General guidelines

Formulas appendixGeneral

Glide path and descent

Formula —

Glide distance (ft) ≈ glidepath angle × 60 × height (ft) — rule of thumb 300 ft per nm at 3°

Formula —

Rate of descent (ft/min) ≈ GS (kt) × 5 at 3° glide path (× 3.5/3 for 3.5°)

Formula —

Glide path (°) = (gradient % × 60) / 100

Turns and load factor

Formula —

Rate 1 bank (approx) = TAS / 10 + 7 (degrees)

Formula —

Radius of turn (NM) = TAS / (π × rate × 60)

Formula —

Load factor n = 1 / cos(bank angle)

Formula —

Stall speed in manoeuvre: Vs new = Vs old × √(n) or Vs new = Vs old × √(W new / W old)

Speed chain

Key fact

IAS → position/instrument error → CAS/RAS → compressibility → EAS → density → TAS

Formula —

EAS = √(relative density) × TAS — e.g. relative density = ¼ at FL400

Formula —

Mach = TAS / LSS

Formula —

LSS (kt) ≈ 38.95 × √(T in Kelvin) — or 661 kt at MSL ISA; 573 kt at tropopause

Bearings (NDB/VOR)

Key fact

VOR variation at station; NDB variation at aircraft. Push the head, pull the tail when intercepting QDR/QDM.

Formula —

QDM ± 180° = QDR | QDR + variation = QTE | Relative bearing + true heading = true bearing

ISA

Key fact

ISA at MSL: 15°C, 1013.25 hPa, 1225 g/m³. Lapse rate 1.98°C/1000 ft to tropopause (~36 000 ft), then -56.5°C constant to 66 000 ft.