TOD Calculations??

[cloudpuncher]

I can vaguely remember from training that there is a some quick way of working this out, but I can't seem to recall it.

Something to do with height in feet x4 +10 to slow down, gives distance in NMs to commence descent. Renewing my IR soon so this would be helful, any info greatly appreciated!

Cheers

CP:ok:

[wobblyprop]

erm, nearly i think its 3 x height + 10 to slow down.

e.g. FL330 = > 33,000ft

=> 33 x 3 = call it 100 + 10 = 110 nm.

I assume that if you have intermediate levels you could times the difference by 3 and still get a sensible figure.

[ecj]

For your unpressurised ac, which I assume you will renew your IR in, the x4 rule + d is fine, with a say 700 fpm ROD, with a max of 1000 fpm.

The x3 rule is really for pressurised ac.

[FLEXJET]

For an unpressurized aircraft, I have been told:

Loss of altitude divided by 2 (as for 2° descent path)

Exemple: you want to leave FL070 down to 2500' (forget about pressure altitude/altitude difference here).

70 - 25 = 45 and 45 / 2 = 22.5 = 23 NM

That will give you, for a 150 kt Ground Speed, a 500 fpm rate of descent. [(150/60) x 2]

As 700 fpm is the maximum recommended for passenger confort and health, a 210 kt Ground Speed descent should be the maximum usable for an unpressurized aircraft.


FLEXJET

[no_HANDLE]

Number rule;

120kt (ground speed) = 4nm @ 500ft/min
150kt = 5nm
180kt = 6nm

and so on...........

The way it works (unpressurised A/C) take you alt ie 9000ft then multiply it by that GS figure above and you will get your TOD.

example: your at 9000ft doing 180kt GS what is your TOD?

9000 = 9
180 = 6

9x6=54 (TOD is at 54nm)

Nice and easy, good luck for your renewal
:ok:

[Onan the Clumsy]

I just subtract 1500' from the cruise altitude - which fortunately is always VFR - and multiply by six

The reason is that all the airports I use are at about 500' and I'm doing about 180 kts and I'm looking for a 500fpm descent (not that I can ever hold that mind)