incredibly steep decents and space shuttle take offs

[scandinavian13 5,192]

I am sorry, but I have to disagree. That part is only true with VNAV SPD. VNAV PTH will maintain path, and either add thrust or request drag if speed varies too much from expected.FCOMv2 page 4.10.6 (190)I am not able to find a statement that clearly states that VNAV PTH is default descent mode, but this statement from page 11.31.27 supports it.11.31.32 also supports that.

I was about to address your comment as I see where you're coming from but it's been addressed by Ryan. PTH is really only used in the case you need a geometric descent (Cross point A at X and then cross point B at Y). Either way, even in PTH, there's still a big component of idle and pitch for speed, which is hugely affected by the CI in that portion.

VNAV SPD = pitch for speed with constant thrust setting (climb N1 limit or idle in descents) - always. There was a comment earlier about it not following the path well in VNAV SPD. There's a reason for this - it isn't trying to follow it at all. VNAV SPD is a completely different mode from PTH.VNAV PTH = idle thrust from T/D to first waypoint using pitch to meet the econ speed (which the idle path is calculated with), after the first waypoint, it goes into power-on geometric descent (you'll see the A/T mode go from ARM to FMC SPD). If you drop too far below the target speed, even in the idle PTH mode, it will add thrust to get you back up to target and then retard to idle again.

[Paul Deemer 13]

My flight today for United required 26,000 lbs Fuel, 12,900 lbs Cargo, and 133 Pax. I used De-rated takeoff, and Clb2 and it worked perfectly and switched over to Clb1 at the appropriate time. So for those of you that are flying light. Use Derate and Clb2 and your Rocket issues will go away.Update on this flight: With a cost index of 36 max descent rate 2800 fpm. Average descent rate 1800-2000 fpm.

[bamboofats 0]

Sorry, this is either an illusion because of what you're seeing visually or there actually are slight accelerations happening that let you know about it. Certainly you feel the onset of the descent, because that's an acceleration.Think about how you're standing on the earth right now with respect to "up" at the north pole. Very likely you're actually standing "sideways", the degree to which depends on your latitude. Do you feel this? No. Same idea here. At 1G, you cannot discern things like this - it's fundamental physics. Check out Einstein's "equivalence principle" and the part of Special Relativity about objects in motion at a constant velocity.Also - a descent at a high IAS/Mach is going to produce a higher rate of descent at a given angle than a slower one will over the same distance. You could be descending at 4000-6000FPM up in the higher altitude portion of the descent and it won't look like much at all out the window as far as the angle you're seeing due to the speed involved. Flightaware themselves btw say not to trust their data for speed, V/S etc - it's interpolation off the radar, slant range and all of that comes into it and it's just not accurate.

It is not entirely correct to say that in the presence of 1G, and without looking out of the window, the passenger cannot feel any difference between a high and low descent rate.Although the passenger is not experiencing any acceleration because of the constant descent speed, one can still tell a difference because of proprioception, how the body senses one's orientation in space.(via ear fluids and body contact forces) It is like on earth, where your G forces is 1, you can tell the difference sitting on a chair normally, and sitting on a tilted chair, blindfolded. The reaction to weight, from the chair onto the body, is applied on different parts of the body, For instance, standing up and lying down, the reaction to weight from the floor is acting on the feet and back respectively and the body can sense this.In the aircraft descending at 2 different, but constant descent rates, will need a different descent angle. This angle is like tilting the chair while you are on earth, although the effect may be less dramatic than G force changes with changing descent rate, but i believe one can still sense it if the angle is large enough. One extreme example is a pilot which decides to descent vertically straight down, unaccelerated(due to air resistance). The G force on the passenger is still 1G, but he can definitely sense something is wrong, as the reaction to weight on his body is not from the chair, but from his harness that prevents him from falling onto the seat in front.Marcus Jian

[Paul_Smith 92]

Here in Europe our low cost boys (easyJet, Ryanair) would simply cancel the flight! Iain Smith

Variations on this has been said a couple of times by different people but it is simply not true. The fact that there are no passengers on the 3:00 flight from Dublin to Newcastle does not alter the fact that the airframe and crew is needed in Newcastle at 4:15 to load for the 4:40 to Faro.

[Guest]

It is not entirely correct to say that in the presence of 1G, and without looking out of the window, the passenger cannot feel any difference between a high and low descent rate.Although the passenger is not experiencing any acceleration because of the constant descent speed, one can still tell a difference because of proprioception, how the body senses one's orientation in space.(via ear fluids and body contact forces) It is like on earth, where your G forces is 1, you can tell the difference sitting on a chair normally, and sitting on a tilted chair, blindfolded. The reaction to weight, from the chair onto the body, is applied on different parts of the body, For instance, standing up and lying down, the reaction to weight from the floor is acting on the feet and back respectively and the body can sense this.In the aircraft descending at 2 different, but constant descent rates, will need a different descent angle. This angle is like tilting the chair while you are on earth, although the effect may be less dramatic than G force changes with changing descent rate, but i believe one can still sense it if the angle is large enough. One extreme example is a pilot which decides to descent vertically straight down, unaccelerated(due to air resistance). The G force on the passenger is still 1G, but he can definitely sense something is wrong, as the reaction to weight on his body is not from the chair, but from his harness that prevents him from falling onto the seat in front.Marcus Jian

Agreeing with you I have to add that not all the persons react the same.I mean, someone has stronger and precise feelings ( f.i. motor biker pilots ) others could go in a huge roller coaster and feel like lazing about in front of the tv.

[Fabo 213]

Paul, good point about the pitch/tilt sensation, however, there is a difference still. pitch angle is of course dependent on descent rate, but only by the way of corelation of speed and AoA. Therefore you can descent with the same pitch, say, zero, as you use in level flight, but you need to either change the IAS, or, alternatively, change the properties of the wing. (this would be nicely demonstrated if we had a L1011 add-on with properly working direct lift control - hint hint nudge nudge PMDG? :) - that will keep the same pitch of 7° on approach disregarding the speed and vertical speed, by way of spoiler extension)Kyle, I say we agree to disagree. Sounds good?

[bamboofats 0]

Yes, if the aircraft is not accelerating (not changing speed or rotating), the effect is from pitch. So a higher descent rate paired with just the right increased airspeed would provide no change in the sensation as pitch is kept the same, ignoring increased vibrations etc. But this effect isnt significant for passengers as the different descent rates just mean a pitch angle difference of a few degrees, not easily noticeable. The G forces is the significant sensation felt, when aircraft changes speed, rotation. But still, I think it is incorrect to say that the pitch is transparent to the passenger, from a physics point of view.Marcus Jian

[scandinavian13 5,192]

Kyle, I say we agree to disagree. Sounds good?

Sure, but disagreeing isn't going to change how the aircraft operates, inherently.

[kabekew 0]

I've brought these ridiculous climb/descent rates up before in other threads and PMDG just doesn't want to hear it. They go off of Boeing test flight videos with zero passengers and cargo which show 7000fpm climbs and apparently that's what they base their VNAV code off. But in the real world it's just not like that and I wish they'd consider all this feedback from real world pilots and controllers who work with this aircraft this every day. The VNAV behavior just isn't realistic.And those who say 6000fpm isn't felt any different than 1000fpm? Actually yes it is, because eventually you have to pull out of that 6000fpm dive! And it's going to be felt a lot harder or a lot longer than pulling out of 2000fpm. You can't escape physics. Likewise with the negative g part when you push down into the steeper dive. That's what makes pax vomit.

[kevinh 409]

I've brought these ridiculous climb/descent rates up before in other threads and PMDG just doesn't want to hear it. They go off of Boeing test flight videos with zero passengers and cargo which show 7000fpm climbs and apparently that's what they base their VNAV code off. But in the real world it's just not like that and I wish they'd consider all this feedback from real world pilots and controllers who work with this aircraft this every day. The VNAV behavior just isn't realistic.And those who say 6000fpm isn't felt any different than 1000fpm? Actually yes it is, because eventually you have to pull out of that 6000fpm dive! And it's going to be felt a lot harder or a lot longer than pulling out of 2000fpm. You can't escape physics. Likewise with the negative g part when you push down into the steeper dive. That's what makes pax vomit.

With respect, you're talking nonsense, both about vertical speed, and how you imagine PMDG designed the sim. Try hand flying some climbs and descents before pronouncing judgement on VNAV. I'm flying the same NGX as you and I don't see these problems. Maybe it's "pilot error" on your part?Kevin Hall

[NM5K 1]

I've brought these ridiculous climb/descent rates up before in other threads and PMDG just doesn't want to hear it. They go off of Boeing test flight videos with zero passengers and cargo which show 7000fpm climbs and apparently that's what they base their VNAV code off. But in the real world it's just not like that and I wish they'd consider all this feedback from real world pilots and controllers who work with this aircraft this every day. The VNAV behavior just isn't realistic.And those who say 6000fpm isn't felt any different than 1000fpm? Actually yes it is, because eventually you have to pull out of that 6000fpm dive! And it's going to be felt a lot harder or a lot longer than pulling out of 2000fpm. You can't escape physics. Likewise with the negative g part when you push down into the steeper dive. That's what makes pax vomit.

I've never seen anything which seemed out of line. No matter what the cost index.I've never seen a 6000 foot descent while in VNAV PTH. I've climbed at 4000 fpmearly in the climb, but that is quite normal considering the light load I'm running inthat particular plane.I've typically got about a 35% load in that one, and it climbs out quick. Quite normal..I never climb that fast when loaded down. There shouldn't be any severe divingin VNAV PTH as it's following the vertical path, and I've never seen the FMCcalculate a severe descent path. And really the cost index should have littlebearing on that, as the FMC should take the higher CI/speeds into considerationand plan accordingly. I never had any more trouble when running 80 than Ido 36.. You just move faster. Dunno what the deal is, but like Kevin, I'm notseeing it on this end.

[Paul_Smith 92]

I've brought these ridiculous climb/descent rates up before in other threads and PMDG just doesn't want to hear it. They go off of Boeing test flight videos with zero passengers and cargo which show 7000fpm climbs and apparently that's what they base their VNAV code off. But in the real world it's just not like that and I wish they'd consider all this feedback from real world pilots and controllers who work with this aircraft this every day. The VNAV behavior just isn't realistic.And those who say 6000fpm isn't felt any different than 1000fpm? Actually yes it is, because eventually you have to pull out of that 6000fpm dive! And it's going to be felt a lot harder or a lot longer than pulling out of 2000fpm. You can't escape physics. Likewise with the negative g part when you push down into the steeper dive. That's what makes pax vomit.

You are the pilot. You have big strong engines and very efficient wings. If you want to climb out at over 6,000fpm all you need to do is make sure you are reasonably light and do a full power take off. The only ridiculous thing is how you can think this is a problem with PMDG's VNAV?If you want your passengers to experience negative g then you need to aggressivly pitch down at over 3 degrees a second. (The reverse of the climb out roll which normally lasts between 3 and 4 seconds.) If you as pilot want to do that, fair enough, but you will have a hard job getting the FMC to do it for you. And again, that is not what makes passengers vomit, they are aware of rate of change and are made uncomfortable by changes to the rate of change. (Think fair ground rides)