Hi guys great aircraft firstly I'm loving it, I only have one query when i do descents, I always seem to be struggling to get to the required altitudes as stated in FMC. I always program my flights properly with weather aswell. I might be doing something wrong it just seems to happen all the time, then I get messages in FMC like des path unachievable or similar. Any help or guidance will be greatly

appreciated regards Wayne HART.

 

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Hello,

 

Descend with the NGX needs some planning before commencing and some factors has to be taken into consideration before starting the descend, I am no expert, however, I read some topics regarding this, main point or some of it are as follows:

1. Wind direction, tail wind will mean that you will need more distance than, the estimated distance by the FMC.
2. The model of plane, as per my personal experience the 600 behaves different from 700 and so on for 800 & 900 series, so you will have to try and see each descent tendencies with similar configurations. 
3. The weight of the aircraft, is important factor as well the heavier the plane the more efforts needed to control the speed.
4. Don't by shy   to use the speed breaks bellow I think FL210 to slow down the aircraft if needed.
5. @ the FMC, if I get an economical descend speed of 289/.77M for example I reduce it to 280/.72 to give myself an extra distance.
6. I usually when I feel I need extra distance to complete my descend I start descending about 10NM before the TOD point this also it helps for more gradual  descend  starting 1,000ft/m and so on.
7. The message you get on your FMC is very realistic and should be considered as a first warning that you have to take certain measures to achieve the planed descend path.

I hope that was helpful 

 

Best regards and happy flying

 

 

I might be doing something wrong it just seems to happen all the time, then I get messages in FMC like des path unachievable or similar.

 

Alaa provided a great explanation of the several factors.

 

Many of the DES PATH UNACHIEVABLE messages I've gotten have simply been issues of the FMC not having the whole picture.  As an example, the LENDY STAR into JFK ends at the LGA VOR with an altitude restriction of FL190 14nm to the west of it.  That means you're at FL190 with only 23 (direct) nm between you and JFK.  It's assumed you'd need about 60nm to descend from FL200 to sea level.

 

All the FMC likely sees is that altitude restriction (LENDY at FL190), and the approach (let's say the ILS 22L) only 23nm away down at 3000.  The FMC assumes you're going direct between those two points when trying to calculate its descent.

 

*DING* I CAN'T DO WHAT YOU'RE ASKING ME TO

 

In the real world, you'd be vectored and fly the descent in FL CH or V/S, which means it doesn't matter what vertical path the FMC calculates, or can't calculate.  It doesn't know what the vectors will be, and how many extra miles you will be flying to kill altitude, so it's simply saying "given what I know right now, I can't do that."

 

As you're probably not a controller, there's no way you'd know that either.  Some places, like Orlando (KMCO) have STARs with lost communications procedures that you can use to assume how they'd vector you, though many places don't.

 

Don't assume the STAR dumps onto the approaches in busier locations like DC and NY.  They are heavily dependent on vectoring for sequencing, so the distance between the end of the STAR and your turn inbound for the approach varies.  The DC-area arrivals are a little better aligned, altitude-wise, but NY's airspace is so complicated, they don't have that luxury.

 

...and now you know more than you'd ever need to know.

Thankyou gents appreciate it.

Great explanation of the Lendy arrival Kyle.   I was always curious about what vectors ATC gives to traffic on that STAR, between the Lendy waypoint and the FAF for the applicable ILS runway.  If anyone is curious, you have two sources that can show what the real life controllers assign for vectors:

 

1. Flightaware or Passur.com - Just pull up KJFK in the Flightaware "Airport Tracker/Info" box at the bottom left of the main page, select "View Activity", and you will be presented with a live map of the arrival activity.  You can then get an idea of which vectors to use, as well as altitude and ground speed indications of the arriving traffic, and can use that information in your own simming sessions.  

Passur.com also has a live map of selected U.S. airports, KJFK among them, and gives an even nicer graphical representation of traffic movements that you can use to simulate your own arrivals to KJFK.

Unlike Flightaware, with Passur you can lookup historical data, so if you are simulating a real flight in the sim like I do, it's very easy to get accurate vectors and other flight data used IRL.

 

2. If you want specific speeds and altitude instructions that the boys/girls in real cockpits are receiving from the controllers, just go to LiveATC.net and find a live or archived feed, and you get the answers to your questions straight from the horse's mouth!

 

I use both of the above sources for basically all my flights, call it OCD, but I only fly real routes using the same equipment (NGX) as the real flights and I enjoy researching real world conditions and procedures and applying it to my simulator sessions.   If only I could get the loadsheet of the real flights so that I could match their weights!

Hi guys great aircraft firstly I'm loving it, I only have one query when i do descents, I always seem to be struggling to get to the required altitudes as stated in FMC. I always program my flights properly with weather aswell. I might be doing something wrong it just seems to happen all the time, then I get messages in FMC like des path unachievable or similar. Any help or guidance will be greatly

appreciated regards Wayne HART.

 

Sent from my iPad using Tapatalk HD

And make sure your engines are at idle. I've never gotten a "Descent Path Unachievable" RW.

 

 

Great explanation of the Lendy arrival Kyle.   I was always curious about what vectors ATC gives to traffic on that STAR, between the Lendy waypoint and the FAF for the applicable ILS runway.  If anyone is curious, you have two sources that can show what the real life controllers assign for vectors

 

Thanks!  Luckily, I've been able to spend a lot of time around the N90 and PCT controllers to pick up on what they do, and why it's done.

 

Here's a third source that's equally as good, to get a better visualization of it all: http://nyartcc.org/N90Flows/NY_AirSpace.swf

 

One of the guys I work with made that (though, some may note, it's on a VATSIM-affiliated server).  I can't remember the original FAA address for it...some link off the command center site, though.