seeing how you're in class A, how about when ATC asks you too.

For 3 degree descent, 5 x GS is a good approximation. The formula is derived from Tan (3°) = V/S ÷ GS.

Tan (3°) = .0524

.0524 = V/S ÷ GS ⇒ (.0524)GS = V/S

GS units are nm/hr, need to convert to fpm.

(.0524)GS nm/hr x hr/60min x 6000 ft/nm = (.0524)(100)GS = V/S

5.24 x GS = V/S(fpm) to be precise.

You mean when they ask you to "Descend at Pilots Discretion?" :rolleyes:

Stupid comment. Anyone listening to this comment and not using the brakes because of passenger comfort, large egos, or any other reason shouldn't be PICs. :rolleyes:

Methinks that was meant in satire/jest since it's on EVERY website/email of "pilot humor" or "things heard over ATC", etc.

But it's usually phrased as follows;

Controller: "what do you mean unable on the crossing restriction I just gave you, don't you have speed brakes on those planes"?

Pilot: "don't give us a restriction so late that it's impossible to make it. The speed brakes are for our screw ups, NOT yours".

Google it.

angle of descent
 

I was watching an aviation video where the pilot figured out his descent angle in order to make a fix and tell his autopilot what angle to use. Most people just use a descent rate in feet per minute. I never read of any easy way to do an angle calculation without a calculator, but this guy did it on his kneeboard real quick, and it was supposedly a real enactment, so I thought about it a little while, and came up with this fairly simple formula. Easy enough but still requires pen and paper.

>Divide the altitude to be lost by the distance in ft, and then divide by 1.7, and slide the decimal.

Ex. 5000 ft / 10 miles (61000 ft) = .082 / (1.7) = .0487° --> 4.8°

Anybody know one that does not require pen and paper?

It is a whole lot easier to use the 60:1 rule to calculate your flight path angle. Just get rid of the last 2 zeros in your altitude and you end up with 50/10= 5 degrees.

I never bother calculating my flight path angle. What is important to me is the descent rate required to meet the restriction. If i have to descend 5000ft in 10 miles at 200kts, my descent rate is 1667ft/min. That same crossing restriction at 400kts is 3333ft/min. Both of these are a 5 degree flight path angle, but there is a significant difference in the descent rate required.

Ah very good, that's what I was looking for (and had forgotten). Thanks!

That works. But sometimes when given a restriction with an altitude loss of say 15000 ft or more, it can throw much of it out the window. Especially with a ground speed change that could exeed 100 kts, etc.

Nope, nuthin' wrong with getting down before hitting the fix, but in places like Mexico where youre non- radar combined with terrain or fuel critical it can kind of mtter.

This is the technique that was being taught at UPT a few years ago:

Using the 10 degree pitch ladder on your ADI as 1.0 reference, select the pitch that represents the ratio of thousands of feet to loose over NM.

Example: you have to loose 15k' in 30NM, you would push halfway to 10 degrees, or 5 degrees.
Have to loose 5k' in 25nm, push to 2 degrees, etc.