DGCA CPL Tech Specific cheat sheet

Four-stroke cycle order: induction, compression, combustion (power), exhaust; the crankshaft completes two revolutions per cycle, so each cylinder fires once every two turns.

Valve timing: inlet valve opens before TDC and closes after BDC; exhaust opens before BDC and closes after TDC - overlap improves scavenging and cooling.

Detonation is uncontrolled explosive combustion after normal ignition, raising CHT; pre-ignition is ignition before the spark. Both are countered by richer mixture, lower power, cooler plugs, higher octane.

Mixture ratio: chemically correct is about 15:1 air-to-fuel by mass; best power near 12:1, best economy near 16:1. EGT peaks at approximately the stoichiometric ratio.

Fixed-pitch propeller: blade angle is fixed, so RPM changes with airspeed and power. Constant-speed unit uses a governor with flyweights and a speeder spring to hold selected RPM by varying blade angle.

Hydraulic system: pressure = force/area. A smaller piston area gives higher pressure for the same force; a larger output piston area multiplies force at the cost of travel.

Electrical: aircraft use 28 V DC (24 V battery) or 14 V DC (12 V battery). Alternator output is rectified and regulated; the battery is primarily for starting and standby.

Landing gear: shimmy is damped by nosewheel steering dampers; torque links maintain wheel alignment; micro-switches signal gear-up/down and squat switches inhibit retraction on the ground.

Airframe structures: semi-monocoque skin carries shear and tension, stringers and frames stabilise the skin and carry bending; fail-safe and safe-life designs define inspection/replacement intervals.

Density altitude = pressure altitude + 120 × (OAT − ISA temperature at that level). High density altitude reduces power, thrust and lift and increases take-off and landing distances.

Take-off distance varies roughly with the square of weight for the ground roll; a 10% weight increase raises the ground roll by about 21%.

Rate of climb (ft/min) ≈ (excess power × 33,000)/weight in pounds; climb gradient (%) = (rate of climb in ft/min × 100)/ground speed in ft/min.

Crosswind component = wind speed × sin(angle between wind and runway); headwind component = wind speed × cos(angle). Use the wind triangle or the circular slide rule.

Centre of gravity: CG = Σ(moment)/Σ(weight), where moment = weight × arm. Loading forward of the forward limit increases stability but raises stall speed and elevator forces; aft of the aft limit reduces longitudinal stability.

Stall speed varies with the square root of load factor: Vs(n) = Vs × √n. A 60° bank gives load factor 2, so stall speed rises by about 41%.

Endurance is maximum at the speed for minimum fuel flow per hour; range is maximum at the speed for minimum fuel flow per nautical mile (approximately 1.32 × V for best endurance for a piston aircraft).

Landing distance increases with the square of touchdown speed; a 10% increase in approach speed adds about 21% to the landing roll.

Fuel planning: trip fuel + taxi + contingency + alternate + final reserve; final reserve for a piston aircraft is typically 45 minutes at cruise consumption.

Pitot-static: the ASI compares dynamic pressure (pitot) with static pressure; the altimeter and VSI use static pressure only. A blocked pitot with open static makes the ASI behave like an altimeter.

Altimeter setting: 1 hPa ≈ 27 ft near sea level; 1 inHg ≈ 1,000 ft. Flying from high to low pressure without resetting the subscale reads higher than actual altitude.

VSI is a rate instrument: a calibrated capillary leak delays the capsule response, giving a lag of several seconds; it reads zero in level flight after stabilising.

ASI errors: position (static source) error, instrument error, compressibility error and density error. Only density error is corrected by the TAS calculation.

TAS ≈ IAS × (1 + 0.02 × altitude in thousands of feet) as a rough rule; the precise relation uses density ratio: TAS = IAS/√σ.

Gyroscopes: rigidity in space and precession. A vacuum-driven attitude indicator and heading indicator rely on rigidity; the turn coordinator uses precession and is electrically driven.

Turn coordinator: a standard-rate turn is 3°/s, 180° in one minute, 360° in two minutes. The inclinometer ball shows slip (ball inside) or skid (ball outside).

Magnetic compass: deviation is airframe-induced and shown on the compass card; variation is angular difference between true and magnetic north shown on charts. Acceleration error turns the compass north in the northern hemisphere on acceleration.

Engine instruments: tachometer reads RPM directly or via a generator; CHT and EGT are thermocouples; oil pressure is a direct-reading Bourdon tube or a pressure transducer.

Great circle is the shortest track between two points; rhumb line is a constant-track line. Mercator charts show rhumb lines as straight lines but distort area at high latitude.

1 minute of latitude = 1 nautical mile = 1,852 m. 1 minute of longitude = 1 NM × cos(latitude).

Conversion: track true ± variation = track magnetic; track magnetic ± deviation = track compass. Variation east is least (subtract), variation west is best (add) when converting true to magnetic.

Wind triangle: heading + wind vector = track and groundspeed. Drift = track − heading; use the CRP-5 or E6B for a quick solution.

Time = distance/groundspeed. Fuel = consumption × time. For a diversion, use the one-in-sixty rule: 1 NM off track at 60 NM equals 1° of drift.

NDB/ADF: the ADF needle points to the station relative to aircraft heading; relative bearing + heading = magnetic bearing to the station.

VOR: the CDI shows the selected radial; TO/FROM flag indicates whether the selected course leads to or from the station. A centred needle with a FROM flag means the aircraft is on the selected radial.

ILS: localiser gives lateral guidance, glide path vertical guidance; a 3° glide path gives about 300 ft/NM descent. Marker beacons are at approximately 4 NM (outer), 3,500 ft (middle) and 1,000–1,500 ft (inner).

GNSS: RAIM detects and excludes faulty satellites; the required number of satellites for RAIM availability depends on the phase of flight and geometry.

VHF airband is 118.000–136.975 MHz, with 25 kHz or 8.33 kHz channel spacing. 121.5 MHz is the emergency frequency; 243.0 MHz is its military UHF counterpart.

Phonetic alphabet: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Numbers: each digit spoken separately (e.g. 125.4 = one two five decimal four); FL 350 = flight level three five zero; heading 090 = heading zero nine zero.

Readback is mandatory for clearances, runway assignments, altimeter settings, headings, altitudes, frequencies and transponder codes.

Squelch suppresses receiver noise between transmissions; a too-high setting loses weak signals. The volume control should be set with squelch open, then squelch closed.

Transponder codes: 7700 emergency, 7600 radio failure, 7500 unlawful interference. Mode C reports pressure altitude.

Emergency call: MAYDAY three times for distress, PAN-PAN three times for urgency; state callsign, nature of problem, position, altitude, intentions.

Radio failure in VMC: continue VFR, land at the nearest suitable aerodrome and report. In IMC follow the published lost-communication procedure, squawk 7600 and maintain the last assigned level for the specified period.

Antenna and range: VHF is line-of-sight; range in NM ≈ 1.23 × √(height in feet), so higher altitude increases communication range.

Four-stroke cycle order: induction, compression, combustion (power), exhaust; the crankshaft completes two revolutions per cycle, so each cylinder fires once every two turns.

Valve timing: inlet valve opens before TDC and closes after BDC; exhaust opens before BDC and closes after TDC - overlap improves scavenging and cooling.

Detonation is uncontrolled explosive combustion after normal ignition, raising CHT; pre-ignition is ignition before the spark. Both are countered by richer mixture, lower power, cooler plugs, higher octane.

Mixture ratio: chemically correct is about 15:1 air-to-fuel by mass; best power near 12:1, best economy near 16:1. EGT peaks at approximately the stoichiometric ratio.

Fixed-pitch propeller: blade angle is fixed, so RPM changes with airspeed and power. Constant-speed unit uses a governor with flyweights and a speeder spring to hold selected RPM by varying blade angle.

Hydraulic system: pressure = force/area. A smaller piston area gives higher pressure for the same force; a larger output piston area multiplies force at the cost of travel.

Electrical: aircraft use 28 V DC (24 V battery) or 14 V DC (12 V battery). Alternator output is rectified and regulated; the battery is primarily for starting and standby.

Landing gear: shimmy is damped by nosewheel steering dampers; torque links maintain wheel alignment; micro-switches signal gear-up/down and squat switches inhibit retraction on the ground.

Airframe structures: semi-monocoque skin carries shear and tension, stringers and frames stabilise the skin and carry bending; fail-safe and safe-life designs define inspection/replacement intervals.

Density altitude = pressure altitude + 120 × (OAT − ISA temperature at that level). High density altitude reduces power, thrust and lift and increases take-off and landing distances.

Take-off distance varies roughly with the square of weight for the ground roll; a 10% weight increase raises the ground roll by about 21%.

Rate of climb (ft/min) ≈ (excess power × 33,000)/weight in pounds; climb gradient (%) = (rate of climb in ft/min × 100)/ground speed in ft/min.

Crosswind component = wind speed × sin(angle between wind and runway); headwind component = wind speed × cos(angle). Use the wind triangle or the circular slide rule.

Centre of gravity: CG = Σ(moment)/Σ(weight), where moment = weight × arm. Loading forward of the forward limit increases stability but raises stall speed and elevator forces; aft of the aft limit reduces longitudinal stability.

Stall speed varies with the square root of load factor: Vs(n) = Vs × √n. A 60° bank gives load factor 2, so stall speed rises by about 41%.

Endurance is maximum at the speed for minimum fuel flow per hour; range is maximum at the speed for minimum fuel flow per nautical mile (approximately 1.32 × V for best endurance for a piston aircraft).

Landing distance increases with the square of touchdown speed; a 10% increase in approach speed adds about 21% to the landing roll.

Fuel planning: trip fuel + taxi + contingency + alternate + final reserve; final reserve for a piston aircraft is typically 45 minutes at cruise consumption.

Pitot-static: the ASI compares dynamic pressure (pitot) with static pressure; the altimeter and VSI use static pressure only. A blocked pitot with open static makes the ASI behave like an altimeter.

Altimeter setting: 1 hPa ≈ 27 ft near sea level; 1 inHg ≈ 1,000 ft. Flying from high to low pressure without resetting the subscale reads higher than actual altitude.

VSI is a rate instrument: a calibrated capillary leak delays the capsule response, giving a lag of several seconds; it reads zero in level flight after stabilising.

ASI errors: position (static source) error, instrument error, compressibility error and density error. Only density error is corrected by the TAS calculation.

TAS ≈ IAS × (1 + 0.02 × altitude in thousands of feet) as a rough rule; the precise relation uses density ratio: TAS = IAS/√σ.

Gyroscopes: rigidity in space and precession. A vacuum-driven attitude indicator and heading indicator rely on rigidity; the turn coordinator uses precession and is electrically driven.

Turn coordinator: a standard-rate turn is 3°/s, 180° in one minute, 360° in two minutes. The inclinometer ball shows slip (ball inside) or skid (ball outside).

Magnetic compass: deviation is airframe-induced and shown on the compass card; variation is angular difference between true and magnetic north shown on charts. Acceleration error turns the compass north in the northern hemisphere on acceleration.

Engine instruments: tachometer reads RPM directly or via a generator; CHT and EGT are thermocouples; oil pressure is a direct-reading Bourdon tube or a pressure transducer.

Great circle is the shortest track between two points; rhumb line is a constant-track line. Mercator charts show rhumb lines as straight lines but distort area at high latitude.

1 minute of latitude = 1 nautical mile = 1,852 m. 1 minute of longitude = 1 NM × cos(latitude).

Conversion: track true ± variation = track magnetic; track magnetic ± deviation = track compass. Variation east is least (subtract), variation west is best (add) when converting true to magnetic.

Wind triangle: heading + wind vector = track and groundspeed. Drift = track − heading; use the CRP-5 or E6B for a quick solution.

Time = distance/groundspeed. Fuel = consumption × time. For a diversion, use the one-in-sixty rule: 1 NM off track at 60 NM equals 1° of drift.

NDB/ADF: the ADF needle points to the station relative to aircraft heading; relative bearing + heading = magnetic bearing to the station.

VOR: the CDI shows the selected radial; TO/FROM flag indicates whether the selected course leads to or from the station. A centred needle with a FROM flag means the aircraft is on the selected radial.

ILS: localiser gives lateral guidance, glide path vertical guidance; a 3° glide path gives about 300 ft/NM descent. Marker beacons are at approximately 4 NM (outer), 3,500 ft (middle) and 1,000–1,500 ft (inner).

GNSS: RAIM detects and excludes faulty satellites; the required number of satellites for RAIM availability depends on the phase of flight and geometry.

VHF airband is 118.000–136.975 MHz, with 25 kHz or 8.33 kHz channel spacing. 121.5 MHz is the emergency frequency; 243.0 MHz is its military UHF counterpart.

Phonetic alphabet: Alfa, Bravo, Charlie, Delta, Echo, Foxtrot, Golf, Hotel, India, Juliett, Kilo, Lima, Mike, November, Oscar, Papa, Quebec, Romeo, Sierra, Tango, Uniform, Victor, Whiskey, X-ray, Yankee, Zulu.

Numbers: each digit spoken separately (e.g. 125.4 = one two five decimal four); FL 350 = flight level three five zero; heading 090 = heading zero nine zero.

Readback is mandatory for clearances, runway assignments, altimeter settings, headings, altitudes, frequencies and transponder codes.

Squelch suppresses receiver noise between transmissions; a too-high setting loses weak signals. The volume control should be set with squelch open, then squelch closed.

Transponder codes: 7700 emergency, 7600 radio failure, 7500 unlawful interference. Mode C reports pressure altitude.

Emergency call: MAYDAY three times for distress, PAN-PAN three times for urgency; state callsign, nature of problem, position, altitude, intentions.

Radio failure in VMC: continue VFR, land at the nearest suitable aerodrome and report. In IMC follow the published lost-communication procedure, squawk 7600 and maintain the last assigned level for the specified period.

Antenna and range: VHF is line-of-sight; range in NM ≈ 1.23 × √(height in feet), so higher altitude increases communication range.