744 Forum

Hi,

I was trying to simulate a single FMC failure. For example, the master FMC is on left and I failed the left FMC. Won't I get a line across the LNAV and VNAV due to loss of FMC computed data?

Regards,

Hi,

the selection of the master FMC is automatic when just one FMC is available. In your situation, the right FMC is the master, even though the selector is set to Left.


Regards,

|-|ardy

Hi Hardy,

Am I misreading your answer or are you saying that in the event of the left FMC failing it automatically selects the right FMC?

It was my understanding that you had to physically move two switches to get the right FMC over to the left side -- both the FMC selector and nav source selector must be moved to the right FMC. Thanks.

Jon D

Hi Jon,

for LNAV/VNAV roll and pitch modes the available FMC is selected automatically (that was the original question).

For the A/T (for example) the available FMC must be selected manually with the FMC master switch.

For the captain's PFD/ND/CDU the available FMC source must be selected manually with the captains NAV source selector.

For the F/O's PFD/ND/CDU the available FMC source must be selected manually with the F/O's NAV source selector.


|-|ardy

Okay. I think I see what you are saying: When the checklist has you reselect LNAV/VNAV, it's because you selected the right FMC to get the autothrottle back and in doing so it knocked it out of LNAV/VNAV? The LNAV/VNAV function automatically switched over to the right FMC when the left FMC failed?

QuoteA single FMC is failed: ~ FMC selector ..................................... Select operable FMC ~ Reengage the autothrottle. ~ NAV SOURCE selector ...................... Select operable FMC ~ Reselect LNAV / VNAV as required.
--PROCEDURE COMPLETE -

In an earlier PSX version, when the master FMC failed, LNAV/VNAV disengaged.

Later on, Peter told me that this wouldn't happen on BA aircraft; the FMC selection should be automatic for the AFDS, so you need not fiddle with the master switch during critical flight phases. I modified that accordingly in one of the last updates.

As far as I know, switching the master FMC will disengage the A/T only, nothing else.

Thanks. Peter would know.

I would think that you have programmed it to do automatic switching. However, the 44 that are on my company fleet sadly do not have this option. I would have to manually reselect the master FMC for a respective failed FMC. Is it possible that you have a option to do both?

QuoteAs far as I know, switching the master FMC will disengage the A/T only, nothing else.

That is a true statement. But in the above scenario with a single, controlling FMC failure (captain's side), it looks like the A/T will disengage even before you switch the master FMC selector to the FO's side. This if for the CF6 engines so maybe there's a difference.

The autothrottle disconnects if:
 Autothrottle disconnect switch selected.
 Autothrottle arm switch off.
 Autothrottle faults.
 Two engines inoperative.
 Any EEC changes to the alternate mode.
 Reverse idle selected.
 FMC Master selector changed.
 The controlling FMC fails.
 Two FMCs inoperative.

QuoteSingle FMC failure
 FMC inoperative requirements are shown in the FCOM limitations section and in the DDG.
 Symptoms of an FMC failure:
 EICAS: FMC LEFT/RIGHT.
 If the left FMC fails and the FMC master selector is on L:
 Autothrottle failure. EICAS: AUTOTHROTTLE.
 Autopilot operates in a degraded mode. Degraded autopilot mode (EICAS >AUTOPILOT) means roll is level and pitch is the pitch snapshot at the time of failure. Pilot with an operating ND becomes the PF. Select HDG hold and ALT hold on the MCP.
 The ND displays MAP and VTK (VNAV track). LNAV, and VNAV are not available. Heading select and FLCH
may be used if necessary.
 TIMEOUT-RESELECT and/or ND blank.
 Use the QRH and use the source selectors to choose the operating FMC. All operations may be restored after an operational FMC is in use.

When this degraded mode occurs, I wonder what FMA you get.

https://drive.google.com/file/d/0B-WRh0Hf7VdZaHVYWl9pcnNGN2s/view?usp=sharing

Quote from: emerydc8 on Tue, 16 Feb 2016 02:21
That is a true statement. But in the above scenario with a single, controlling FMC failure (captain's side), it looks like the A/T will disengage even before you switch the master FMC selector to the FO's side.

What is the problem here? PSX works exactly like that (I don't comment about the LNAV/VNAV issue).

Cheers,

There is no problem. I just wanted to point out that in the scenario where you lose the master FMC, the A/T disengages as soon as you lose it -- not when you switch the master FMC selector to the other side.

I am interested in knowing if the FMA continues to show LNAV and VNAV in this "degraded" AFDS mode mentioned in my post above or whether you see something else.

Quote from: emerydc8 on Tue, 16 Feb 2016 02:21

QuoteAs far as I know, switching the master FMC will disengage the A/T only, nothing else.

That is a true statement. But in the above scenario with a single, controlling FMC failure (captain's side), it looks like the A/T will disengage even before you switch the master FMC selector to the FO's side.

Yes, it does this also before, -- also in PSX.

My statement was just a reply to this:

QuoteWhen the checklist has you reselect LNAV/VNAV, it's because you selected the right FMC to get the autothrottle back and in doing so it knocked it out of LNAV/VNAV?

The selection did not disengage LNAV/VNAV, it just disconnected the A/T.

In PSX, the A/T disconnects not only when moving the master FMC switch, but also in the event of a failure of that FMC which is driving the A/T.

Quote from: hellowk on Tue, 16 Feb 2016 01:39
I would think that you have programmed it to do automatic switching. However, the 44 that are on my company fleet sadly do not have this option. I would have to manually reselect the master FMC for a respective failed FMC. Is it possible that you have a option to do both?

I'd like to check whether it's really a company option.

Any further comments from pilots and engineers?

Also, you said you expected a (yellow) line through the LNAV/VNAV mode words. In PSX, there would be a mode change to HDG HOLD and V/S instead of a mode fault.

Hi Hardy,

If you look at the second page of the link I posted above under dual FMC failure, it says that in the degraded autopilot mode, "the FMA roll mode is HDG HOLD" (although I'm not sure if they mean it automatically goes to HDG HOLD or you should select HDG HOLD). As for the pitch FMA that corresponds to the "pitch snapshot" maybe Peter knows. At least on the Atlas aircraft, it doesn't appear that LNAV and VNAV will remain with a master FMC failure or dual FMC failure. Hellowk's position is that LNAV and VNAV both have lines through them. We could use more input here.

I see, it shouldn't automatically change to HDG HOLD | V/S. It should internally use wings level and pitch hold; these modes are not the same as ATT | V/S, so this certainly means that LNAV/VNAV remain annunciated but with yellow lines.

The remaining question is whether the FMC selection for LNAV/VNAV is really automatic in case of an FMC failure. Perhaps Peter tried to say that it shouldn't change to HDG HOLD | V/S but it should keep LNAV/VNAV with the yellow line and with those wings level and pitch hold submodes engaged?

QuoteThe remaining question is whether the FMC selection for LNAV/VNAV is really automatic in case of an FMC failure. Perhaps Peter tried to say that it shouldn't change to HDG HOLD | V/S but it should keep LNAV/VNAV with the yellow line and with those wings level and pitch hold submodes engaged?

That sounds good to me. Maybe he can chime in.

My old engineering manuals don't specifically say what happens if there is a completely dead FMC. It just says if the Master FMC has failed an internal test, the non-Master will try to resync the Master. During this time, A/T mode shows blank, roll and pitch show mode fail [I assume yellow lines], with FD bars biased out of view, but a footnote says VNAV may change to altitude hold (ALT) if the airplane is near the MCP altitude. I assume LNAV remains with a yellow line, but the aircraft goes into some kind of roll submode to stop it flying erratically (wings level? track hold?). I'm not sure if the FD pitch bar remains in view if the A/P switches to ALT. The Upper EICAS shows >A/T DISC and >FMC MSG. The Master CDU display is frozen. The non-Master CDU shows SINGLE FMC OPERATION, then RESYNCING OTHER FMC with the MSG annunciator light illuminated.

If the resync fails (after 35 seconds), the Master CDU goes to the MENU page with the FAIL annunciator lighted. The EICAS message >FMC-L appears (not sure what happens to the A/T DISC or >FMC MSG). The pitch/roll indications remain the same.

If the non-Master becomes the Master (by manual switching), all the EICAS messages clear except the A/T DISC (cycle A/T the switch off/on). All the other indications are normal (including pitch/roll bars).

We had a LOFT scenario where a failure of the L FMC with the FMC master at LEFT occurred just after take-off with the Captain flying.
In this event the autothrottle would disengage as you have discussed because of the selector position. If it was the right FMC that failed in this case the autothrottle would have remained engaged as the FMC selector was to the left.

In this flight the left side NAV display would be useless without switching. The easy option is to simply hand over control to the co-pilot as he had a full display to save fiddling about at low level.

My understanding and experience is that the flight system does not go to basic modes with a single FMC failure. You have to have a double failure for this to happen. Nor will you get amber lines through the LNAV and VNAV annunciations. They will be normal. Remember that these are not "picture" switches like the NAV source selectors - they show the state that the aircraft is in - it doesn't matter if one or other FMC side has failed.

Peter

Thanks for the input, John.

Peter, when you say the flight system does not go to basic modes with a single FMC failure nor will you get amber lines through the LNAV and VNAV annunciations, does this mean the LNAV and VNAV will continue to be fully-functional without moving the FMC master switch to the operable FMC? So, like Hardy mentioned earlier, there is some automatic switching to the operable FMC in case the master FMC fails?

I'm wondering if this is some sort of option that can be set by the individual operator, since the Atlas material has the autopilot EICAS and the autopilot operating in a degraded mode with the failure of just the master FMC.

That is my understanding, Jon, yes.

The FMC selector decides which FMC gives guidance to the flight systems, as you know, so that both pilot displays show appropriate (and the same) guidance commands.

If there was no automatic changeover, then a failure of a single FMC (if it was the one selected) would cause failure of guidance on both sides. I am pretty sure that doesn't happen - it wouldn't seem safe to me to have a switching mechanism that caused that to happen?

I can't see how this could be an airline option myself...

I am in the big sim Friday and will try and fit in a single FMC failure and see what happens maybe?

Peter

Thanks, Peter. It would be great if you could try it in the sim this weekend and see if the AFDS actually follows the LNAV and VNAV. As you know, once a failed FMC is identified in the sim (you see the amber VTK), action is usually taken so promptly to select FLCH and HDG SEL that I don't know of anyone who has actually let it go to see whether LNAV and VNAV would actually contiue to work. It would also be interested to see if the BA sim gives you the AUTOPILOT EICAS for a failure of the master FMC.

I think, after the FMC failure event, it would be a good idea to wait at least 40 seconds and then see how LNAV/VNAV behave.


|-|ardy

Indeed, Jon. I will try and fit it in..

Here is my FCOM2 extract:
---------------
In flight, the scratchpad message SINGLE FMC OPERATION displays on only one CDU after loss of the FMC not selected on the FMC selector. The scratchpad message TIMEOUT - RESELECT displays on the CDU with the inoperative FMC.

In flight, the scratchpad message TIMEOUT - RESELECT displays on both CDUs after loss of the selected FMC. The FAIL light illuminates in all three CDUs. The navigation display with the NAV source selector selected to the failed FMC is lost. There is a time delay before the FMC message FMC LEFT, RIGHT displays. When the FMC selector is rotated to the operative FMC, the FMC is available through the CDU. Once an FMC page is accessed, the scratchpad message SINGLE FMC OPERATION displays on the CDU with the operative FMC.

Dual FMC Failure

If both FMCs fail, LNAV, VNAV, and autothrottle are not useable. The CDUs supply route data to their respective ND.
---------------

Of course a single FMC "hiccup" (temporary failure) in cruise is quite common, and it is possible for the system to do a kind of "software reset" which is additional to the outage - if this happens (and it is mentioned in the FCOM as an "if") then you will temporarily lose LNAV/VNAV etc until you reactivate the data.

Interestingly, I note that the 777 has a L/AUTO/R selector, and the QRH stipulates that if you have the switch in other than AUTO you will lose LNAV & VNAV if the selected side fails. The 747 of course does not have the AUTO option but then neither does it deal with loss of LNAV and VNAV in the QRH. Go figure..

And as Hardy says - it is best to sit on your hands for a bit! I don't remember going to basic modes as you mention, but then I don't remember a lot these days!

Peter

Quote from: Britjet on Tue, 16 Feb 2016 21:48
Here is my FCOM2 extract:
---------------
In flight, [...] TIMEOUT - RESELECT displays on the CDU with the inoperative FMC.

In flight, [...] TIMEOUT - RESELECT displays on both CDUs after loss of the selected FMC.

Is there a certain delay or an action between these two FCOM statements? Otherwise they're contradictory, aren't they?

Perhaps the definition of "loss of the selected FMC" reads: "FMC is inoperative for 30+ seconds".

Also, I don't understand why CDU C should illuminate its FAIL light; CDU C is never connected to an FMC. I thought the FAIL light illuminates on a CDU if that CDU is connected to a failed FMC via the NAV source selector. CDU C provides standby navigation and alternate nav radio when both FMCs have failed; so dual FMC failure is a state that CDU C knows, but why should its FAIL light illuminate for a single FMC failure?


|-|ardy

Quote from: BritjetMy understanding and experience is that the flight system does not go to basic modes with a single FMC failure. You have to have a double failure for this to happen. Nor will you get amber lines through the LNAV and VNAV annunciations. They will be normal. Remember that these are not "picture" switches like the NAV source selectors - they show the state that the aircraft is in - it doesn't matter if one or other FMC side has failed.

Quote from: HardyAlso, I don't understand why CDU C should illuminate its FAIL light;

My notes do say ALTN NAV RAD (including on the C CDU) should become available with both FMCs failed or if the master fails in flight, but there were some strange variations during some real world ground tests I did for you, Hardy.

QuoteInteresting. On an aircraft today, [on the ground with the IRUs in NAV], I pulled the Master FMC CB and got the following:

Capt: No <FMC prompt available on Menu, no NAV RAD at all, SNS(?) available.
F/O: All normal FMC functions ok (NAV RAD, etc). This doesn't make sense at all, because we are told that only the Master FMC can control radio tuning [and the wiring schematics show this].

With the IRUs off, both <FMC prompts not available. All alternate functions available.

Perhaps the definition of "flight" is IRUs in NAV?

As Hardy says, I would wait for at least 30~35 seconds and then look at what is available.

I can confirm that Peter's excerpt also shows up, verbatim, in a Polar Air Cargo FCOM from 2009. Unfortunately, it lists some of the indications you will see if an FMC fails, but it still doesn't describe what you will see on the FMA or whether LNAV and VNAV on the failed FMC (left in most cases) will continue to work without moving any switches.

https://drive.google.com/file/d/0B-WRh0Hf7VdZWktmakRwZThkM0U/view?usp=sharing

To quote from my FCOM:

FMC Failure
Single FMC Failure
After loss of a single FMC, a resynchronization may occur. The active route may
become inactive, the performance data may be lost, and LNAV and VNAV modes
may fail.

So yes Hardy, I'm having a yellow strikeout through my LNAV and VNAV. The QRH did not mentioned anything about the LNAV and VNAV though. So Peter, you were right at the QRH part. It just mentioned to select a operable FMC, reengage the autothrottle and select a operable FMC on the NAV source selector.
Emerydc8, I'm reading exactly what you are reading with the Polar Air FCOM.

Hopefuly Peter can clear this up for us this weekend.

Further to what I wrote earlier...

http://www.iinet.net.au/~b744er@ozemail.com.au/PSX/Resync.GIF

So, it's looking like amber lines through the LNAV and VNAV, but if close to the MCP altitude, VNAV goes to ALT? This "degraded" autopilot mode and AUTOPILOT EICAS piques my interest.

Hi Hellowk.

Absolutely true what you say - the emphasis of course being on "may" for each of the items. This happens if there is a software reset, which in itself may be the cause of the FMC failure in the first place, but by no means the only cause, hence the "may"...
Peter

In the current PSX version, the FMC malfunction on the Instructor provides these variations:

Severe: "Persistent power supply failure",
Non-severe: "Bubble-memory case temp exceeds 85°C, auto-shutdown"

This means in the non-severe variation the FMC will re-activate after some random generated minutes.

In the next PSX update I could change this variation to something like this:

"Non-severe: "Software reset and resynchronization in less than 30 seconds."

Would that be a more interesting variation?


|-|ardy

Yes, Hardy, that would be nice to have. Hopefully we can get more details about what exactly the FMA will show and what the AFDS does in the event of a single master FMC failure (e.g., does VNAV/LNAV continue to work or does it go to a degraded AFDS mode with an AUTOPILOT EICAS alert?).

Also, and this is a bit off-subject, Peter pointed out above that there is no checklist for loss of LNAV or VNAV. At my company, these failures are actually given more than a single FMC failure, probably because there is no annunciation -- You just have to recognize that LNAV or VNAV didn't go active when it should have.

My company likes to fail LNAV and VNAV on a heavy takeoff and give you an engine fire at rotation. Of course, they will do it on a runway with a special engine-out turn procedure too; so while you are loaded up trying to fly the procedure and dealing with the engine fire, they are hoping you forget to select CON thrust by the five-minute mark. You will usually recognize that VNAV has failed early-on when you are still looking at TOGA past 400', and you will probably have selected FLCH and set V2+100 at 1000'. But if you go one second over the five-minute mark with takeoff thrust still set (you forget to press THR), they fail the other three engines and you will eventually get the red screen of death. It's sadistic, but there's not much you can say because you've exceeded a limit on three engines.

They also like to fail VNAV on takeoff out of HKG where you are limited to 220 knots until established inbound to TD. We usually set a speed on the LEGS page at TD with an at-or-below altitude 220/7000B and just delete this once established inbound to TD. That way, VNAV keeps us from exceeding 220 knots. When VNAV fails on takeoff, our normal procedure is to select FLCH and set V2 + 100 at 1000' AGL. That's almost always more than 220 knots. We had a captain get busted back to FO for a year because he fell into this trap and didn't catch it until he was past 220 knots.

So, having the ability to fail LNAV and VNAV would be nice. I'm sure you have a lot on your to-do list right now and this is pretty low priority, but I thought I'd bring it to your attention that our sim has the option to fail LNAV and VNAV.

You can fail LNAV and VNAV already now in the existing PSX versions.

Just let both FMCs fail.

Or pull one of the probe heat CBs on P6-4 in row D.


|-|ardy

Thanks, Hardy. I'll have to try a random, dual FMC failure, if I can do that. It is a bit different because of the stealth way that just VNAV or LNAV can fail without any other warning (no EICAS or alerts and the FMC stays the same). I haven't done any dual FMC failures because the procedure calls for me to move two switches that are out of my view, unless I scroll down to the glare with my mouse. I'll check it out. Thanks again.

Hi Hardy,

By failing both FMC or the probe heat will no doubt give the same results of a LNAV and VNAV failure.
However, we will probably have to deal with the problems of a dual FMC failure or a HEAT P/S CAPT which are different issues that we have to handle separately.
PSX have been instrumental in helping me understand what kind of faults yield what kind of results.
And to add on to emerydc8, out of HKG 07L, engine failure at 200", followed by a HDG SEL failure. Company procedures require us to fly a engine out procedure. But with the HDG SEL failure, it adds on to their 'fun' ( our torture).
What I'm saying is if the failures can be isolated like just  LNAV failure, or VNAV failure or a HDG SEL failure, it enables us to recreate many possible scenarios for training purposes. It's easy for me to say here and I believe it would probably take tremendous time and effort to implement. But it would also meant that PSX would be even closer to what we deal with in the sims. And this would be my wish list!

In your company sim, can you activate just LNAV fault, just VNAV fault, just HDG SEL fault -- separately -- without getting any other faults?

If so, have they occured in real life and therefore have been added to the sim? (If they happened in real life, they're obviously plausible). Or have they been added just for sadistic fun? :-)

Well, I can imagine an MCP pushbutton may mechanically fail. But once a mode is engaged, it can be disengaged only by pushing another switch (in most cases). That other switch might get a short circuit or something?

Our check airmen haven't found the HDG SEL failure button (and that's a good thing).

When they fail LNAV or VNAV in our sim (ex-ANA), there is no indication. All that happens is LNAV or VNAV just never goes active when it should -- it either stays armed or it entirely disappears from the FMA. This was actually a regular failure they were giving to everyone on type rides, although I don't know if it has ever occured in real life.

Usually, they would give a VNAV failure on the missed approach to 31L in JFK, where there is a 1000' level-off. That is one of the few missed approaches where you would select VNAV at 400' to keep from blowing through the 1000' level-off. With a VNAV failure, it won't level off at 1000'.

I think the missed approach may have recently been changed and they have since deleted the 1000' level-off.

I have not experience a LNAV, VNAV isolated fault myself as compared to emerydc8. However I did experience the isolated HDG SEL fault without other faults. Probably they are trying to simulate like what u have said, a MCP push button may mechanically fail. And if it fails at a time when you needed it, things might can a little interesting.

Quote from: emerydc8 on Mon, 15 Feb 2016 22:20
Thanks. Peter would know.

Hmmm..thanks for the comment - but it appears I don't!

On the big sim have just given this a go...
FMC selector to L. LNAV/VNAV departure on a SID with left A/P engaged at 250ft. LEFT FMC fail at 800r.

Amber "strikeout" on LNAV and VNAV after a few seconds. Both CDUs blank with TIMEOUT RESELECT (as expected)
Flight system and A/P in what I take to be "attitude stabilising mode" although there is no FMA annunciation of this.
Autothrottle disengages. Captain ND remains blank until switched on the NAV source selector.

Selecting FDs OFF then ON gives HDG (or ATT, depending on bank angle) and V/S modes on the FMA, with LNAV and VNAV showing ARMED (buttons still pressed on the MCP).

Selecting "FMC R" causes LNAV and VNAV to reengage GREEN. Autothrottle can be re-engaged.

I tried it again with an FMC R selection and the indications are what would be expected as per FCOM2.

Sorry if I misled anyone - I seem to remember it differently but obviously not. The FCOM2 and the QRH are pretty useless at giving help on this.

HTH

Peter

Thank you, Peter!

What looks strange to me is your observation of LNAV | VNAV being armed and shown in white on the FMA while the FDs are OFF. Are you sure they didn't blank completely in this moment? Perhaps you re-armed them manually when HDG HOLD (or ATT) and V/S modes were re-engaged?

On the ground, before take-off, with both FDs off, can you arm LNAV and VNAV?


Cheers,

|-|ardy

Thanks Peter for the confirmation! Have been waiting eagerly for this.

Hi Hardy,

That is with the FDs back ON again..the LNAV and VNAV appear white armed..
I have suddenly thought that my training notes might have been dated back to my 777 days, which of course did have automatic switching. Doh!

Peter

Hi Peter,

and, when the FDs were on again, you pushed the LNAV/VNAV buttons, right? They didn't arm automatically. (Why, after a full FD reset, should the system arm them automatically?)


Cheers,

|-|ardy

Quote from: Britjet on Sat, 20 Feb 2016 14:38
Selecting FDs OFF then ON gives HDG (or ATT, depending on bank angle) and V/S modes on the FMA, with LNAV and VNAV showing ARMED (buttons still pressed on the MCP).

Thank you, Peter!

Quote from: Hardy(Why, after a full FD reset, should the system arm them automatically?)

Quote from: PeterSelecting FDs OFF then ON gives HDG (or ATT, depending on bank angle) and V/S modes on the FMA, with LNAV and VNAV showing ARMED (buttons still pressed on the MCP).

Selecting "FMC R" causes LNAV and VNAV to reengage GREEN. Autothrottle can be re-engaged.

Trying to understand what Peter is doing/seeing in the sim.

If the A/P loses FMC LNAV/VNAV, and the modes have lines through them on the PFD FMAs, do the LNAV/VNAV buttons on the MCP remain illuminated? (when in the default A/P stabilisation submode).

Normally, if you switch off the FDs in flight with no abnormalities, the A/P remains in the mode it was last in. i.e. no A/P disengagement (yes?)
If you cycle the FD switches with A/P already disengaged (in flight), the FD's go into HDG HOLD and V/S(yes?)

Quote from: PeterSelecting FDs OFF then ON gives HDG (or ATT, depending on bank angle) and V/S modes on the FMA, with LNAV and VNAV showing ARMED (buttons still pressed on the MCP).

So the FMA goes from LNAV/VNAV with yellow lines to what with the FD's off?

I thought the table I posted earlier was saying that everything returned to normal (GREEN LNAV/VNAV) with the other FMC selected (ok, something has to be done to re-engage the A/T).

Thanks
Rgds
JHW

When I was writing my comment, I was intuitively assuming the A/P was disengaged while the FD switch cycling engaged V/S etc.

I didn't touch the LNAV VNAV buttons on the MCP. They were either yellow strikeout on the green background, or white ARM, depending on the FMC master switch position. I moved it left and right several times to see the annunciation change.

I think the best thing is to see if I can get a video of it on Tuesday.

Peter

Quote from: Hardy Heinlin on Sun, 21 Feb 2016 00:48
Hi Peter,

and, when the FDs were on again, you pushed the LNAV/VNAV buttons, right? They didn't arm automatically. (Why, after a full FD reset, should the system arm them automatically?)

The autopilot was engaged throughout, so it wasn't a full reset....

Here's a video of last night's efforts on the big sim. Apologies for the poor quality, but I think it should clear things up.

Peter

https://youtu.be/Z54Z3P5WG04

Thank you, Peter. Very helpful.

The reason why you didn't get the LNAV/VNAV modes armed by cycling the FD switches: This was probably because you cycled FD R off-on, then FD L off-on (if I understood your video comments correctly). So there was no moment where both FDs were off at the same time.


Cheers,

|-|ardy

Hi Hardy

I think both FDs were off together at one stage..?
Peter

Aha, so it behaved different this time? I'll take this one as a reference :-)


|-|ardy

Yes, not sure what happened last time - maybe finger trouble..

Thanks again, Peter. So, you do get the AUTOPILOT EICAS in addition to AUTOTHROTTLE.

I guess we can add the lines through LNAV and VNAV in the list below, along with some other interesting indications, thanks to your video.

QuoteSymptoms of an FMC failure:
 EICAS: FMC LEFT/RIGHT.
 If the left FMC fails and the FMC master selector is on L:
 Autothrottle failure. EICAS: AUTOTHROTTLE.
 Autopilot operates in a degraded mode. Degraded autopilot mode (EICAS >AUTOPILOT) means roll is level
and pitch is the pitch snapshot at the time of failure. Pilot with an operating ND becomes the PF. Select HDG
hold and ALT hold on the MCP.
 The ND displays MAP and VTK (VNAV track). LNAV, and VNAV are not available. Heading select and FLCH
may be used if necessary.
 TIMEOUT-RESELECT and/or ND blank.

Interesting to see TERR POS on the Upper EICAS.  ??? Is this because the Captain's Map was not available? I noticed that when the R FMC was selected on the Captain's ISSM, the message didn't disappear (or is that because the message takes a few seconds to disappear?)

I see the A/P didn't go into ALT (green), despite the altitude agreeing with the MCP altitude.

I wonder what the Status message/s were.

Hi John

The status messages were there before the start of the experiment. I don't recall what they were..
Peter

Quote from: John H Watson on Tue, 16 Feb 2016 11:18
If the resync fails (after 35 seconds), the Master CDU goes to the MENU page with the FAIL annunciator lighted.

I tried to model this delayed appearance of the MENU and FAIL light. It's too complicated; it has too many risks and side effects in my model design. I leave this detail as it is: In PSX, the MENU and FAIL light appear during the resync already. Access to an FMC page is denied in any case, so it shouldn't confuse any student.


|-|

Is it true that the FAIL light illuminates on all three CDUs whenever the master FMC is inoperative?

Even if a CDU is linked with an operative FMC, the FAIL light illuminates on this CDU?


|-|

Quote from: John H Watson on Tue, 16 Feb 2016 11:18
... a footnote says VNAV may change to altitude hold (ALT) if the airplane is near the MCP altitude.

I assume this is true not only in the moment when the FMC failure occurs, but also during an already running "mode-fault-pitch-hold" climb or descent ...
• when the MCP ALT is captured
• or when you move the MCP ALT bug to the current altitude.

My reference for "near" is the +/- 50 feet width of the PFD tape bug.


|-|

Modifications are now implemented in 10.0.8-beta8:

http://aerowinx.com/board/index.php?topic=3462.0


|-|

Thanks, Hardy!

Thanks!

Hi Hardy,

Just downloaded your update.
Under the VNAV of the update, you mentioned this :
0.8.0039. Master FMC failure: If current altitude is more than 50 feet from MCP altitude, VNAV word gets amber line, and AFDS maintains pitch (unless in alpha protection); otherwise ALT mode engages.

However, I did not experience this in the SIM, VNAV will get a strikeout as well. I went through Peter's video and this is the case as well. Also, one of our instructor pilot had a write up on the failure and I will share the picture.
https://drive.google.com/file/d/0B8u4g8QNcHNPNFIxYmNSWU81OEU/view?usp=sharing

Regards,
Ray

Hi Ray,

I referred to this quote:

Quote from: John H Watson on Tue, 16 Feb 2016 11:18
During this time, A/T mode shows blank, roll and pitch show mode fail [I assume yellow lines], with FD bars biased out of view, but a footnote says VNAV may change to altitude hold (ALT) if the airplane is near the MCP altitude.

"May". -- Perhaps you may see this in your sim as well -- sometimes -- just not every time?

I don't know the conditions behind "may" ...

Maybe +/-50 ft is not the final condition?

Maybe it's similar to the V/S mode's altitude capture: ALT may engage only during vertical motion when coming from outside the ALT bug width of +/-50 ft? I think the faulty VNAV mode (pitch hold submode) is an AFDS mode (not an FMC mode) and therefore is able to capture the MCP altitude; it would be a bad design, in my opinion, if the pitch hold submode would shoot through the MCP ALT, although it is technically able to monitor it.


Regards,

|-|ardy

Hi,

in update 10.0.8 I implemented the stuff with the yellow lines through the LNAV/VNAV mode words etc. when the master FMC fails. In previous versions LNAV/VNAV changed to HDG HOLD/ALT etc. in this case.

This implementation has a side effect: Other relevant failures keep LNAV/VNAV now engaged and operative. In previous versions they too caused LNAV/VNAV to change to HDG HOLD/ALT etc.

These other relevant failures are:

• Less than 3 engines running
• IRS not aligned
• Any probe heat failure

I think these 3 conditions too should have the same effect on the LNAV/VNAV modes as a master FMC failure.

As usual, when any of these 3 failures exist, armed LNAV/VNAV cannot engage. That's OK. But once they are engaged they won't disengage anymore. That's not OK.


Regards,

|-|ardy

Hi Hardy,

I have been having a discussion with Jon recently that I seemed to recall that LNAV and VNAV didn't work with two engines failed. He quoted a colleague who tested it and said that they did work.
So you are saying that you think they should be inoperative?

Peter

Hi Peter,

well, if he tested it, then I believe him. I didn't remember that discussion.

I'll remove the E/O condition from those 3 criteria ...

What remains is the probe heat criterion (IRS alignment loss will disengage the whole AFDS anyway). I'm sure that this will inhibit the LNAV/VNAV engagement (real life incident, and QRH notes), so it must also disengage it, respectively draw that yellow line etc.


Cheers,

|-|ardy

I just re-discovered a source in an 744 FMC engineering book from 1989 which says VNAV will disconnect when "more than one engine failure is detected".

(Ref 6-123)

Hi Hardy and Peter,

I am 100% sure that Atlas has its pilots arm LNAV and VNAV on a 2-engine approach. They want you to wait until the VPP is 1000' low before turning your base. When you turn base, they want you to do the LVSA procedure (Arm LNAV, Arm VNVAV, Speed Intervene, Set Decision Alt). They use 500' as a nominal decision altitude. So, although you have no A/T, they still want you to use LNAV, VNAV and A/P to start the approach and then disconnect just prior to 1000' when you center the rudder trim.

Jon D.

Hi Jon,

that book from 1989 might be outdated.

If they want you to arm LNAV/VNAV, are you sure that they expect an engagement, and that they don't want to demonstrate any non-engagement?


|-|ardy

They definitely expect an engagement. The idea is that they take away your ILS and radar when you lose a second engine on your 3-engine missed approach. This leaves you with no lateral or vertical guidance and you are totally own your own trying to get back to the airport (no vectors either) You tell the NFP to select the ILS for the runway you want and extend from the runway fix (threshold). Even though there's no ILS, this gives you lateral and vertical guidance to the runway and it also activates the on-approach logic because you are within 25 miles of the threshold. When you are on a downwind, you turn your base when the VPP shows 1000' low (fly up), then do the LVSA and the AFDS will intercept the final and start down in VNAV PTH. At 1000', you disconnect the A/P and center the rudder trim, but you still have F/D guidance all the way down to the runway using VNAV and LNAV.

These are the check airman notes from last year:

 2 engines inoperative.
 Do not set the MCP below 500'.
 Back up the approach with an ILS if available. Use the glideslope if it is available.
 Visual approach techniques are encouraged and may be used if desired.
 If no ILS glideslope is available, use VNAV. Either of the following methods may be used and selected from the DEP/ARR page:
 A non-ILS approach. Preferred method.
 Any approach and extend the runway fix on the LEGS page. Alternative method.

I would say from my experience, I do seem to recall, that on the BA sim VNAV and LNAV are not available. Jon and I had a private email conversation about it recently)
Unlike Atlas - in BA we didn't try to make a very difficult situation even more difficult by removing ILS etc).
More intrigue!
Peter.

Thanks, Peter. I wonder if there was some rationale at BA behind intentionally disabling LNAV and VNAV when you lose two engines. Probably whoever might have made that decision is long retired/passed on by now.

On my type-ride, my airline was a bit nicer on the 2-engine approach -- They gave me vectors for the RNAV Y 04L at JFK. Like Atlas, they don't allow use of the ILS on a 2-engine approach. Instead of extending from the runway fix, as Atlas teaches, I had my FO extend from the FF. I'm not a big fan of using the A/P when down to 2 engines, so I hand flew the approach and I am 100% certain that the F/D gave me VNAV and LNAV guidance all the way down. So, the ex-ANA sim also allows LNAV/VNAV on a 2-engine approach.

If you pop an engine at say 30 West and it takes a second engine with it, when you select the E/O prompt, VNAV displays ACT 2 E/O LRC CRZ. We know the A/T wouldn't work on two engines, but why would Boeing not want you to at least have VNAV and LNAV in this situation? At least you wouldn't have to use HDG SEL in Class 2 airspace for several hours or use FLCH or V/S to maintain the D/D speed. On BA's oceanic contingency procedures for loss of two engines, was there any mention that LNAV and VNAV would not be available? 

Jon D.

Regarding any probe heat failure, we may need to revisit this thread

http://aerowinx.com/board/index.php?topic=3643.0

TAT, engine P2T2, etc, may or may not be similar.

Hi John,

Do you think the discrepancy between the BA sim and the Atlas/ANA sims (LNAV/VNAV availability with two engines inop) could have something to do with the engine type? RR v. GE?

Not sure. One of the differences between RR's and GE's, I recall, is that if any engine EEC is in Alternate mode on the RR, the A/T cannot be re-engaged. I assume any fault which creates EEC alternate mode would stop A/T engagement. I can't remember if (fuselage mounted) pitot/static probe heat faults cause EEC failures.

Hi Peter,

is there any chance to test in the BA sim whether LNAV/VNAV can be engaged if 2 engines are out? If it can't I need to add another airline option.


Hi Jon ...

QuoteACT 2 E/O LRC CRZ

I've never seen this page title in any books. I assume this was a software update. In the books I always read "E/O", and since this term doesn't say anything about the number of engines, I assumed it always means 1 E/O. On the other hand, the PSX FMC does automatically display lower MAX and OPT altitudes when more than one engine is out. It just doesn't indicate the number in the page title.

Now ... what if 3 engines are out? Can LNAV/VNAV still be engaged? It's certainly impossible when 4 engines are out because probe heat is then unavailable due to AC bus power loss.


|-|ardy

Hi Hardy,

I will try and do a test if I get chance. It will be a week or two..
Peter

QuoteDo you think the discrepancy between the BA sim and the Atlas/ANA sims (LNAV/VNAV availability with two engines inop) could have something to do with the engine type? RR v. GE?

Here are a few clues on how the RB211 EEC responds to probe heat failures (ref to link below):

If the engine "P2T2" probe heat fails it seems that the EEC switches automatically to Alternate mode irrespective of what the fuselage pitot-static probe heat is doing.

The aircraft has to validate the P2T2 probe data (generally) by comparing it with fuselage mounted probe data from 2 ADCs. If one fuselage pitot-static probe heat fails, I think the EEC has the chance to switch to the other fuselage pitot-static probe. If only one fuselage pitot-static probe heat fails, just one of the two EEC channels fails (i.e. no ALTN mode, I think)

http://www.iinet.net.au/~b744er@ozemail.com.au/PSX/ProbeHeatEECAlternate.GIF (http://www.iinet.net.au/~b744er@ozemail.com.au/PSX/ProbeHeatEECAlternate.GIF)

I don't know if the PW4000 follows these lines. The GE doesn't have a P2T2 probe because it uses N1 as the primary parameter.

Thanks for the info, John. I was thinking more along the lines of an engine failure and not a probe heat failure. The probe heat system is sounding as bad as the LLCCAFR system though!

Hi Hardy. The Atlas/Polar FCOM says:

QuoteIf a second engine fails, the page title changes to ACT 2 E/O LRC CRZ and the FMC calculates and displays two-engine out maximum/optimum altitudes and performance data.

Hi Peter,

Can you get your hands on the 3-engine ferry procedure for BA? Maybe it's something similar to ours.  It looks like VNAV will still work on our aircraft after a second engine fails.
Thanks,
Jon D.
(http://www.hoppie.nl/forum/var/3-eng-ferry-2-eng-out.jpg)

Hi Jon,

I just had a look through the current manual, and there is no checklist as such, and no mention of VNAV etc.
It merely says that in the event of a two-engine situation that the FMC will give two-engines inoperative data.

Just looking at your checklist - I am wondering if the page you show is talking about two separate things - the top section being about a further failure, and the bottom section being about handling the single failure...?
It almost looks like a poorly-placed cut-and-paste to me?

Peter

Hi Peter,

Yes, I see how it could be construed that way. It probably is a bad cut- and-paste job. I would note, though, that it doesn't say anything about VNAV not being available with a subsequent engine failure. I'll keep researching this. Thanks.

Jon

[ I moved the "one engine inoperative ferry" discussion to: http://aerowinx.com/board/index.php?topic=3697.0 ]

Hi Hardy,

I am revisiting this FMC failure issue, because I want to do a video on it. I just wanted to ask a few questions and, since Peter took his video down, I can't compare PSX with the big sim. In PSX, when the left (master) FMC fails during a VNAV climb, there is a time delay of about 30-seconds before the ND goes blank and the boxed MAP/VTK appears on the ND, followed about 10 seconds later by the right CDU going from RESYNCHING OTHER FMC to SINGLE FMC OPERATION, and then FMC L appears on the EICAS a few seconds after that. Does this duplicate the big sim? It has been so long since I saw his video I can't remember, and I recall that you were in the process of making some changes to PSX as a result of the video. Thanks.

Jon

The resync delay has been observed in the BA sim, I think, and agrees with the manuals. And the ND symbols and delays have been observed on the real aircraft on the ground, and agree with engineering manuals as well.


|-|ardy

Okay. I think I found the answers in John's chart below. After 35 seconds and no resync (and no pilot action), it goes to SINGLE FMC OPERATION followed by an EICAS FMC L. Is the RESYNCING and SINGLE FMC OPERATION reversed in John's chart? In one place, it says SINGLE FMC OPERATION then RESYNCING OTHER FMC for the right CDU scratchpad message.

I ask about the ND (VTK/MAP) delay because I know in our sim, there is no delay in displaying VTK after an FMC fail. In fact, they teach that this is usually the first sign of an FMC failure. I also noticed that the Bulfer book seems to support this (p.22.1 Jan. 1999). It would be nice to see the video again.

QuoteFMC FAIL
FMC FAIL and HSI MAP FAIL and VTK messages will be displayed continuously during the thirty second resynching process.

(http://www.hoppie.nl/forum/var/fmc-fail-chart.gif)

Quote from: emerydc8 on Tue,  6 Dec 2016 06:47
I ask about the ND (VTK/MAP) delay because I know in our sim, there is no delay in displaying VTK and MAP after an FMC fail. In fact, they teach that this is usually the first sign of an FMC failure. I also noticed that the Bulfer book seems to support this (p.22.1 Jan. 1999). It would be nice to see the video again.

I missed this detail, or something was different on the real aircraft. I can't remember.

I'll try to modify it this month ...

Thanks, Hardy.

As far as the message in the right CDU scratchpad, should it be like John's chart where it says SINGLE FMC OPERATION first and then RESYNCING OTHER FMC after that? It looks like the chart may be reversed. I don't remember if Peter got this part in his video.

They appear nearly at the same time, but RESYNCING OTHER FMC overwrites the other messages; it suppresses the SINGLE FMC OPERATION message, otherwise, during single FMC failure detection, you would never see the RESYNCING OTHER FMC message.

When RESYNCING OTHER FMC disappears from the message stack, the next message in the message history becomes visible, which in this case must be SINGLE FMC OPERATION for obvious reasons. As the single operation continues, this message can only be cleared by the CLR key. RESYNCING OTHER FMC cannot be cleared by the CLR key. It clears automatically when the resync attempt is done.

The chart agrees with PSX: In PSX, SINGLE FMC OPERATION is visible for ca. 2 seconds, then RESYNCING OTHER FMC appears which cannot be cleared (all FMC keys are inop). When the resync is done, RESYNCING OTHER FMC disappears. If there are still single FMC operation conditions, SINGLE FMC OPERATION re-appears (no longer overwritten by RESYNCING OTHER FMC).

Got it. Thanks! I missed the initial appearance of SINGLE FMC OPERATION.

I was just looking at the Smith FMS manual for the 737-900. I know they are different animals than the 744 but I thought it was interesting that VTK doesn't appear at the time the ND map blanks. I don't remember if the map blanked right away on our -400 sim, but I do remember seeing VTK immediately.

QuoteIf the annunciator is lit due to an FMC failure, the following additional indications are provided:
− Dual configuration:
− Right FMC fails:
• The VTK flag is displayed on right ND and the map is blanked after approximately 30 seconds.

If the annunciator is lit due to an FMC failure, the following additional indications are provided:
− Dual configuration:
− Right FMC fails:
• The VTK flag is displayed on right ND and the map is blanked after approximately 30 seconds.
• SINGLE FMC OPERATION message is displayed in both FMCS display scratchpad areas.
− Left FMC fails:
• The VTK flag is displayed on left ND and the map is blanked after approximately 30 seconds.
• The FMCS display FAIL annunciator is lit and FMC is displayed in the screen (CDU Only).
• The FMCS display displays the MENU page with the FMC prompt (LSK 1L) blanked (MCDU and FANS
MCDU).

We often have to reset the FMCs in the big sim after a lot of repositionings (the sim sometimes gets confused).
In this case, after pulling the relevant FMC CB, the Amber map indication on the ND takes quite a while to appear (probably 30 seconds), and only then do we reset the breaker. The sim engineers told me that unless you wait for the MAP message the thing hasn't totally shut down.
HTH.
I will see if I still have the video, but I had a clear out recently!
Peter.

Just to be clear: I won't remove the 30 sec delay for the MAP. I'll just remove the delay for the VTK flag and the active waypoint's ETA & DTG -- those will disappear immediately.

These 30 seconds refer to the volatile FMC memory (INIT REF stuff, i.e. POS REF, PERF etc.) and the volatile CDU memory (standby nav). The data will vanish after 30 seconds. (While the nonvolatile magnetic-bubble memory stores the databases and routes only).


|-|ardy

I think my memory is volatile and has quite a lot of bubbles...

QuoteJust to be clear: I won't remove the 30 sec delay for the MAP. I'll just remove the delay for the VTK flag and the active waypoint's ETA & DTG -- those will disappear immediately.

Thanks, Hardy. That would comport with John's chart above too. The VTK flag appears, plus the ETA and DTG for the active waypoint disappears. If there is no resync after 35 seconds, then you get the MAP flag. I presume that's when the map (magenta line) disappears too?

Peter, thanks for checking on the video. I hope you can find it.

Jon

Quote from: emerydc8 on Tue,  6 Dec 2016 19:04
I presume that's when the map (magenta line) disappears too?

Yes.

Thanks!

In PSX update 10.1.1, in case of an FMC failure, the amber VTK flag and the removal of the active waypoint's ETA and DTG will now occur after 1 second instead of 30 seconds:

http://aerowinx.com/board/index.php?topic=4020.0

(Refer to item 1.1.009.)


Regards,

|-|ardy

Thanks Hardy!

Jon