VNAV still not working properly

[clayton4115 56]

thanks Dave that will be good.

[baw716 0]

Clayton and all,I have spoken to one line pilot (I am waiting to hear from the other); that said, the following is what I have been told:First, he believes, as do I after having spoken to him and have heard from another pilot (on this forum), that it is better to NOT take the runway with either LNAV or VNAV armed. HDG SEL and SPD/FLCH are the MCP modes of choice when on initial takeoff. HDG SEL and SPD/FLCH are activated at/above 400 feet, then there is differing thought on when VNAV is engaged; however, I am pretty certain both pilots agree that VNAV is not activated until after flap retraction is complete and the airplane is in a clean configuration. From there, VNAV can be initiated to your initial climb altitude as given to you by ATC, or you can continue with SPD/FLCH until above 10000, then engage VNAV climb above that. BIG NOTE: Continental's procedures are radically different: CO indicates to arm LNAV/VNAV on the ground prior to taking the runway and they will automatically engage after 400 feet.When I described that to my brother in law (the line pilot here), he said that while that was a procedure he had heard of (arming LNAV/VNAV on the ground), it was not a procedure that his airline used, as they did not want any computer intervention in control until the aircraft was above 400ft (in cases of engine out, etc.).Now, in the real world, the scenario you describe would not occur, where an inadvertent flap extention would occur (unless uncommanded on fly by wire aircraft) which to his knowledge has not occured.Now, my question, when you extended and retracted the flaps, did you reset the MCP altitude before hitting VNAV? One possibility is if there is a safety built into VNAV that kicks out on flap extension in the climb, resetting the MCP altitude should reset the computer. Give that a try, see if VNAV recovers after that. I am going to attempt to repeat the scenario you described, but I need to know one point: at what point in the climb and at what speed did you accidently extend the flaps? For me to recreate your scenario, I need that info, plus your TOW (ZFW plus fuel would be better).I am waiting for the other pilot I wrote to respond, then we'll have two opinions, which (when talking to line pilots) is always a good idea. Simply stated, each one from different airlines have a slightly different perspective and opinions about how the aircraft should be flown on departure. Therefore, take what information I am giving you now as an indication that there MIGHT be a problem with VNAV; however, I need to reproduce the fault myself before I can agree that it might be a PSS issue.For sure extending the flaps accidently is a bad thing. If you are using CH Throttle (axis vs. button for flaps), you may want to put a little more null zone in the flap handle, so if you accidently bump it, it won't do something.In the meantime, let's see if I can reproduce your incident.News at 11.All the best,Dave

[FOD 23]

DaveIf you check my earlier thread on this, I think you will find TOW etc are irrelevant. If you do a normal departure - as per the tutorial - engaging ap with VNAV and LNAV at 400ft; clean the aircraft up, then once in ACT 250 KT CLB mode select then retract 1 flap. You will see that VNAV does not kick out, the VNAV mode simply changes and the aircraft will start a gentle descent. We then found it impossible to recover the correct VNAV mode.Interesting to see the fairly significant differences between real life airline operating procedures.Also appreciate that dropping flaps like this is something you should avoid - as I said earlier - its a pilot pigs. Remember the old adage when you are looking at the way pilots work - "if something can be done - it will be done"Look forward to hearing how you get on.John R

[clayton4115 56]

hi Davethanks for your private email message to me, i sure will reply in the next few days as we are closing in on the Easter break here and i will have some spare time,i think John is quite correct in that the fuel onboard in irrelevant, however from memory i was quite heavy on takeoff with 70% fuel on board.I was at approximately 1000' and climbing when i accidently pressed the wrong F number on my keyboard which was assigned to FLAP DOWN, i was climbing and passed FLAP 10 on my way to FLAP 5 when i accidently pressed for FLAP down, then VNAV stopped working and the plane continued to descend gently at approx 1500 fpm, in order to regain altitude i had to go from VNAV to V/S and i dialled in 2500fpm on the MCP for it to climb, however i never ever regained VNAV until the plane leveled at her cruising altitude of 31000' which i set initially on the MCP before takeoff (which i never interfered with after that)hope this helps.p.s if you have the PMDG 737 it would be interesting to see if this happens / doesnt happen with this ac, but i still believe its a flaw in the PSS AC.rgds

[baw716 0]

This is a difficult post to write, since I am most probably going to get flamed for it. However after having spoken to two pilots (one a retired 777 Captain and instructor and the other a current 747 line pilot who has over 10000hrs on glass), having tested the question three independent times with the same result each time, I can find no problem with the operation of the VNAV on this aircraft. Given that fact, I must conclude that there are a number of reasons for the complaints by others on this subject: 1) Lack of experience and inability to distinguish the different modes in the MCP/FMC and 2) Possible computer space problems and or lack of memory which could affect the operation of the systems and 3) problems with removing and reinstalling the software, which many people have done, up to and including the draconian step of wiping the hard drive clean and reloading FS9 and the 777 again.The problem is most definitely not with the aircraft, at least as far as the VNAV question goes.The PSS 777 most definitely is set up for on ground arming of the LNAV/VNAV modes with engagement above 400 feet with autopilot arming very soon thereafter. I flew three trips, exactly the same loop and commanded flap extension after flap extension in the climb nearly up to the max flap extension speed in VNAV on autopilot. The worse that occured was a flattening of the climb and a loss in airspeed. At no time did I lose control of the aircraft, either in autopilot VNAV or in the FD mode. Therefore, I could not repeat the error caused by the autoflight system as stated by Clayton in his earlier post...and I tried several times.It is important to note that I do not doubt his word, nor that his failure was real. However, I could not get the aircraft to repeat the error; there was not even any annunciation change in the FMA.The same issue exists with frame rates. People claim that it is the aircraft, I was able to prove definitively that it was not, at least on my machine. Even the minor things I thought were potential bugs were issues with my own flying technique and not the aircraft itself.I will make a separate post describing the techniques described to me for use of the FMC/MCP on the 777, especially using VNAV mode. Everybody's opinions are as different as the way each aircraft is made for each airline...the procedures are a little different.I did find the aircraft not providing the correct progress time at destination, but this was an intermittent problem. This did not occur on every flight. There are some vaguerities with the 777 FMC than with some of the others; notably the severe difficulty in removing DISCOs. This issue is present on the real 777 FMC. How you program the FMC will determine if you have a disco in the setup.So, I wish to suggest the following to all virtual pilots:a) I strongly urge you to get a book on the 777/747 FMC. Since they are, for practical purposes virtually the same, if you get Mike Ray's 747-400 Sim Guide or Bill Bulfer's FMC Guide for Big Boeings, the information needed to learn to operate this complex computer is there. :( Read the PSS support documentation carefully. Really carefully. The answers to some of these questions are in the documentation.c) Clean your computers. This is especially important if you have a small hard drive (less than 100GB) with more than 60% of the drive full. I promise you that this aircraft will give you headaches if your computer does not run efficiently. It uses a lot of resources. It does so because of the complexity of the FDE setup and the modeling of the autoflight system. If you have less than 1GB of RAM, this aircraft will not operate properly. You need at least 2GB of RAM.Getting rid of the spyware, bad registry entries and defragging your computer daily, and I mean daily, will make a huge difference in the performance of your aircraft.d) BE PATIENT. It takes time to learn this beast. I am getting more proficient with it every day, but it is VERY different than flying the Level D 767-300, with which I am intimately familiar. Use the tutorials and if you don't belong to a VA, you may want to consider joining, since some of these VAs have both programmers and pilots, and they are able to help you learn to fly the aircraft and work through its unique quirks. This bird has quirks...this is for sure. However, it isn't broken.I wish I could say that there still is a flaw in this aircraft. It's an easy answer; but it would not be the right answer. I have yet to find a problem that I have been able to produce more than once. This tells me that it is more my flying than the program or aircraft. I know this because the more I fly the aircraft, the less problems there are, which tells me that I am getting more proficient with its operation.Please take some time to read through the material and get some pilot advice. I think that is a better use of our time than to sit here and claim something is wrong with the product when it clearly is not the case. It used to be...and we've gotten used to whining about it. Well, the bird flies really well now and I for one am satisfied that it works as advertised.I wish all of you success in learning to operate this complex and fantastic aircraft. Once you have your arms around it, I think you will be very surprised what this aircraft can really do.My best to you all,Dave LambCat IV Senior Captain B767-300United Virtual Airlines

[FOD 23]

DaveA very comprehensive post and I think we can now really get into this interesting oddity.Firstly, as to the three items in your first para, I do not think any apply - unless we can figure out what I am doing wrong in terms of "inability to distinguish .......".Next, did you consult your 777 pilots about the affect of lowering flap when settled in a VNAV climb mode?I could not find the max flap extension speed in the manuals but, by trial and error, it appears that to be from 260 ts at 2000 ft to about 270 kts at 30000+ ft. Above this speed there is a built in limiter which prevents the flap travelling even if selected in error. In this case, there is no problem - if the flaps do not actually travel, the FMC and VNAV mode do not change. So we are only interested in the speed range below 265 kts.Perhaps we can continue to compare notes to try and see what Clayton and I are doing.BTW, I am running two systems - one my main FS9 with all the add-ons, the second with a clean installation of FS9 with only the PSS 777 added. They are totally separate, both AMD driven but otherwise different hardware - they even have different version of XP. The following applies and is reproduced in flights on both systems.I fly a departure iaw the tutorial - Fd 0n and VNAV and LNAV armed before I start the roll. Gear up first at a safe height, then select AP at 400 ft and raise the flaps in accordance with the schedule on the PFD. This is what I see in the various VNAV modes:ACT LIM SPD CLB - whislt retracting the flaps - changes in flap selection make no differenceACT 240 KT Clb - once flaps are up above about 200 kts - any selection of flap results in the VNAV climb mode reading LIM SPD CLB and the FMC being commanded into ACT LIM SPD DES mode and it is impossible to recover to the required VNAV climb mode.ACT ECON CLIMB - again selection of flap below the limiting speed leads to the FMC being commanded into ACT LIM SPD DESACT ECON CRZ - now FMC is commanded into ACT LIM SPD CRZ with flap down; reverts to ACT ECON CRZ when flap retracted - as expected!ACT ECON CRZ DES - now is commanded to ACT LIM SPD CRZ DES with flap down; reverts to previous when flap retracted - as expected!etc etcThe FMC normal logic appears to be that if flaps are moved from up to any down selection - I emphasise "moved" - the VNAV mode changes to a LIM SPD mode in order to allow for the reduced speed necessary with flap. In all modes except the climb mode - for me - the LIM SPD mode allows the aircraft to carry on with the correct FMC profile - either CRZ, CRZ CLB or DES. But in CLB mode the FMC is changed to LIM SPD DES and CLB mode cannot be recovered even when flaps are retracted.Grateful if you would look again at the procedure I am using compared to yours and also at exactly what you see on a normal departure say in the 240 kt climb mode if the you extend the flaps to flaps 1.Certainly what Clayton and I get in the climb mode is totally illogical - I believe that it must be "finger trouble" on our part as it occurs on different systems with different 777 installations!Look forward to hearing from you.John

[baw716 0]

John and all,I want to respond to your post, but I will do so in pieces, since I wan to address each of your questions individually.>Firstly, as to the three items in your first para, I do not>think any apply - unless we can figure out what I am doing>wrong in terms of "inability to distinguish .......".On this point I respectfully disagree. It was a general statement and given as a possibility, not as something that applies to everyone. I am saying that there appear to be some procedural errors that some people are not recognizing. The second and third parts of that paragraph speak for themselves.>Next, did you consult your 777 pilots about the affect of>lowering flap when settled in a VNAV climb mode?Yes, in fact, we had extensive discussions on this point. First, we had to get past the fact that both of them stated that this would not happen in normal operations. This was a big hurdle to climb. Once I got them onto the theorical possibility did we start to get to procedurally what to do and also, what to check, both on the FMA and the MCP. Their point (and both of them said essentially the same thing), IF an uncommanded flap extension were to occur in VNAV CLB, it would take the aircraft out of VNAV mode entirely. It would continue flying the same profile (ROC and speed) that the extension would have created. In no case did they say that a flap extension would cause the nose to sink. It would fly v/s and IAS, even if not annunciated on the MCP or FMA.The big question that they had for me that I could not really answer was what was annuciated on the FMA when the flap extension occured. When I performed this action three times at different speeds, there was NO change in the FMA, but there was a perceptable change in the climb rate. The procedure given for this was a) engage FLCH to maintain speed for the altitude set while retracting the flaps. Once flap retraction was complete, reset the MCP altitude and reengage VNAV. I did that and I was able to recover the climb back into the VNAV mode I was in; cross checked against the FMC.>I could not find the max flap extension speed in the manuals>but, by trial and error, it appears that to be from 260 ts at>2000 ft to about 270 kts at 30000+ ft. Above this speed there>is a built in limiter which prevents the flap travelling even>if selected in error. In this case, there is no problem - if>the flaps do not actually travel, the FMC and VNAV mode do not>change. So we are only interested in the speed range below>265 kts. The max flap extension speed is based on the flap setting, but in round figures, 250kts is about the limit.>Perhaps we can continue to compare notes to try and see what>Clayton and I are doing.>BTW, I am running two systems - one my main FS9 with all the>add-ons, the second with a clean installation of FS9 with only>the PSS 777 added. They are totally separate, both AMD driven>but otherwise different hardware - they even have different>version of XP. The following applies and is reproduced in>flights on both systems.I presume that you are not running these with WideFS linking the two. This would cause software conflicts all over the place.>I fly a departure iaw the tutorial - Fd 0n and VNAV and LNAV>armed before I start the roll. Gear up first at a safe>height, then select AP at 400 ft and raise the flaps in>accordance with the schedule on the PFD. This is what I see>in the various VNAV modes:>ACT LIM SPD CLB - whislt retracting the flaps - changes in>flap selection make no difference>>ACT 240 KT Clb - once flaps are up above about 200 kts - any>selection of flap results in the VNAV climb mode reading LIM>SPD CLB and the FMC being commanded into ACT LIM SPD DES mode>and it is impossible to recover to the required VNAV climb>mode.>>ACT ECON CLIMB - again selection of flap below the limiting>speed leads to the FMC being commanded into ACT LIM SPD DES>>ACT ECON CRZ - now FMC is commanded into ACT LIM SPD CRZ with>flap down; reverts to ACT ECON CRZ when flap retracted - as>expected!>>ACT ECON CRZ DES - now is commanded to ACT LIM SPD CRZ DES>with flap down; reverts to previous when flap retracted - as>expected!I think you have found the key in your first statement and why, perhaps I was unable to reproduce the fault in VNAV: If the flaps cause speed loss below the minimum speed for this VNAV mode (act 240kt CLB), it will kick the VNAV out of climb mode. I must stress that this is based on a theory, since neither pilot would accept as a possibility flaps could be inadvertently extended (note: This is a Boeing issue...Airbus is different because the flap handles are different). I also wasn't watching the FMC in the climb; my eyes are on the PFD and the MCP...looking at the FMC is impossible for me to do without loss of situational awareness.I retracted flaps both below and above 200kts. I did get a change in the VNAV SPD box, the rectangle disappeared. However, when I reset the MCP altitude and reengaged VNAV, both below and above 200kts, I was able to reestablish the rate of climb, so I am struggling with the fact that you were not able to reset the VNAV, unless you did NOT reset the MCP altitude (this is the key).>The FMC normal logic appears to be that if flaps are moved>from up to any down selection - I emphasise "moved" - the VNAV>mode changes to a LIM SPD mode in order to allow for the>reduced speed necessary with flap. In all modes except the>climb mode - for me - the LIM SPD mode allows the aircraft to>carry on with the correct FMC profile - either CRZ, CRZ CLB or>DES. But in CLB mode the FMC is changed to LIM SPD DES and>CLB mode cannot be recovered even when flaps are retracted.According to the pilots I spoke to, your assertion is not correct. Remember, the MCP controls the flying and if there are conflicts, it will kick you out of a particular mode (VNAV) and put you into the safest mode-V/S based on the result of the impact of the flap retraction, plus SPD. However, it may not be annunciated on the MCP.Key question: Did you reset the MCP altitude (not for the same altitude, but for say, 500 feet below your assigned altitude)?>Grateful if you would look again at the procedure I am using>compared to yours and also at exactly what you see on a normal>departure say in the 240 kt climb mode if the you extend the>flaps to flaps 1.This is the place where there was a marked difference of opinion based on their own airline's policy regarding the use of the MCP/FMC in VNAV mode. Neither pilot advocated the use of VNAV armed on the ground. There are issues managing speed with VNAV engaged, since it is based on a specific climb profile as set in the FMC. If an engine goes out at, say 300ft and VNAV kicks in, it would be necessary to change from VNAV to some other setting, FLCH, for example, and this is a dangerous procedure to execute in a one engine out situation, since the procedure is gear, speed, MSA, then engage automatics once positive control is established.For your information, both pilots like to stay on the FD until above MSA using FLCH as their climb mode of choice. HDG SEL or LNAV above 400ft is less of an issue, since it is directional and if the aircraft is not on autopilot, it will continue on the track flown after takeoff until some pilot intervention is made. Both pilots told me the following:HDG SEL or LNAV is armed NOT on the ground, but 400ft above. When TOGA is pushed, the aircraft is locked to track once airborne, then HDGSEL or LNAV is engaged above 400 feet, then FLCH to the altitude set in the MCP. This maintains positive speed control as FLCH is predicated on speed first, then climb.Therefore, I am having difficulty getting to my "own" procedure, since there are so many variations on it. Certainly the logic given to me by these pilots is sound; don't put the aircraft into a situation in which you have to disengage a/p to correct it.>Certainly what Clayton and I get in the climb mode is totally>illogical - I believe that it must be "finger trouble" on our>part as it occurs on different systems with different 777>installations!This speaks to my point exactly. Hit the wrong button and things go awry...My next post will contain the exact procedure as spelled out in Mike Ray's sim guide. Look for it in a originating post.Kind regards,Dave Lamb

[FOD 23]

Dave'A very interesting summary and I need to read this very carefully tomorrow - my time zone at present is zulu+1 - to digest the details.However, I would be grateful if you would please look at the FMC CDU - that is where we are seeing the problem. Its not too hard as you are in AP and well clear of the ground - and this is a simulator. I use 2D panel for this kind of testing.The change to VNAV mode that we are seeing happens instantly the flaps start to move - it does not wait until the speed drops below 240 kts. Indeed it will happen at any speed after 240 kt climb mode is engaged - at about 205 kts - until the flap limiting speed. Basically, lower the flaps in this speed bracket and see what happens to the VNAV mode.Your key question - I have tried re-setting the MCP, it made no difference. And this is where the system we see is wrong - when the FMC mode changes it commands the AP to put the aircraft into a descent - ACT LIM SPD DES - although the MCP is still requiring a climb!Look forward to reading in more detail tomorrow and hearing what happens to yout FMC mode.RegardsJohn

[baw716 0]

John,I am -7UTC, so it will be well into the evening for you before you have an answer...but I will do this using the FMC and see what happens.Please read my post about VNAV Challenges. It will be finished around 0900UTC.This should give you some idea as to the complexity of the VNAV problem, and a reason why a great many pilots do not use it close to the ground.Best regards,Dave

[FOD 23]

DaveYour latest "VNAV Challenges" is a great exposition on the options. But don't forget that there are probably as many ways of doing things as there are pilots! More on this and the use of the FMC "for real" later, I will only say that to date I have had no problems whatsoever with the PSS/Boeing VNAV in normal operation.However, the basic questions as far as this thread is concerned is how the PSS VNAV is programmed in the case of a flap selection below max flap extension speed:1. Is the very different operation - as compared to that in CRZ and DES modes - which Clayton and I see in VNAV CLB mode common to all users?2. If so, is this the way PSS intended the FMC to be programmed?2.1. If so, it is not a bug - but I think that PSS should consider a change for the 757 as it is neither logical nor fail-safe! It should be programmed as with the CRZ and DES modes which are efective, totally safe and allow the aircraft to complete its planned FMC route using VNAV when required. 2.2 If not, it is a bug - admittedly very minor.Finally, one comment on the "Challenges" thread relevant to this one. If what you say at I.f is correct, the VNAV should move to a CRZ mode - not DES - and then the PSS VNAV programming would be wrong in its reaction in all other modes.Look forward to seeing your experience of testing this.RegardsJohn R