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
  • 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, when to abort (the 50/70 rule)
  • Takeoff distance:
    • 10% weight increase = 20% takeoff & landing distance increase
    • Increases about 10% for every additional 1,000 feet of density altitude
  • 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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