Collection of Aviation Formulas
The Most Important Rules of Thumb
Speed
Knots to km/h: (Knots x 2) – 10% = km/h
Altitude
| m -> ft | m * 3.28 | (m * 3) + 10% |
|---|---|---|
| ft -> m | ft / 3.28 | (ft / 3) – 10% |
15,000 = 4.75 km
Distance / Speed
| km -> NM | km / 1.852 | (km / 2) + 10% |
|---|---|---|
| NM (kts) -> km (/h) | NM * 1.852 | (NM x 2) – 10% |
Descent Rate [in ft/min] for 3° Standard Approach
GS [in kts] · 5
| Liters -> US-Gal | Liters / 3.78 | (Liters / 4) + 5% |
|---|---|---|
| US-Gal -> Liters | US-Gal * 3.78 | (US-Gal * 4) - 5% |
92 gal in 348 liters (Full refueling Cirrus SR22)
46 gal in 174 liters (To the tabs - Half refueling Cirrus SR22)
Standard Altitude
15°C @ MSL minus 2°C per 1000ft above MSL
Air pressure MSL: 1013.25 hPa
Cloud Height
| Cloud Height (ft AGL) | Spread (in Kelvin) x 400 |
|---|
Surface and Altitude Wind
500 m AGL: + 20° (up to 30°) (wind veering to the right), wind increases by a factor of 2
1500 m AGL: + 30° (up to 40°) (wind veering to the right), wind increases by a factor of 3
Stall Speed in Turns
| Bank Angle | 0° | 30° | 45° | 60° | 75° |
|---|---|---|---|---|---|
| Factor | 1 | 1.1 | 1.2 | 1.4 | 2.0 |
## True Airspeed (TAS)
Indicated airspeed (IAS) plus 2% of the indication per 1000 ft altitude
Important Formulas for Instrument Flight
Range (NM) = 1.25 x (√height station + √FL(ft)) FL(ft) = (Range(ft) / 1.25 - √height)^2
WCA = Wind Diff Angle x Wind Speed / TAS
RMI: RB = QDM(ADF pointer) - MH negative value + 360
Distance to DME = Altitude ft / 6000 (6000ft = 1 NM above DME)
To NDB -> relative bearing = 0° Away from NDB -> relative bearing = 180°
Slant range = (time (ms) - 50) / 12.36
DMEdist² = (dist_hor)² + height²
Wave length = speed of light (300000km/s) / frequency (Hz)
Rate of Descent = GS x 5 (every 10kt in GS = 50ft/min)
1 : 60 Rule: 60 NM -> 1° = 1NM 100 NM -> 1.5 NM; 5NM in 100 NM = 3°
RMI bearing (compass) -> VAR/DEV -> true bearing
Max Radar Range Range = c / (2 x PRF) OR PRF = c / (2 * Range) c = 3 x 10^8 m/s for m or km c = 162,000 NM/s for NM
GS ILS glide slope out -> LOC (GS out) Headwind = cos(x°) x GS
T ISA = 15° - (FL/10) x 2 (-2° per 1000ft, -0.65° per 100m) 1hPa -> 27ft at MSL, 36ft at 10,000ft, 50ft at 18,000ft, 15m (50ft) at 5500m
QFE from QNH, 27ft = 1hPa, QFE smaller QNH above MSL Temp > ISA -> QNH > QFF (below sea level inverted) QFE above MSL < QNH
Layer thickness = Δ height (ft) + (0.004 x Δ height (ft) x Δ temp (°C)) PA (Altimeter to ISA) + Δ QNH QNHA (Altimeter to QNH) + Δ temp TA (dangerous-Δ, instr. over read) H -> L -> T -> R -> H
PA (Altimeter to ISA)
- Δ QNH
QNHA (Altimeter to QNH)
- Δ temp
TA (dangerous-Δ, instr. over read)
H -> L -> T -> R -> H
ISA 700hPa = FL100 = -5°C ISA 500hPa = FL180 = -21°C ISA 300hPa = FL300 = -45°C
1000ft = 0.305km (ROT: /3 -10%) 1000m = 540NM, 1 km = 0.54NM
Wind 2000ft alt. Direction (veers) +30° Speed x2
t v -> p ^ (density lin. pressure neg. temp)
0° /h (= equator) 30°N - 7.5° /h to R (roughly 1/4) 45°N - 11°/10.5° /h to R 60°N - 13°/h to R 30°S - 7.5° /h to L Max 15°/h at north pole
I AS (indicated on airspeed indicator)
Instrument and Position (absence CAS = IAS)
C AS (Pt - Ps)
Compression (>200kt)
E AS
- Density (fall in temp)
T AS (increases with height)