Rules of thumb

Note: Memory aid - think of a round clock face. 15 min pass the hour is 1/4 (25%) of the circle. 30 min pass the hour is 1/2 (50%) of the circle. 45 min pass the hour us 3/4 (75%) of the circle.

Example:

Runway heading = 350°

Reported wind velocity = 320° / 10 kts

Angle between wind and runway = 30°

Crosswind component = 50% x 10 = 5 kts

Rate of descent to follow a 3° glideslope

5 x Ground speed

or (Ground speed x 10 ) / 2

Example:

Ground speed = 150 kts

Rate of descent required = 5 x 150 = 750 feet / min

Visual Descent Point (VDP)

Height Above Touchdown (HAT) or Minimum Descent Height (MDH), divided by 300 (for 3° glideslope)

or [Minimum Descent Altitude (MDA) - Touchdown Zone Elevation (TDZE)] / 300

Example:

Minimum descent height (MDH) = 600 ft AGL

Visual descent point (VDP) = 600 / 300 = 2nm from touchdown point

Visibility needed to see runway from VDP (non-precision approach)

Visibility (in meters) = 6 x minimum descent height (feet)

Example:

MDH = 500 ft

Visibility required = 6 x 500 = 3000 meters

Cater for gust factor during approach and landing

Add half of the gust factor to the final approach speed

Example:

Final approach speed (IAS) = 60 kts

Reported winds = 15 gusting to 25 (gust factor: 10 kts)

Speed to fly (IAS) = 60 + (10 / 2) = 65 kts

Hydroplaning speed

9 x square root of tire pressure (psi)

Example:

Tire pressure = 36 psi

Hydroplaning speed = 9 x √36 = 54 kts

Density altitude

Pressure altitude + [120 x (difference between actual air temperature and standard in celsius)]

Example:

Elevation = Sea level, Altimeter = 29.92, Temperature = 25°C

Density altitude = 0 + [120 x (25 - 10)] = 1200 ft

Estimate cloud base with temperature and dew point

[(Temperature - dew point) / 2 ] x 1000

Example:

Temperature = 10°C, Dew point = 5°C

Cloud base = (5 / 2) x 1000 = 2500 ft

ISA temperature (Standard temperature lapse rate)

Temperature decreases by approximately 2°C per 1000 ft increase in altitude

or (Altitude in thousands of feet x 2) - 15, then change the sign (positive to negative and vice versa)

Note: Standard temperature at sea level is 15°C

Example:

ISA temperature at 6000 ft AMSL = 15 - (2 x 6) = 3°C

ISA temperature at 12000 ft AMSL = (12 x 2) - 15 = 9 ; Change sign = -9°C

ISA pressure (Standard pressure lapse rate)

Pressure decreases by approximately 1"Hg per 1000 ft increase in altitude, up to 10,000 ft

Note: Standard pressure at sea level is 29.92″ Hg

True airspeed (TAS) at various altitudes

TAS = IAS + (2% of IAS x altitude in thousands of feet)

or TAS increases by approximately 2% for every 1000 ft increase in altitude

Example:

Altitude = 8000 ft AMSL

IAS = 200 kts

TAS = 200 + (4 x 8) = 232 kts

Bank angle for standard rate turn

15% of TAS

or TAS/10 + (half of the result)

Example:

True airspeed = 180 kts

Bank angle = 18 + 9 = 27°

Turn diameter or turn radius (for standard rate turn)

Diameter = (Ground speed / 100) + 0.1*

Radius = Diameter / 2

* Note: Below approximately 80 kts ground speed, the addition of 0.1 is not required)

Example:

Ground speed = 170 kts

Turn diameter = 1.8 nm

Turn radius = 0.9 nm

Convert between percentage and degrees (gradient and angle)

Percentage = (10 x degrees) / 6

Degrees = (6 x percentage) / 10

Example:

3° in terms of percentage = 30 / 6 = 5%

5% in terms of degrees = 30 / 10 = 3°

Horizon range

Square root of height (ft)

Example:

At 10,000ft, the horizon is at approximately √10,000 = 100 nm