19AB67

[FSX] DC BAT BUS MAIN: No error message?! Land asap?

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Hi folks, 

on my current flight CLX778 ELLX to MMMX I got close to 5350N the following error messages: 

FLAPS PRIMARY
   >NO AUTOLAND
   >YAW DAMPER UPR

The status page on the lower CRT, I get even 3 pages full of messages: 

E/E CLNG CARD
ENG x OVHT LP B
ENG x FIRE LP B (x = 1..4)
MAIN DK FIRE LOOP y Z (y=1..8, Z= A; B)
CLAP CONTROL
STALL WARN SYS R, L
STAB AUTO TRIM

I had a suspicion, and yes, a sneak view into the FAILED ITEMS page shows alone. 

DC BAT BUS MAIN

Well, none of the defects refers to the DC battery main bus, 

and nothing directly implies to land asap. 

1. Why is there no DC BAT BUS MAIN message or is it just obvious?

2. Usually no ambiguity is left in aviation...

3. Should I land asap? (MMMX with some flap issues calls for a diversion, does it not?)

4. Why is there no main bus backup, or is the STBY BUS totally fine, and I don't have an issue at all? 

Thanks in advance, 

Andre(as)

 

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6 minutes ago, 19AB67 said:

1. Why is there no DC BAT BUS MAIN message or is it just obvious?

I'll defer to someone with more knowledge about the plane, specifically.

6 minutes ago, 19AB67 said:

2. Usually no ambiguity is left in aviation...

This assumes everyone knows everything, always. Additionally, this assumes the messaging needs to specifically match the issue.

When the 777 at LHR crashed short because of ice crystals in the engine, did the EICAS display "ICE IN ENGINE," or a slew of related messages "ENG FAIL" (and so on)?

8 minutes ago, 19AB67 said:

3. Should I land asap? (MMMX with some flap issues calls for a diversion, does it not?)

Use the QRH.

8 minutes ago, 19AB67 said:

4. Why is there no main bus backup, or is the STBY BUS totally fine, and I don't have an issue at all? 

You have 4 generators - one in each engine.

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2 minutes ago, scandinavian13 said:

This assumes everyone knows everything, always.

I wasn't precise enough: In QRH there messages like STBY BUS MAIN = The main standby bus is not powered. 

One could expect that the system also provides such information for the DC BAT BUS MAIN. 

5 minutes ago, scandinavian13 said:
15 minutes ago, 19AB67 said:

3. Should I land asap? (MMMX with some flap issues calls for a diversion, does it not?)

Use the QRH.

Ok, no advice to land from any of the messages. 

6 minutes ago, scandinavian13 said:
16 minutes ago, 19AB67 said:

4. Why is there no main bus backup, or is the STBY BUS totally fine, and I don't have an issue at all? 

You have 4 generators - one in each engine.

Yup, cool I continue. 

Uhm, still unsure due the seemingly lost overheat and fire loops. 

 

And thanks for your swift answers. 

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3 minutes ago, 19AB67 said:

Uhm, still unsure due the seemingly lost overheat and fire loops. 

This is where that whole "pilot" thing comes into play.

Your plane. Your decision. There's a reason people are still up front.

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As Kyle says, this is one of those situations where you earn those big bucks you're getting paid as a B747 Captain!

The important thing to remember when you get a failure like this is that the QRH only considers individual failures. Once you start getting multiple failures (like this) you start going outside the scope of the QRH and start having to make some decisions. The failure of one fire loop in isolation, for example, is not necessarily going to require an immediate landing. But in this situation it's not just one that's failed: it's all of them.

Think about this: do you really want to be over the Atlantic and/or flying for an extended period with no fire detection or extinguishing capability?

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11 hours ago, 19AB67 said:

1. Why is there no DC BAT BUS MAIN message or is it just obvious?

2. Usually no ambiguity is left in aviation...

3. Should I land asap? (MMMX with some flap issues calls for a diversion, does it not?)

4. Why is there no main bus backup, or is the STBY BUS totally fine, and I don't have an issue at all?

Unfortunately, I don't have any DC electrical description for the Cargolux aircraft so I cannot verify the accuracy of the messages you saw, but I will try to answer your questions as best I can. .

1. The B744's AC and DC electrical systems are not as simple as you might think, because Boeing have designed a lot of redundancy into all of the systems of the B744, including the electrics.  Just to give you a flavour, the electrical Busses on a Passenger variant consist of an APU Battery Bus, an APU Hot Battery Bus, an APU Standby Bus, a Captain's APU Standby Bus, a Co-pilot's Standby Bus, a Main Battery Bus, a Main Hot Battery Bus, a Main Standby Bus, a Captain's Transfer Bus, a First Officer's Transfer Bus, DC Busses 1 to 4 and, last but not least, the four AC Busses. 

You might see a >BAT DISCH MAIN careted message but I doubt if you will ever see a DC BAT MAIN message because, to the best of my knowledge, it doesn't exist.  This is down to the clever system design, because the four Main DC Busses are each powered directly from their own TR Unit and receive their power from their resepctive Main AC Busses.  The Main Battery Bus is normally supplied from the No.3 DC Bus, but with four TR units providing DC power.to each of the four DC Busses and with them all linked together by a DC Tie Bus, even in the worst case scenario if the No. 3 DC Bus was to eventually fail the Main Battery Bus will still be supplied by the Main Hot Battery Bus and this gets its power from - you gessed it - the Main Battery or Battery Charger.  Simple, isn't it?!

2. I have a feeling the FCOM and QRH  Procedures are not type specific and so you can't expect them to cover all of the different verified aircraft liveries exactly.

3. Not necessarily.  The only time you really need to land ASAP is if the aircraft is on fire or if you are getting very low on fuel.  Each situation will be different and the QRH can't possibly cover every eventuality, but It is usually much safer for one pilot to concentrate on flying the aircaft using an autopilot whilst the other pilot sorts out the problem.

4. You don't have an issue - see 1 above!      

Edited by berts
typo
  • Upvote 2

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On 9/15/2018 at 12:10 AM, 19AB67 said:

FLAPS PRIMARY
   >NO AUTOLAND
   >YAW DAMPER UPR

The status page on the lower CRT, I get even 3 pages full of messages: 

E/E CLNG CARD
ENG x OVHT LP B
ENG x FIRE LP B (x = 1..4)
MAIN DK FIRE LOOP y Z (y=1..8, Z= A; B)
CLAP CONTROL
STALL WARN SYS R, L
STAB AUTO TRIM

Complicated.

e.g. STALL WARN SYS R, L

This must be due to a sensor power failure rather than due to power to the stick shaker motors or MAWEA.The stick shaker motors are powered by the Main Battery Bus, but the aircraft would not know that the stick shaker motors were unpowered. There is no feedback from the motors.

FLAPS PRIMARY

I see some components of the flap system are powered by the main battery bus, but (in some cases) messages wouldn't be generated until you actually tried to move the flaps. There was a debate on another forum regarding what would happen if you lost DC power to the Flight Control Power Supply Units (FCE's). If you removed DC power (only), are you affecting the user systems or just the FCEs?

I assume your problem is some kind of short on the battery busses. If there was a lot of current being drawn, the Remote Control Circuit Breaker/s (RCCBs) feeding the battery busses might have tripped (opened) before the short had time to drag down DC Bus 3 and the other DC busses. You would normally expect a power-related message if a TRU couldn't produce enough volts because of a short, but if the RCCBs acted before the current and voltage abnormalites were detected by the Generator Control Units, you wouldn't get a #3 TRU message and the #3 DCIR wouldn't trip.

AFAIK, there are no voltage sensors on the Bat Busses themselves. If you looked at the battery indications, however, you might see that they were using very little current if the Remote Control Circuit Breaker/s for the Bat Busses busses had tripped and the battery relays were in their normal positions. In the case where the RCCBs had tripped, the batteries(or battery chargers in TRU mode) would not be commanded to take over from #3 Main DC Bus.

This stuff is a lot easier to understand if you have a detailed schematic )))

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7 hours ago, Qavion2 said:

FLAPS PRIMARY

I see some components of the flap system are powered by the main battery bus, but (in some cases) messages wouldn't be generated until you actually tried to move the flaps. There was a debate on another forum regarding what would happen if you lost DC power to the Flight Control Power Supply Units (FCE's). If you removed DC power (only), are you affecting the user systems or just the FCEs?

I assume your problem is some kind of short on the battery busses. If there was a lot of current being drawn, the Remote Control Circuit Breaker/s (RCCBs) feeding the battery busses might have tripped (opened) before the short had time to drag down DC Bus 3 and the other DC busses. You would normally expect a power-related message if a TRU couldn't produce enough volts because of a short, but if the RCCBs acted before the current and voltage abnormalites were detected by the Generator Control Units, you wouldn't get a #3 TRU message and the #3 DCIR wouldn't trip.

AFAIK, there are no voltage sensors on the Bat Busses themselves. If you looked at the battery indications, however, you might see that they were using very little current if the Remote Control Circuit Breaker/s for the Bat Busses busses had tripped and the battery relays were in their normal positions. In the case where the RCCBs had tripped, the batteries(or battery chargers in TRU mode) would not be commanded to take over from #3 Main DC Bus.

This stuff is a lot easier to understand if you have a detailed schematic )))

Thanks for the detailed technical information which is very interesting. The FLAPS CONTROL message is one of the more obvious clues here, because it is generated by the loss of the Primary Trailing Edge Flaps DC control.  This sort of scenario is where good airmanship as well as your detailed technical knowledge and experience is always handy to have!  For this reason alone, having a Flight Engineer on board at times like this was usually worth his weight in gold!  🙂    

Seeing so many EICAS and Status messages appearing all at once can be quite daunting to any pilot at first, but provided they give themselves sufficient time to work through each abnormal item starting at the top and going through each one methodically using the correct QRH procedures then they should always be able to handle the situation safely.  It is interesting to note that the FLAPS PRIMARY QRH procedure is quite short, whereas the FLAPS CONTROL message gives the pilots a lot more information on what to do (and not to do!) in this particular QRH procedure.  Clearly, the Alternate Flaps will be necessary for extension as well as retraction (the worst case scenario here is likely to be if it occurs immediately after a heavyweight takeoff). 

Another thing to look for on the real aircraft that is usually not mentioned in the abnormal checklist procedures, but always worth checking, is to see if a circuit breaker has popped.  Unless there is some obvious and very good reason not to do this, a single reset of the CB is permissible because it just might clear the fault(s). 

Edited by berts
typo

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12 hours ago, berts said:

Another thing to look for on the real aircraft that is usually not mentioned in the abnormal checklist procedures, but always worth checking, is to see if a circuit breaker has popped.  Unless there is some obvious and very good reason not to do this, a single reset of the CB is permissible because it just might clear the fault(s). 

Indeed. The Main and APU Battery Bus RCCBs have corresponding CBs on circuit breaker panel P6 in the cockpit. However, I don't know what the general policy is for resetting a circuit breaker of this magnitude. It guess it would be similar to resetting a GCB, but.. I don't know for sure.

You can force the battery busses to use battery (or battery charger?) power using the Standby Power switch, but if there is indeed a short on one or more battery busses, you may do more harm than good. There are also RCCBs on the battery side of the battery busses, but if they didn't trip or didn't trip fast enough, you might affect the Hot Battery Busses, too. 

Some of those fire loop messages are a little worrying. I thought the APU Bat Bus provided power for the B loops. I can't easily think of a scenario where both the APU and Main Bat busses would be affected. Only the PMDG team would know what this scenario involves.

 

12 hours ago, berts said:

The FLAPS CONTROL message is one of the more obvious clues here, because it is generated by the loss of the Primary Trailing Edge Flaps DC control. 

Not sure. This comes back to whether or not the flap system can detect a DC power loss prior to flaps being used. Flap position data loss will be detected prior to flap use. Flap position transmitters use voltages from the FCEs. However, these voltages are derived from the overhead panel AC CBs. The FCE's do send (FCE status) data to user systems, but the text in the manuals is a little ambiguous regarding how (and when) that data is used.

Unfortunately, without an airplane to experiment on, we probably will never know. I did pull FCE CBs a few years ago (for the purposes of sim development), but the CB combinations I used didn't give a full picture of their effect. Some combinations gave some pretty weird effects (such as the pitch limit indicators appearing on the PFDs with the flaps up).

Cheers

 

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On 9/17/2018 at 5:22 AM, Qavion2 said:

Some of those fire loop messages are a little worrying. I thought the APU Bat Bus provided power for the B loops. I can't easily think of a scenario where both the APU and Main Bat busses would be affected. Only the PMDG team would know what this scenario involves.

Yes, some of those messages are worrying - period!  On the 744 Pax version I am familiar with the APU Battery Bus provides power to the Engine 1-4 fire/turbine overheat detections loops A and B from the APU battery

On 9/17/2018 at 5:22 AM, Qavion2 said:

Unfortunately, without an airplane to experiment on, we probably will never know. I did pull FCE CBs a few years ago (for the purposes of sim development), but the CB combinations I used didn't give a full picture of their effect. Some combinations gave some pretty weird effects (such as the pitch limit indicators appearing on the PFDs with the flaps up). 

Agreed. Not even a full-size zero flight time simulator can be a perfect replica of the real aircraft's handling characteristics and performance.

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