' do not count. I assume it is to do with rudder maybe? Anyway, it isn't very likely to bother you.

[despegue]

BOAC!

We do not have this limit so this was probably a Company Procedure.

[BOAC]

Could also be one that has been withdrawn? I'm sure the airstairs limit is still there. Ask Boeing?

[Jwscud]

http://www.aaiu.ie/node/667

That report regarding damage to a 738 rudder during a thunderstorm the previous evening makes interesting reading. Well handled by the crew but more significant damage could have really woken them up.