Waypoints speed restriction

[scandinavian13 5,192]

 

 

After I modified(lowered) speed of all these waypoints, on next attempt, the plane still flew too fast passing waypoints with higher than restricted(modified) speed(drag required prompt). My 737ngx FMC computing this approach right.

 

Did you modify these prior to, or during the descent, though?

 

If you modified the speeds to lower speeds during the descent, you may not be able to meet the speeds because the lower speeds would require an earlier T/D to accommodate the decel points that would be necessary.

 

This 777 FMC is not the NG FMC (as noted in the intro manual).  It's not going to predict and set your speeds like the NG does.

 

They're both behaving like the real plane behaves, so while the NGX is doing it "right," so is the LR/F.  It's just that the LR/F is a little more reliant on the human up front to do what he or she needs to do as well.

[sbieg 0]

Did you modify these prior to, or during the descent, though?

 

If you modified the speeds to lower speeds during the descent, you may not be able to meet the speeds because the lower speeds would require an earlier T/D to accommodate the decel points that would be necessary.

 

This 777 FMC is not the NG FMC (as noted in the intro manual).  It's not going to predict and set your speeds like the NG does.

 

They're both behaving like the real plane behaves, so while the NGX is doing it "right," so is the LR/F.  It's just that the LR/F is a little more reliant on the human up front to do what he or she needs to do as well.

Yes, I modified them way prior to T/D. I like to be more in control using intervention knobs, manual modification, controls, etc., but if you let VNAV continue approach, the plane will hit(despite speed restr.) FF point with speed about 200 knots. Why FMC doesn't follow my commands(restrictions) entered into it ? Hard to believe, the real plane will do that.

[scandinavian13 5,192]

 

 

Why FMC doesn't follow my commands(restrictions) entered into it ?

 

It does, but there are tons of factors going into this:

Are you allowing it to?

Are you preventing it by not adjusting your hardware?

---The default A/T Setting in your PMDG Setup menu is to allow the hardware to override the A/T at certain points, which could cause issues (particularly when using VNAV because it will drop to HOLD mode, which is a mode that allows hardware override).

Are you preventing it by not cancelling your speed intervention?

---I suspect not, but I figured I'd point it out.

[sbieg 0]

It does, but there are tons of factors going into this:

Are you allowing it to?

Are you preventing it by not adjusting your hardware?

---The default A/T Setting in your PMDG Setup menu is to allow the hardware to override the A/T at certain points, which could cause issues (particularly when using VNAV because it will drop to HOLD mode, which is a mode that allows hardware override).

Are you preventing it by not cancelling your speed intervention?

---I suspect not, but I figured I'd point it out.

Thanks for good advise. I set A/T manual override at" IN HOLD MODE ONLY". No idea, how to prevent it by not adjusting my hardware. Need more info., please.

[scandinavian13 5,192]

Thanks for good advise. I set A/T manual override at" IN HOLD MODE ONLY". No idea, how to prevent it by not adjusting my hardware. Need more info., please.

Good know. Basically, from prior to T/D, all the way to the runway, you should have your hardware throttle on the idle stops - all the way back - to prevent it from commanding a higher thrust level any time the A/T drops to HOLD mode. In the real aircraft, that mode allows the crew to manually adjust the throttle while A/T is still on. Prior to dropping to that mode, though, the thrust levers would be moved back to idle because they're driven by servos in the real thing. Yours aren't, which can cause problems if you don't manually do it (or change the setting so that A/T always overrides your hardware).

[sbieg 0]

Appreciate that, scandinavian13.

[Jeff H 63]

It may be glitch in my 777 FMC. Here is, how it's computing descent profile : KDFW- RNAV-RWY17C(last segment): BOSSI 240/6000A-3NM-PENNY 240/5000A-6NM-ZING 240/3000A-2NM-JIFFY 170/2300A-5NM-RW17C170/612. Obviously, no way to reduce speed by  70 knots within 2 nm when descending. After I modified(lowered) speed of all these waypoints, on next attempt, the plane still flew too fast passing waypoints with higher than restricted(modified) speed(drag required prompt). My 737ngx FMC computing this approach right.

Just a couple of points I'll make here.  And to preface, I do bring a real world mentality to this because this is, after all, a study sim, designed to closely replicate real world performance. 

First, those restrictions are just that, restrictions.  You can't fly faster but you most certainly can fly slower.  The speeds programed by the FMC are the limits proscribed by the approach procedure, not the speeds that you're supposed to fly them at.  Second, you're the PIC.  It's your responsibility to program the systems/fly the plane to meet the required profile.   At 240 KIAS it takes about 30 seconds to travel 2 miles so yes, you'll have trouble bleeding off 70 knots in that time.  So that being the case, you should be commanding a slower airspeed a lot earlier.  The last thing is, and this one's a biggie, always remember that the most important thing in aviation is the next thing.  You need to be ahead of the aircraft.  The FMC is working the way it's supposed to work.  If it's flying too fast at a waypoint, it's because it can't do what you programed it to do within the limits of its' programming.  At 7 mi out and 3000MSL, you should be at or pretty close to the FAF, if not past it by then, and should already be in your landing configuration.  As I said in my previous post, and others have said, you shouldn't even be in VNAV at that point.  Like I said earlier, you are the Pilot in Command.  If you aren't flying the plane, then you're just another passenger...all the way to the scene of the crash.  :wink:

Cheers!!

[sbieg 0]

Yes, I realized that and always try to be ahead of the aircraft, entering lower speed of waypoints set prior to FF(full landing configuration) one. The problem is, VNAV, regardless, still try to keep 180-200 knots up to FF, which is obviously wrongdoing. I'm simply forced to use speed intervention, when perform RNAV approach. Just want to know, it's normal for this PMDG plane, or there is a bug in my 777 FMC. Thanks.

[scandinavian13 5,192]

 

 

The problem is, VNAV, regardless, still try to keep 180-200 knots up to FF, which is obviously wrongdoing. I'm simply forced to use speed intervention, when perform RNAV approach. Just want to know, it's normal for this PMDG plane, or there is a bug in my 777 FMC.

 

As I mentioned earlier, this is not the NG.  The NGX will automatically step the speed back based on the schedule.  The 777 will not.

 

This is a real world behavior.

 

The tutorial explains this, and demonstrates it as well.  I'd suggest flying through it once to get a feel for how it should work.

[sbieg 0]

Yes, there is a clear guide in tutorial #1, page: FINAL APPROACH. Somehow I'd missed it before. Have my appreciation again. By the way, there is no Tutorial #2 in my package. Any idea, where can I find that?

[scandinavian13 5,192]

 

 

By the way, there is no Tutorial #2 in my package. Any idea, where can I find that?

 

It will come out with SP1, in a similar manner as the NGX, so, hopefully in a few weeks.

 

Disclaimer: That's not an official PMDG release date.  It is my own super-vague estimate.  "A few weeks" could also mean a few months...who knows...PMDG doesn't do release dates and so on.

[hopskip 253]

Disclaimer: That's not an official PMDG release date.  It is my own super-vague estimate.  "A few weeks" could also mean a few months...who knows...PMDG doesn't do release dates and so on.

 

It will be ready in a few Units of Time and Date measurement.