Meteo, instruments & comms

Formulas appendix050 / 022 / 090

050 Meteorology

Formula —

DALR = 3°C/1000 ft | SALR ≈ 1.8°C/1000 ft (temperate, not constant)

Formula —

Height rule of thumb: S.L. 1013 hPa ≈ 27 ft/mb | 18 000 ft ≈ 500 hPa ≈ 48 ft/mb

Formula —

Föhn temperature rise = (lee cloud base − windward cloud base) × 1.2

Key fact

ELR greater than DALR = absolutely unstable | ELR less than SALR = stable | Between = conditionally unstable.

Formula —

Geostrophic wind — PGF balanced by Coriolis: GF = 2ωηv sin(lat)

022 Instrumentation

Formula —

Rate 1 turn = 180°/min (3°/s) | Bank for rate 1 ≈ TAS/10 + 7

Formula —

Latitude nut wander = 15 × sin(lat) °/hr (NH +) | Earth rotation wander = 15 × sin(lat) °/hr (NH −)

Formula —

Transport wander ≈ (GS × tan(lat)) / 60 — NH: E negative, W positive

Formula —

Total compass deviation = A + B sin(heading) + C cos(heading)

Key fact

TAT = SAT + ram rise | Blocked pitot → ASI over-reads | Blocked static → ASI under-reads in climb.

090 Communications

Formula —

VHF range (NM) ≈ 1.25√(Tx height) + 1.25√(Rx height) — line of sight

Formula —

Wavelength λ = c / f | Skip distance (NM) ≈ 1.43 × √(ionosphere height km)

Key fact

VHF = 118–137 MHz, AM, vertically polarised. HF long range 2.85–22 MHz. Speed of light ≈ 300 000 km/s.