Rule of thumb

-noun

1: a method of procedure based on experience and common sense

2: a general principle regarded as roughly correct but not intended to be scientifically accurate

In aviation we use a lot of these. They help us to reduce workload in the cockpit while flying, since we can do certain calculations in our head (or on paper) in an easy way instead of fumbling with charts, manuals and calculators.

Here is a list of some rules of thumb, that I've gotten to know so far (there are literally thousands of them out there..).

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Level Off procedure

∆ feet = Vertical Speed (feet/min) / 10

Climbing to 3000 ft. with Climb Rate of 500 fpm

Level off at 500 / 10 = 50 feet before -> level off at 2950 ft for 3000 ft

Vertical Speed to get back to desired altitude

V/S (feet/min) = 2 x Altitude OFF

If on 3250 feet instead of 3000 feet, correct with V/S = 2 x 250 ft -> 500 feet/min

Off-Track distance

Off-Track Distance = ∆° x distance to station / 60

10° off track  x  12 NM from station Off-Track Distance = 10x12/60 = 120/60 = 2NM

Slant distance overhead a DME - station

each 6000 feet altitude -> 1 NM DME

Flying over the station at 4000 ft it is 4000 / 6000 = 0.67 NM on DME

Re-intercept Radial

Re-intercept Angle = 3 x Off-Track angle

On R-180 outbound instead of R-185: correct 15° to rejoin

Express Glide slope Angle in %

% = degrees x 10 / 6

3° Standard ILS Glide slope: 3x10 / 60 = 30 / 60 = 5 %

Rate of Descent required to stay on a specific Glide slope (in %)

Rate of Descent (fpm) = Ground Speed x %

TAS 90 kts, 20 kts tailwind, Glide 3° = 5% -> Rate of Descent = 110 x 5 = 550 fpm

Rate of Descent required to stay on 3° Glide slope

Rate of Descent (fpm) = Ground Speed x 5

TAS 90 kts, 20 kts tailwind -> Rate of Descent = 110 x 5 = 550 fpm

Roll-out from a turn

Roll out lead = Bank Angle / 3

Bank 15° Right turn to Heading 090 start roll-out 5° early on Heading 085

Bank required for a Standard rate turn (2 minutes for 360°)

Bank Angle = 15% TAS

TAS 90 kts -> Bank Angle required = 9 + 4.5 = 13.5°

Calculating Density Altitude

1°C equals 120 feet

-if temperature is higher than standard (15°C) multiply difference from 15°C with 120 and add to Pressure altitude.

-if temperature is lower than standard (15°C) multiply difference from 15°C with 120 and subtract from Pressure altitude.

Example: 25°C -> 25-15=10 -> 10 x 120 = 1200 feet difference

Find Pressure Altitude

Set altimeter to 29.92 and read PA from the altimeter

Standard Lapse Rate = -1" hg. for each 1000' increase in altitude

Standard Lapse Rate = -2°C / -3.5°F for each 1000’ increase in altitude

During each 1000' of climb, expect to see a loss of approx. 1” of manifold pressure

During each 1000' of climb, expect TAS to increase 2%

The width of one finger = ~5NM on a sectional chart (average person)

Tip of the thumb to the knuckle = ~10NM on a sectional chart (average person)

Calculate Reciprocal Heading

+/- 200 -/+ 20

Examples: 360 -200 +20 = 180 ; 040 +200 -20 = 220

For VASI approach slope lights:

"Red over white you're all right, red over red you're dead."

While flying:

"Red on right, fearful sight."

Note:

To see more ground, push forward

To see more sky, pull back