Quick way to calculate ROD

[bill fly]

Pocket descent tool

A senior captain showed me this simple method when I was a new copilot and high on descent.
It works on any aircraft with a Mach meter.

Just 2 calculations:

1. FL / Dist to go in NM = Degrees

2. Degrees x Mach Number = ROD in fpm

You can either use this in real time to assess quickly if you can make a required FL / Alt at a given point (whether you need extra drag is a judgement you then make)

Or you can use it in advance to calculate a descent point with your type standard descent angle.

It was handy on the older types where, because of cabin pressure restrictions the initial descent to FL 300 was at low rate of 750 rpm so with Mach .75, a one degree descent = 10 miles per 1000 ft,
followed by initially closer to a 4 degree descent, at Mach .7 = 2800 fpm.

Then, as the Mach number reduces in the descent, so you reduce the ROD.
Whether you need extra drag is a judgement you then make.

A handy tool and it always works, though it requires thinking outside the ‘magenta’ box.
You can use it to calculate a climb too, within performance restrictions.

Edit - see also Bullethead just above…