backpacker
If a Cessna doing a GS of 90 kts wants to lose 5000 feet to be over the airfield at a certain height. And using 1500 fpm average which we do in the faster stuff.
The 3times rule would say approx. 15 miles.
That would take you 10 minutes.
At 1500 fpm you would be at your planned altitude after 3.33minutes. Well before the planned time.
In this case you would need only 500fpm to be there at your planned height and time.
Therefore the three time rule will not work for an aircraft at 90 knots. But try the same at 270 knots and it works fine.
What i am trying to get across is that, if you use a fixed formula (3times), you need a constand ROD and speed ('ish) or it wont work. The 3 times is really for faster aircraft as the above example dictates.
Fright levels one seems to be quite good though.