The Cost Index is used for calculating climb and cruise target speeds.It has hardly no effect in a VNAV descent.It is important to use the VNAV pages, Climb-Cruise and Descent during each of those phases of flight.Also, Drag Required is not a warning or an error. The speed brakes are a pilots best friend in a VNAV PATH descent.

It has the same effect going down as it does going up. The higher the CI, the closer to the barber pole you'll be. For whatever reason, my company overrides the Econ descent and uses a fixed .78/280. I think the lower descent speeds can annoy the controllers.

It has the same effect going down as it does going up. The higher the CI, the closer to the barber pole you'll be. For whatever reason, my company overrides the Econ descent and uses a fixed .78/280. I think the lower descent speeds can annoy the controllers.

I utilize this technique myself. It allows for steeper descents most of the time, especially with a head wind, therefore it saves fuel. The FMC usually has me descending at over 300KIAS, so my descent can start as far as 170NM from the field. I'd rather be at FLXXX for as long as possible to maximize fuel saving (My VA uses an FS Economy style approach, so I try my best to help save vDollars). The descent rate is greater of course, but not to the point pax would complain (I use FS Flight Keeper as my ACARS, so it tells me if I've been *bad*). If the STAR doesn't mandate an altitude, I'll usually be above it!

I utilize this technique myself. It allows for steeper descents most of the time, especially with a head wind, therefore it saves fuel. The FMC usually has me descending at over 300KIAS, so my descent can start as far as 170NM from the field. I'd rather be at FLXXX for as long as possible to maximize fuel saving (My VA uses an FS Economy style approach, so I try my best to help save vDollars). The descent rate is greater of course, but not to the point pax would complain (I use FS Flight Keeper as my ACARS, so it tells me if I've been *bad*). If the STAR doesn't mandate an altitude, I'll usually be above it!

The higher the descent speed, the longer you can stay up at altitude. High speeds work great until you have to slow for traffic or turbulence.

That's pretty much what I'm saying, we just have a different terminology for it, I think. I was taught descent rate is Rate of Descent. So to me, descent speed is the indicated speed in knots or Mach.

That's pretty much what I'm saying, we just have a different terminology for it, I think. I was taught descent rate is Rate of Descent. So to me, descent speed is the indicated speed in knots or Mach.

We'll just have to agree to agree. :)

Sorry, I posted my last reply from my phone. Having just reread it, it doesn't come across intended. My apologies for any confusion.What I meant earlier, was that I stay at altitude as long as possible, with two main factors governing my ToD point:- A point that allows a steep, yet comfortable, Rate of Descent as late into the flight as possible, or;- A descent based on requirements by ATC or charts. Being (mainly) a rotorhead in real life, I have limited exposure to real-world operations in airliners, so please feel free to teach me the correct way to determine your ToD if I'm way off!

I think people need to realise that the CI is aircraft specific, not a one size fits all figure. Virgin Australia (old Virgin Blue) for instance use 9 or 10 as the CI for the 700 and 800 series. Qantas use a CI of between 200 and 300 for the B744 and I am sure that the MD11 operators use something else. Apart from all that there is always the good old rule of thumb, cruise level divided by 3. e.g. FL330 / 3 equals 110 nautical miles as the TOD. You can add or subtract from this for expected head or tail wind. It is also a good 'how goes it' check during the descent.Neil Bradley

I would be nice to have some input from the developpement team on this though, maybe it could bring a better understanding as to how the TOD is calculated so people who like me that use a high CI don't nose dive on every descent.

I'm probably not the first one to report this, but for some reason my TOD is always off, resulting in the plane going into 6000fpm descent or even more often VNAV kicking off with the Descent path unachievable error on the FMC.No matter what I try it constantly does this, I always set the runway and the correct altitudes for the STAR yet it constantly happens, am I missing something here? I even try starting the descent early but no luck. Is this a bug or is it something I'm forgetting here?ThanksTrystan

Tristan, occasionally I have the same problem. I think it has to do with altitudes restricitons and waypoints. I feel in those instances the FMC is not calculating the TOD correctly.Example: some STARs have waypoints with altitudes restrictions either ´at or above´. Or ´at or below´. It is my experience that the FMC will sometimes bypass a restriction because it can make the next. If a first restriciton is AT FL100 but the next is FL80A is will not make FL100 in time. Hence it will not be at a certain AT level, if there is a At or Above following that. I haven´t really pinpointed it, but that´s where it starts. To prevent problems during descent, I change these ´at or aboves´ or ´at or belows´ to just AT. That simplifies it and smoothens the descent. But then occassionaly when reaching TOD, (the point the FMC has calculated), I am already far above the glideslope and it is hard to catch up again. Thanks to a video postend here earlier I now know how to do that.So it is my experience it has to do with altitude restrictions. If there are multiple in the STAR, the FMC has difficulty in calculating the right descent path and will sometimes show behaviour you see.Menno

You can try idle descent, its for E170 but works well with the 600: Dist = 2 x FL(difference)/10 + 15

I would be nice to have some input from the developpement team on this though, maybe it could bring a better understanding as to how the TOD is calculated so people who like me that use a high CI don't nose dive on every descent.

The Top Of Descent T/D) is calculated backwards from the End Of Descent (E/D) point and takes into account the approach and flap speeds,the waypoint constraints and the 250/10,000 restriction. Wind and temperatures are also taken into account and the result is the T/D point.If you are having problems with speed during descent, you need to look carefully at the waypoints and how close or far apart they are.Are their restrictions achievable ? If not then you need to adjust them. VNAV is a great tool but it can't perform miracles.Fred.

I've raised this issue numerous times. the NGX can't handle the descent calculations. so many times on standard descent profiles to intercept a STAR, i get about halfway down when I get the 'descent path unachieveable' message and it just leaves me hanging there. Thats the only let down I have with the NGX (both 700 and 800 models). Either that or I have to descend with spoilers up almost the whole way. I've ridden 737's a hundred times (as most of us have) and I very rarely see pilots use the spoilers so I don't know why I'm constantly having to do so ingame.Plus I understand the 737 is a slipper bird and takes a while to slow down but thats half the problem...the VNAV calculates the descent profile to reach approx 10 miles (say) away from the airport at around 4000 ft but at 240 and then expects to slow down (usually marked with 'decel' or something in the fmc) which doesn't work. I then end up landing at 170 kts!!Surely the PMDG devs can have a look at this. I don't get this issue with the 747x or leveld 767.

Hi everybody, after to read your last post I'm not feeling alone about this problem.Really this issue, I think is pointing a building error of the game.I have tried to make many times a correct desdent, it has been imposible, I have had to make all descents with airbrake spoilers up or otherwise to arrive to runway to 240knts.I feel quite a lot disapointed, altough actually, the cockpit is very very nice as well as the FMC. I like this plane but we also need a solution.Thanks

I've raised this issue numerous times. the NGX can't handle the descent calculations. so many times on standard descent profiles to intercept a STAR, i get about halfway down when I get the 'descent path unachieveable' message and it just leaves me hanging there. Thats the only let down I have with the NGX (both 700 and 800 models). Either that or I have to descend with spoilers up almost the whole way. I've ridden 737's a hundred times (as most of us have) and I very rarely see pilots use the spoilers so I don't know why I'm constantly having to do so ingame.Plus I understand the 737 is a slipper bird and takes a while to slow down but thats half the problem...the VNAV calculates the descent profile to reach approx 10 miles (say) away from the airport at around 4000 ft but at 240 and then expects to slow down (usually marked with 'decel' or something in the fmc) which doesn't work. I then end up landing at 170 kts!!Surely the PMDG devs can have a look at this. I don't get this issue with the 747x or leveld 767.

Hi everybody, after to read your last post I'm not feeling alone about this problem.Really this issue, I think is pointing a building error of the game.I have tried to make many times a correct desdent, it has been imposible, I have had to make all descents with airbrake spoilers up or otherwise to arrive to runway to 240knts.I feel quite a lot disapointed, altough actually, the cockpit is very very nice as well as the FMC. I like this plane but we also need a solution.Thanks

Strange....I have done allot of flights on Vatsim, & I mostly use Vnav dec. For me the TOD & Vnav Path descent works like a charm! & the CI don't matter I have used from 20 to 500.

Hi everybody, after to read your last post I'm not feeling alone about this problem.Really this issue, I think is pointing a building error of the game.I have tried to make many times a correct desdent, it has been imposible, I have had to make all descents with airbrake spoilers up or otherwise to arrive to runway to 240knts.I feel quite a lot disapointed, altough actually, the cockpit is very very nice as well as the FMC. I like this plane but we also need a solution.Thanks

After you select the approach, what does the FMC want for a speed at the IAF or FAF? Is it really 240? Or is it something closer to 160?