Rules of Thumb (ROT)

Rules of thumb (ROT) are quick ways / mental aids to calculate a large array of ground and in-flight information which can simplify your life (and let your brain get back to other things).  These are alphabetical.  

See also: Aviation Mnemonics

NOTES:

• CG = climb gradient (FPNM), also degrees nose up from level
• DG = descent gradient (FPNM), also degrees nose down from level 
• DIST = distance
• FPM = feet per minute (vertical speed indicator, this is a RATE & depends on groundspeed)
• FPNM = feet per nautical mile (this is a GRADIENT and doesn't change with groundspeed)
• GS = ground speed (divide GS / 60 to get NMPM)
• HAT = height above touchdown
• MPM = miles per minute (a version of groundspeed [GS])
• NMPM = nautical miles per minute (GS / 60)
• PDP = planned decision point (in conjunction with a visual descent point [VDP])

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• 50/70 Rule (for aborting takeoffs)
• 60-1 rule (probably the most universal)
• Altitude to lose/distance = FPNM (which is also degrees nose down)
• Altitude to lose/time = FPM (which is vertical speed)
• Approaches (in gusty winds):  add half the gust factor to normal final speed
• Civil Twilight:  usually 20-35 after sunset
• Climb gradient
• Climb gradient (FPNM) to climb rate (FPM) using ground speed (GS)
• NMPM x FPNM = FPM (350 FPNM needed @ 80kts = 466 FPM)
• FPNM = DG (angle) x NMPM (GS) x 100
• Course corrections (1 degree is 1 nm at 60 nm from a VOR station)
• Crosswind (estimate)
• 30 degrees off = 50% wind speed
• 45 degrees off = 75% wind speed
• 60 degrees or more off = ~100%
• Descents:
• 1 degree of descent = 100 feet lost in 1 NM (this is gradient)
• When to start?
• 3-6 Rule:  ALT/3 (distance) and 6 x GS (descent rate)
• ALT/FPM x GS (5000’/500 x 1.5 = 15NM)
• ALT/3 (for 3°)  (5000’/3 = 16.67NM).  This is altitude to lose.  
• If you divide by a smaller number, you'll have a painfully slow descent.  With a bigger number, you might get too fast and/or make passengers uncomfortable.
• Degrees = ALT/DIST (3.3° = 10000' / 30 nm)
• Required rate:  ALT/DIST x GS (4900’/7NM x 1.5 = 1050 FPM)
• Glideslope descent rates (for 3 degrees)
• Groundspeed / 2 and add a zero (90 kts = 450 FPM)
• Groundspeed x 5, (120 kts = 600 FPM)
• Remember, this is a RATE not a GRADIENT!
• 3 degree glideslopes always have a 300 FPNM gradient
• Gusty wind approaches:  add half the gust factor to normal final speed
• ILS course width:
• Crossing the threshold, 1/2 dot localizer deflection = about 1/2 the runway width. So a half dot off as you approach the runway, you'll be looking at the runway edge lights
• Landing distance:  10% weight increase = 20% takeoff & landing distance increase
• Master Equation: MPM x FPNM = FPM (or groundspeed x gradient = rate)
• I call this the master equation because it can get you almost anywhere
• PDP = TIME to MAP – (10% of HAT)
• Required rate:  ALT/DIST x GS (4900’/7NM x 1.5 = 1050 FPM)
• Takeoff
• 7 ROT for takeoff performance.
• Abort decision (the 50/70 rule).
• Distance:
• 10% weight increase = 20% takeoff & landing distance increase
• Increases about 10% for every additional 1,000 feet of density altitude
• Summer flying, 3 ROTs.
• Windshear is double peak wind:  if a microburst is 30 kts, you could get 60 kts shear
• VDP (visual descent point)
• FPM = DIST x GS
• HAT/3 = DIST @ 300 FPNM (adjust for DME)

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Other Sites and Resources:

• 5 rules-of-thumb you can use on your next flight.
• 5 rules-of-thumb you can use on your next flight.
• Easy mental math for pilots (boldmethod)
• Questions by Fly the Wing
• Quiz of mental math (boldmethod)

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