flying with no fmc

[steven jacobs 1377500]

hey guys im somewhat new here (ive flown on the vat network in the past but that was almost 10 years ago) and wanted to know how exactly to fly with no fmc. when atc is offline what is the easiest way to know when to start your decent and how do you go about vectoring. ive been playing aound with the final version of vasfmc but keep having difficulties along with the fact thagt i dont always flly a boeing or airbus. any help is greatly appreciated

[Trent Hopkinson]

when atc is offline what is the easiest way to know when to start your decent

 

3 times table.

 

What is your Flight Level?

 

"FL330"

 

how high is the airport?

 

"It's 1000ft above sea level according to the chart/airport info"

 

33 minus 1 = 32

 

32 times 3 = 96

 

Descent has to start at least 96 miles out.... but I'm doing 300 knots and I don't want to cross the runway threshold at 300 knots... It takes 10 miles to lose 100 knots and my landing speed is 135kts or so... Round to the nearest 100.

 

96+20= 116

 

Top of descent is 116 miles.

 

How fast should I descend?

Groundspeed = 462

462 times 5 = 2310

.... descend at 2400ft/min.

 

Keep adjusting descent rate very 50 or so knots. Tend toward the "higher end" of rounding up

 

400 knots groundspeed? 2000ft/min descent

 

250 knots groundspeed? 1300ft/min

 

140 knots groundspeed? 700ft/min

 

Remember to take into consideration any corners. So if you are flying a straight in approach to the airport, this is easy, but if you're doing a series of big turns, say entering a downwind leg, maybe remove the downwind leg distance from your calculation so you don't end up on a long level segment.

 

TL;DR:

Descent initiation point distance in nautical miles = 3 times your height in feet plus 10 miles per 100 knots deceleration.

Descent rate = groundspeed times 5 (recalculated for every 50 knots in speed reduction)

 

This will achieve a slightly power-on 3 degree descent path so you should have a little wiggle room for tailwind

[Jim Hurst 1353723]

I "ballpark guess" it along the same lines as Trent (but not as rigorously).

 

Basically, when you're up in the Flight Levels with civilian stuff, I figure you're going (more or less) 5 miles / minute.

 

Then, using 2000 fpm I figure out how many minutes I need to get to the altitude I need. So, say I'm @ FL380 and I have to meet a 12000 ft crossing restriction at a fix. So, 38-12 = 26. I need to lose 26000 feet of altitude, and at 2000 fpm, that's ~13 minutes.

 

So, ~13 minutes of flight at ~5 miles / minute is ~65 miles, downrange from the fix I need to cross.

 

At (or a little before that), I pull the power back a bit (to maintain ~250-275 IAS), descend at 2500 fpm (a little steeper than above), and I'm usually right where I need to be right about when I need to be there. Of course, It's never a bad idea, to monitor that descent as it proceeds, and tweak it (if needed), as you get a bit closer to your level off point.

 

Obviously, that's quite a bit less rigorous than Trent's excellent post, but it's basically the same idea, with (for me) some easier math, and it has worked pretty well... At least, "Good Enough for Government work", and in my book, the FAA & ATC definitely counts as "government".

 

Hope that helps!

 

Regards,

Jim

Edited June 30, 2017 at 06:31 PM by Guest

[Don Desfosse]

Similarly, I just ballpark at 4nm per thousand feet I need to descend to determine how many nm out I should start the descent ([Mod - Happy Thoughts]uming a civilian tubeliner descending at an average of 1800fpm).

[Randy Tyndall 1087023]

All excellent ideas. For me, if I want to get to the right altitude with as little fuss as possible I simply open the default GPS if the aircraft has one, most freeware do and all default do as far as I know, and plug in a "direct to" the airfield or intersection (or one near it if it's not in the default navdata). The GPS will tell me how many minutes to the field/waypoint/fix. So if I am at 35,000 feet and I need to be at 9,000 feet by waypoint X I plug in the direct to waypoint X. The GPS says I am 14 minutes from reaching it. I now know if I descend at 2,000 fpm I will be at 7,000 in 14 minutes...roughly...and plan accordingly. The descent will most likely increase your speed so there will be some fine tuning to do with your descent rate as you get closer, but it has always worked for me and I have never gotten a "ding dong" from a controller for busting a speed or altitude restriction/crossing.

 

Randy