# VOR and VFR

Taylor First Officer

hello everyone. ok, i would like to know how you know when to descend inflight if you are flying by vor or vfr. for me it is always hard to tell when to descend. also, i noticed on some airliners there is no gps, how do you know where you are. any help appreciated. thanks. 😀 😀

## 8 Responses

CRJCapt Chief Captain

Taylor wrote:

hello everyone. ok, i would like to know how you know when to descend inflight if you are flying by vor or vfr. for me it is always hard to tell when to descend. also, i noticed on some airliners there is no gps, how do you know where you are. any help appreciated. thanks. 😀 😀

As a general rule of thumb, you want to descend on about a 3 degree slope. Take your altitude above ground level[AGL](drop the last two digits), divide by 3. The descent rate needed is 1/2 of your ground speed(use Airspeed if unsure about ground speed). 9,000- 90/3=30 Start descent 30 nm. Ground speed 150 kts-use descent rate of 750 FPM or 800 to make it easier.

Airliners normally navigate with the Flight Management computer(FMC) that has a GPS sensor. Some don't have a GPS sensor but utilize VOR DME information for position computation. Airliners can also utilize VOR and ADF navigation.

Taylor First Officer

thank you so much it really helped 😀 😀

Taylor First Officer

ok sorry but can you explain this a little more i dont see where this comes in. thanks=

The descent rate needed is 1/2 of your ground speed(use Airspeed if unsure about ground speed).

😀 😀

CRJCapt Chief Captain

The distance to descend and the rate of descent are connected.
If you descend at 2000 FPM or 50 FPM, the 30 miles means nothing. Your ground speed(GS) also plays a part because if your GS is 400 kts then your rate of descent will be greater than if your GS was 90 kts. There is a table of what descent rates equal what angles of descent at specific GS's. The easy way is to just use the rule of thumb of 1/2 your ground speed. It's an approximation but works. I said use airspeed(AS) if you don't know your GS because you may not know your GS. AS is close enough unless you have a very strong wind that causes your AS and GS to be significantly different. You don't have to be exact. You don't have to descend on a 3 degree angle, it's just considered normal and it makes it easier on the aircraft and the math. In the real world you can't be exact anyway. Winds change at different altitudes so GS varies and you can't maintain exactly 754 FPM.

Descent Rate Table
http://www.flightsimbooks.com/flightsimhandbook/366-1.jpg

Taylor First Officer

o ok thanks a lot. 😀 😀

Taylor First Officer

this is really helpful but can i give you an example to make sure i got it-

ok we are at 35,000 feet going 300kts. i need to start my 3 degree descent at around 117 nm out. and i need to descend at a rate of 1500 FPM. i think this is right and if i am forgetting anything let me know please. thanks 😀 😀

CRJCapt Chief Captain

Taylor wrote:

this is really helpful but can i give you an example to make sure i got it-

ok we are at 35,000 feet going 300kts. i need to start my 3 degree descent at around 117 nm out. and i need to descend at a rate of 1500 FPM. i think this is right and if i am forgetting anything let me know please. thanks 😀 😀

Pretty close, starting your descent at 117 instead of 105 miles won't hurt anything.

Using the basic rule of thumb:
3 X 35 =105 nm. Descent rate is correct, 1500 FPM.

Taylor First Officer

ok thanks for all your help. 😀 😀

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