Rules of Thumb
Contents
En Route
Time ticks
Groundspeed divided by 10 gives distance in NM travelled in 6 mins. Use half of this for 3 minute ticks.
e.g. with a groundspeed of 110 kts, the distance flown in 6 minutes will be 11 NM. It will take 3 minutes to fly 5.5 NM.
Descent
Top of Descent calculation
This calculation can be used either to know when to start your descent to an IAF or ATC have given an instruction to cross at or below a certain altitude by a certain point.
To find when to start down, multiply the height between where you are now and where you have to be (in 1000's of ft) by 3.
To find out how fast to descend, multiply groundspeed by 5.
Example. We are at 5000 ft and need to be at 2000 ft crossing a VOR. We are doing 100 kts and the DME says we are currently 15 NM from the VOR,
5000 - 2000 = 3 ==> 3 x 3 = 9 NM
100 * 5 = 500 fpm
So 6 miles from now, we need to start descending at 500 fpm to cross the VOR at 2000 ft.
Approach
Glide ratio calculation
Divide groundspeed by vertical speed (in hundreds)
Example: 100 kts and descending at 500 fpm. 100 : 5 or 20 : 1
Rate of descent down a 3° glideslope
Multiply groundspeed by 5 (or add a zero and half it) to give rate of descent
Height above ground vs distance to runway
As a glide slope check (or if G/S is not available), multiply nautical miles to go by 300 to give current height above the ground
