Rules of Thumb

I think that the only two that I use are:

1. Cross wind calculations
10 degrees = 1/6 of winds speed = cross wind component
20 degrees = 2/6 of winds speed = cross wind component
30 degrees = 3/6 of winds speed = cross wind component
…
60 degrees = 6/6 of winds speed = cross wind component

2. For the aircraft that I fly, I need 5nm per 1,000ft desent required, at 500fpm.
So if I need to lose 5000ft to destination, then I need 5*5nm = 25nm to desend.

I can’t off hand think of any others that I use.

As you say, if you don’t use it regularly, you won’t use it.

The most useful one I’ve learnt is for crosswinds:

• Wind less than 30 degrees off the runway heading: crosswind component is negligible
• 30-60 degrees off: crosswind is about half the total wind
• More than 60 degrees off: crosswind component is the more or less the full wind speed

Also (somehow this was missed in my PPL training):

• A 3 degree approach is 300ft per nautical mile.
• The necessary vertical speed for a 3 degree glideslope in feet/minute is approximated by 5 * groundspeed in knots.
• More generally: required fpm is percentage gradient * groundspeed – e.g. for a 6% gradient at a ground speed of 90 knots you need about 540fpm
• From this, you can guess that height per nautical mile is 60 * % gradient – for that 6% gradient you need to climb 360 feet for every nautical mile.

Divide speed by 10 and you have distance in 6 minutes. Handy for a quick recliner for an estimate at a point when linked with….

500k chart, thumb tip is 10 miles

Descent planning distance start with required altitude change x 3… e.g take 3 miles for each 1000 ft

Standard decent.
Decent rate:
Multiply GS by 5 to get descent rate.
example: 150kt x 5 = 750 fpm.
Distance to start decent:
Multiply the altitude difference in thousands by 3.
Fl120 down to FL70 = 5kft x 3 = 15 miles. You should start the decent 15 miles out.

I use these rules on each and every flight.

The one-in-60 rule is the most useful one for me as it is applicable in many situations (e.g. wind correction, crosswind component…)

Also, start descent at 4* the altitude difference in 1000’s of feet.

From cruise to descent:
Reduction in RPM = rate of descent in FPM.
Works surprisingly well for a wide range of fixed prop aircraft.

Constant speed?
Reduction in inches MP = rate of descent in FPM / 100.

The most useful one I’ve learnt is for crosswinds:
•Wind less than 30 degrees off the runway heading: crosswind component is negligible
•30-60 degrees off: crosswind is about half the total wind
•More than 60 degrees off: crosswind component is the more or less the full wind speed

You better unlearn that quickly. At 30 degrees it is EXACTLY half, and at 60 degrees it is 86%.

Dublinpilot’s is much better – easiest remembered as “clock code”.

• 15 degrees —> 15 minutes are a quarter hour —> 1/4 of wind is crosswind component
• 45 degrees —> 45 minutes are three quarters of an hour —> 3/4 of wind is crosswind component
  An you never use more than 60 degrees / “one hour”

Two equally useful methods for wind corrections in the air:

• max drift is (windspeed / miles per minute). You do know how many miles per minute you fly, right?
• drift (or wind correction angle) is max drift * clock code (as per above)

The other one (which I prefer, as I like multiplication more than using the division implied in the “clock code”

• drift for each 10 degrees of crosswind is (wind speed / a tenth of true airspeed), but only take into account up to 60 degrees.
  This is mathematically exactly the same as the above.

Accuracy of all these is better than +-10% for most data points, only at 60 degrees it is around 15%, in any case more accurate than the wind forecast…

Density Altitude: every 8.3 degs C above ISA = 1000 ft increase. ISA of course is 15C minus field elevation in thousands of feet multiplied by two (2C being standard lapse rate).

Example: FE = 7000ft. OAT = 10C. ISA should be 1C. Difference = 9C. DA therefore approx 8100 ft.

This errs a bit on the high side, which is rather a good thing in practice.

Just came across this site which seems to cover a large number of these.