GCAA ATPL Theory cheat sheet

ICAO Annex 2 (Rules of the Air) applies over the high seas and to all contracting states; national AIP differences must be consulted before flight.

VMC minima in Class C airspace at/above 10,000 ft AMSL: 8 km flight visibility, 1500 m horizontal and 1000 ft vertical distance from cloud.

Class A airspace is IFR only; Class F is advisory IFR/VFR with no ATC clearance required but flight information service provided.

Semi-circular rule (IFR, above 3000 ft AGL, magnetic track): 000-179 use odd flight levels, 180-359 use even flight levels.

Squawk 7700 = emergency, 7600 = radio failure, 7500 = unlawful interference.

Transition altitude is published per aerodrome; above the transition level, altimeter is set to standard pressure 1013.25 hPa.

EASA/ICAO crew duty: minimum rest is at least as long as preceding duty and never less than 10 hours in a 24-hour period.

Emergency frequency is 121.5 MHz; distress call 'MAYDAY' (×3), urgency call 'PAN-PAN' (×3).

DC generator paralleling requires equal voltage and droop compensation; a reverse-current relay/cut-out prevents battery discharge through the generator.

Bleed air for air-conditioning is normally tapped from the HP compressor (around stage 8-12); engine anti-ice uses the same source.

Hydraulic system colour coding: green/blue/yellow systems on Airbus; each has its own reservoir, pump and priority valve.

Fire detection uses thermocouples (engine) or continuous-loop (kidde) sensors; a fire bottle typically discharges halon 1301.

Fuel: Jet A-1 flash point ≈ 38 °C, freezing point ≈ −47 °C; water in fuel is drained at the lowest sump point pre-flight.

Battery capacity is expressed in Ah at the 1-hour rate; NiCd batteries require a deep-cycle to remove memory effect.

Landing gear: oleo strut uses nitrogen over hydraulic fluid; shimmy damper prevents nose-wheel oscillation.

Emergency equipment: portable oxygen (diluter-demand) supplies 100 % above FL 350; PBE lasts about 15-20 minutes.

Altimeter error: if QNH set at high altitude aerodrome, subscale error occurs; below transition, use QNH; above, use 1013.25 hPa (QNE).

ASI uses pitot (total) pressure and static pressure; blockage of the static port causes ASI to over-read in climb and under-read in descent.

Turn indicator shows rate of turn (2 min/360° = rate 1 = 3°/s); turn coordinator also shows rate of roll.

Attitude indicator uses a gyro with 2 degrees of freedom (vertical spin axis); it is earth-referenced and subject to real/apparent wander.

Heading indicator (directional gyro) precesses ~15°/hour due to Earth's rotation; must be realigned with magnetic compass periodically.

VSI measures rate of change of static pressure through a calibrated leak; lag causes over/under-read during abrupt manoeuvres.

Radio altimeter uses frequency-modulated continuous wave (FMCW) in the 4.2-4.4 GHz band; gives height above terrain up to ~2500 ft.

EFIS colour conventions: red = warning, amber = caution, green = normal/engaged, white = status, cyan = advisory.

Mass = volume × density; fuel density Jet A-1 ≈ 0.78-0.80 kg/L, Avgas 100LL ≈ 0.72 kg/L.

CG position: x_cg = Σ(m_i × x_i) / Σ m_i, where x_i is arm from datum.

MTOM ≥ MLM ≥ MZFM; MZFM = MTOM − trip fuel − taxi fuel (approximately).

Underload = allowable traffic load − actual traffic load; allowable = MTOM − DOW − fuel.

Moving a mass m by distance d shifts the CG by Δx = (m × d) / total mass.

Forward CG increases stall speed and elevator effectiveness but reduces cruise performance; aft CG reduces longitudinal stability.

Load sheet: DOW (dry operating weight) + traffic load = ZFW; ZFW + fuel = TOW; TOW − trip fuel = LW.

Floor loading limit is expressed in kg per unit area; exceeding it may damage the cargo floor even below MTOM.

V1 is decision speed: below V1, reject; above V1, continue take-off. V1 must allow stopping within TODA and rotation to V2 by 35 ft.

Balanced field length: V1 chosen so that accelerate-stop distance equals accelerate-go distance to 35 ft.

V2 ≥ 1.13 V_S1 (or 1.08 V_S1 in some cases); V_R ≈ 1.05-1.1 V_MC.

Take-off distance required must not exceed TODA; TODA = TORA + clearway (≤ 1.5 × TORA).

ASDA = TORA + stopway; landing distance available (LDA) may be shorter than TORA.

Climb gradients (CS-25): 2nd segment 2.4 % (twin), 3rd segment 1.2 %, missed approach 2.1 % (twin).

Density altitude = pressure altitude + 120 × (OAT − ISA temp at that level); performance degrades ~1 % per 1000 ft DA.

Headwind increases climb gradient for a given mass; tailwind reduces it; use wind correction from the AFM.

Trip fuel = fuel from take-off to landing at destination; taxi fuel, contingency (5 %), alternate and final reserve (30 min) are additional.

PIC must ensure fuel on board ≥ taxi + trip + contingency + alternate + final reserve + extra.

PLog: leg time = distance / groundspeed; fuel = time × fuel flow; check points at each waypoint.

Equal time point (ETP): point where time to A equals time to B, considering wind; used for diversion planning.

Point of no return (PNR): distance where fuel to return equals fuel to continue; depends on fuel available and consumption.

ISA temperature at altitude = 15 − 1.98 × (altitude in thousands of ft); pressure altitude = indicated altitude with 1013 set.

Wind triangle: GS = TAS × cos(drift) ± wind component; drift = arcsin((W/V) × sin(wind angle)).

Fuel density check: mass = volume × SG; refuelling cross-check against dip tables to detect uplift discrepancy.

Hypoxia: symptoms begin around 10,000 ft; time of useful consciousness at FL 350 is 30-60 s (without oxygen).

Barotrauma: middle ear equalisation via Valsalva; sinus block prevents equalisation, causing pain on descent.

Night vision relies on rods (scotopic vision); use off-centre viewing (10-20° from target) to detect dim objects.

Spatial disorientation: somatogravic illusion (false climb/descent), Leans illusion, Coriolis illusion during head movement under acceleration.

Carbon monoxide binds haemoglobin ~200-250× more strongly than oxygen; symptoms include headache, confusion, cherry-red skin.

Circadian rhythm: body temperature minimum ~04:00-06:00, performance lowest then; jet lag requires ~1 day per time zone to adapt.

G-LOC occurs at sustained +G above ~5 G without anti-G suit; A-LOC is partial loss of consciousness with confusion.

Stress and fatigue: use IMSAFE (Illness, Medication, Stress, Alcohol, Fatigue, Emotion) as a pre-flight self-check.

ISA: sea level 15 °C, 1013.25 hPa, temperature lapse rate 1.98 °C/1000 ft up to 36,090 ft (tropopause).

QNH is pressure reduced to sea level; QFE is pressure at aerodrome level; QNE = 1013.25 hPa.

Pressure altitude = indicated altitude corrected to 1013.25; density altitude = pressure altitude corrected for temperature.

Cloud base estimate: (temperature − dew point) × 400 ft (or ×125 m) gives the convective cloud base.

Stability: stable air gives layered cloud and steady precipitation; unstable air gives cumuliform cloud, showers and turbulence.

Wind veers with height in the northern hemisphere (Ekman spiral); backing is anticlockwise shift.

Icing: clear ice from large supercooled droplets (−0 to −10 °C), rime ice from small droplets; use anti-ice before entering.

Thunderstorm life cycle: cumulus (updrafts), mature (updrafts + downdrafts, hail, lightning), dissipating (downdrafts).

Great circle is the shortest path on a sphere; rhumb line maintains constant track and is longer except along meridians/equator.

1 minute of latitude = 1 nautical mile; 1 minute of longitude = 1 NM × cos(latitude).

Mercator chart: rhumb line is a straight line; scale increases with latitude; used for plotting.

Lambert conformal conic: great circle is approximately a straight line; used for mid-latitude charts.

Conversion angle ≈ ½ × change in longitude × sin(mean latitude) for great circle vs rhumb line.

Track (T) = heading (H) + drift; drift = arcsin((W/V) × sin(angle between track and wind)).

Time zone: 15° of longitude = 1 hour; UTC = local mean time + longitude/15 (east positive).

Magnetic variation: east variation is subtracted from true to get magnetic; isogonal lines connect equal variation.

VOR: 108-117.95 MHz, line-of-sight; radial = magnetic bearing from station; CDI centred with TO/FROM flag.

NDB/ADF: 190-1750 kHz; ADF needle points to station; coastal refraction and night effect degrade accuracy.

DME: 960-1215 MHz; slant range; indicated distance ≈ ground distance + (altitude² / (2 × ground distance)).

ILS: localiser 108-112 MHz (VHF), glideslope 329-335 MHz (UHF); CAT I decision height 200 ft, RVR 550 m.

Glideslope is normally 3°; at 3° the descent rate ≈ 5 × groundspeed (knots) ft/min.

GPS: 24+ satellites in 6 orbital planes; position needs ≥ 4 satellites; RAIM checks integrity.

RNAV/GNSS approach minima depend on SBAS (LPV) or baro-VNAV; LNAV/VNAV minima differ.

Radar: primary returns from skin paint; secondary uses transponder codes; transponder reply on 1090 MHz.

Take-off briefing: rejected take-off call 'STOP', V1 call, engine failure actions, emergency return considerations.

Sterile cockpit: no non-essential activity below 10,000 ft or during taxi, take-off, approach and landing.

Approach briefing: type of approach, minima, missed approach, go-around callouts, runway conditions.

Altimeter cross-check: three altimeters within 75 ft (or company tolerance) before IFR approach.

De-icing/anti-icing holdover time depends on precipitation type, temperature and fluid; re-check before take-off.

Emergency descent: oxygen masks on, squawk 7700, descend to 10,000 ft or MSA, broadcast on 121.5 MHz.

Runway incursion prevention: read back hold-short instructions; use 'line up and wait' only when cleared.

Volcanic ash: avoid; if encountered, reduce thrust, turn 180°, and report to ATC.

Lift = ½ ρ V² S C_L; induced drag = C_L² / (π × AR × e) × ½ ρ V² S.

Stall occurs at critical angle of attack, independent of speed, mass, or bank angle (though stall speed rises with mass and load factor).

Load factor n = L/W; stall speed increases by √n in a level turn (n = 1/cos(bank)).

Induced drag decreases with speed; parasite drag increases with V²; total drag minimum at L/D max.

Sweepback delays Mach buffet but reduces lift coefficient and causes Dutch roll tendency.

Dihedral gives lateral stability (roll due to sideslip); anhedral used on some high-wing aircraft.

Critical Mach number is the free-stream Mach at which local airflow first reaches M = 1; shock stall follows.

Wing tip vortices: strongest when heavy, clean and slow; wake turbulence separation depends on leader/follower weight classes.