can anyone chime in on calculating feet per minute. 3 degree is gs / 2 + 00
what would it be for2 to 1?
There is another form of the rule of thumb you quoted and it can be used for any descent angle. It is:
speed in miles per minute x descent angle x 100
eg: for 3º approach @ 120 gnd spd you would have:
3 x 2 (nautical miles per minute) x 100 = 600fpm
...as can be seen it is the same rule at the end of the day.
The rule of thumb for descent angle is number of FLs (ie increments of 100ft) ÷ miles.
eg for a '2:1' descent you would have:
10FLs ÷ 2 miles = 5º angle
Putting it all together for a '2:1' @ 180 gnd spd:
10FLs ÷ 2 = 5º
5 x 3 = 15. Rate of descent = 1500fpm.
Rules of Thumb: Descent VVI