Aviation Av iation Rule Ruless of Thumb Thumb
Listed below are some tried and tested aviation rules of thumb that can help you become a safer, more competent pilot. This This is just a sampling of the many that exist. If you have any that you’d like to add, please leave a comment. Unless otherwise specified they are intended for light aircraft. Never, at any time should they be sub s ubstitut stituted ed for figure f iguress foun fo undd in your specific aircraft Pilot’s Operating Handbook (POH) or Airplane Flight Manual (AFM). Nor should they be used as a substitute for any Federal Aviation Regulation (FAR), or just plain old common sense. How’s that for fine prin p rint? t?
AIRSPEED/ALTITUDE/TEMPERATURE •
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Standard Temperature (ISA): 15°C (59°F) at sea level. ISA
decreases 2°C (3.5°F) per 1,000 foot increase in altitude True Airpseed (TAS): Add 2% to indicated airspeed (IAS) for every 1,000 foot increase in altitude Density Altitude: For every variation of ±15°F or ±8°C from standard temperature at a given pressure altitude, density altitude increases/decreases 1,000 feet Air Density/Humidity: For every 20°F temperature increase air density decreases 2-3% (moisture holding capacity doubles) Relative Humidity: Dew point/Temperature = Percentage [Example: (9°C/19°C) = 47%] Density Altitude: Increases or decreases 120 feet for each 1 degree Celsius that the temperature varies from standard temperature Density Altitude: Outside temperature minus standard temperature multiplied by 120 plus pressure altitude [Example: (OAT-ISA) x 120 + PA = DA] Calculating standard temperature at altitude: [Example of 12,000 feet: (12 x 2) -15=9. Convert to a negative. -9°C at 12,000 feet] Celsius to Fahrenheit (15°C, for example): (15 x 2) + 30 = 60°F (59°F) Fahrenheit to Celsius (59°F, for example): (59 – 30) ÷ 2 = 14.5°C (15°C) Maneuvering Speed (Va): Reduce Va by one-half the percentage of weight reduction. [Example: Va at 3,000 lbs = 100kts.; 2,400 lbs = 20% reduction on weight. Reduce Va by 10 kts.] Maneuering Speed Formula: Va2 = Va√(W2 ÷ W1); whereas Va2 is calculated maneuvering speed, Va is maneuvering speed at gross weight, W2 is reduced weight, and W1 is gross weight Manuevering Speed (Va): Subtract 1 knot for each 100 pounds under gross landing weight
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Stall speed: As weight doubles, stall speed increases by √2, or 1.414
A IRCRAF T LOADING •
Weight of 100LL: 6.0 lbs/gal
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Weight of Jet A: 6.75 lbs/gal
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Weight of 50W Oil: 7.5 lbs/gal (1.875 lbs/qt)
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Jet A lbs. to gallons: Divide pounds required by 10, add 50%
[Example: (2,000 lbs. ÷ 10) x 1.5 = 300 gallons) OR drop the zero then add 50%] •
Weight x Arm = Moment
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Total Moment ÷ Total Weight = CG (inches)
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CG Distance Aft of LEMAC ÷ MAC = CG in % MAC
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Weight Shift Formula: (Weight shifted/Total weight) = (Distance CG
shifted/Distance weight shifted)
TAKEOFF/LANDING PERFORMANCE •
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General: Add at least a 20% safety margin to all POH/AFM
performance figures, as insurance Takeoff distance: Increase by 10% for each 1,000 foot density altitude above sea level Ground roll: Increases or decreases by 10% for every 10°C change in temperature from ISA Ground roll: For every 10% change in weight, ground roll changes 20% Abort distance: Abort the takeoff if the aircraft has not achieved 70% of its flying speed by the time it has used 50% of the runway Rotate speed (Vr): Generally equal to 1.15 Vs Obstacle clearance: The distance/time to clear an obstacle is reduced by 5% for every 100 lbs. below max gross weight Runway gradient: A 1% airport grade will affect the aircraft by 10% over what is stated in the POH/AFM Tailwind: A tailwind of 10% of your approach speed will increase landing distance by 20% Headwind: A headwind of 10% or your approach speed will decrease landing distance by 20%
CLIMB/ENROUTE/DESCENT •
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Climb Gradient (Feet per NM to Feet per min.): Groundspeed x feet
per NM/60. [Example: (140 kts x 200 ft/nm) ÷ 60 = 466 ft/min] To reduce effects of headwind in climb: Climb at cruise climb To take advantage of tailwind in climb: Climb at Vy Angle of Bank for Standard Rate Turn: 10% of TAS + 5 [example: (120 x .10) + 5 = 17°] Pivotal Altitude: (TAS)²/11.3 (knots) OR (TAS)²/15 (MPH) Time to Station: (60 x Time between bearings)/bearing change = time [Example: (60 x 6 min)/10° = 36 min. to station] Distance to Station: (TAS x Min. flown)/degree of bearing change = distance [Example: (160 x 6 min/10° = 96 miles)] Time to Descend: (Altitude to Lose/Rate of Descent) = Time to Descend Miles to Descend: (Flight Level/3) = NM [Example: (120/3) = 40 NM] 3° Glideslope: Half your ground speed and add a zero [Example: (90 ÷ 2 = 45) x 10 = 450 fpm] Calculating Visual Descent Point (VDP) Distance Method: HAT (height above touchdown)/300 [Example: (480/300) = 1.6 NM from threshold] Calculating Visual Descent Point (VDP) Time Method: HAT x 10% [Example: 480 x 10% = 48 seconds to subtract from MAP timing]
