• Rules of thumb - by Plane and Pilot

Groundspeed divided by 10 gives distance in NM travelled in 6 mins. Use half of this for 3 minute ticks.<br /> 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.

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.<br /> 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.<br /> To find out how fast to descend, multiply groundspeed by 5.<br /> 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,<br /> 5000 - 2000 = 3 =⇒ 3 x 3 = 9 NM<br /> 100 * 5 = 500 fpm<br /> So 6 miles from now, we need to start descending at 500 fpm to cross the VOR at 2000 ft.

Divide groundspeed by vertical speed (in hundreds)<br /> Example: 100 kts and descending at 500 fpm. 100 : 5 or 20 : 1

Multiply groundspeed by 5 (or add a zero and half it) to give rate of descent

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

I think this is the easiest method to remember - once you understand how a clockface is involved!<br /> It can be used for example, en-route for a hold to see how much offset to fly inbound to the beacon. (Outbound is flown 2 to 3 times this value)<br /> The key is to see the 4 quarters of the clock face and match the value to the wind.<br /> So, assuming the wind is going to be coming from anywhere between 0 and 90 degrees off the nose.<br /> If the wind is 15 degrees off the nose, use 1/4 of the crosswind component. (See the trick? 15 is at the 1/4 past on the clock face!)<br /> If the wind is 30 degrees off the nose, use 1/2 of the crosswind component. (30 is at the 1/2 past on the clock face!)<br /> If the wind is 45 degrees off the nose, use 3/4 of the crosswind component. (45 is at the 3/4 past on the clock face!)<br /> If the wind is 60 degrees or more off the nose, use the full crosswind component.<br />