ATPL Navigation (Sri Lanka CAA Pilot Licence Examinations) flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Great circle distance

The shortest distance between two points on a sphere, measured along the arc of the great circle joining them; in nautical miles it equals 60 times the angular arc in degrees.

Departure formula

Along a parallel of latitude, departure in nautical miles equals change of longitude in minutes multiplied by the cosine of the latitude. It does not apply to great circle legs.

Conversion angle

Half the change of longitude between two meridians. It is the angle between the great circle track and the rhumb line at either end of the route.

Rhumb line

A track crossing every meridian at the same angle. It plots as a straight line on a Mercator chart but is longer than the great circle between the same points.

Mercator scale factor

On a Mercator chart, scale at a given latitude equals the equatorial scale multiplied by the secant of the latitude, so scale increases toward the poles.

Lambert conformal conic

A conical chart on which great circles plot approximately as straight lines and scale is correct on two standard parallels; commonly used for mid-latitude navigation.

Local mean time

Local mean time equals UTC plus longitude divided by 15, with east longitude positive. Every 15 degrees of longitude corresponds to one hour of time difference.

ADF relative bearing

The angle measured clockwise from the aircraft heading to the direction of the NDB. Adding it to heading gives the magnetic bearing to the station, the QDM.

VOR TO/FROM flag

The flag resolves the 180-degree ambiguity of the course deviation indicator. A centered needle with FROM means the aircraft is on the selected radial outbound from the station.

VOR line-of-sight range

VOR range in nautical miles is approximately 1.23 times the square root of the height in feet above the station, using the combined aircraft and station heights.

DME slant range

DME measures the straight-line slant distance to the station, so it always reads greater than the true ground distance, with the largest error directly overhead.

ILS glideslope path

The glideslope is normally set at 3 degrees, giving a descent of about 300 feet per nautical mile along the approach path to the runway.

Marker beacon positions

The outer marker lies about 4 nm from the threshold with a blue 400 Hz signal; the middle marker lies about 3500 ft out with an amber 1300 Hz signal.

GPS fix requirement

A three-dimensional position fix with the receiver clock solved requires signals from at least four satellites; RAIM monitors for faulty signals.

Mode C transponder

A secondary surveillance radar reply that reports the aircraft pressure altitude, encoded so the controller can display altitude alongside the Mode A identity.

Contingency fuel

Fuel carried in addition to trip fuel, commonly 5 percent of trip fuel or a specified time, to cover unforeseen deviations from the planned route or conditions.

Final reserve fuel

For turbine aircraft, holding fuel for 30 minutes at 1500 feet above the alternate aerodrome; it must remain after the approach and landing.

Specific range

Nautical air miles flown per unit of fuel consumed. It reaches its maximum near the speed for maximum lift-to-drag ratio, the best glide speed.

Endurance and range

Endurance in hours equals fuel available divided by fuel flow; range in nautical miles equals endurance multiplied by TAS in still air, then corrected for wind.

Equal time point

The point on track where the time to continue to the destination equals the time to return to the departure or alternate airfield, accounting for wind.

Point of no return

The point where fuel remaining to continue to destination equals fuel needed to return; it depends on wind, fuel remaining, and fuel flow.

In-flight fuel monitoring

Comparing actual fuel flow and ground speed with the flight plan at each waypoint; a sustained negative trend requires recalculating fuel at destination.

QNH versus QFE

QNH set on the subscale makes the altimeter read elevation at the airfield; QFE makes it read zero on the ground. QNE at 1013.25 hPa gives flight level.

Altimeter pressure error

Near the surface, 1 hPa corresponds to about 30 feet. Flying from high to low pressure without resetting the subscale makes the aircraft lower than indicated.

CAS and EAS

Calibrated airspeed is indicated airspeed corrected for position and instrument error; equivalent airspeed is calibrated airspeed corrected for compressibility effect.

Mach number

The ratio of true airspeed to the local speed of sound. The speed of sound depends only on temperature, about 661 knots at ISA sea level.

Rate one turn

A turn of 3 degrees per second, completing 360 degrees in two minutes. Required bank is roughly TAS divided by 10 plus 7 degrees.

Heading indicator drift

The directional gyro drifts from real and apparent precession, so it must be realigned periodically with the magnetic compass in straight, level, unaccelerated flight.

Magnetic compass errors

Acceleration and turning errors are largest on easterly and westerly headings; the compass is unreliable during turns and while accelerating or decelerating.

Centre of gravity formula

Centre of gravity position equals total moment divided by total mass, measured from the datum; each item's moment is its mass multiplied by its arm.

CG shift from moving mass

The shift of the centre of gravity equals the mass moved multiplied by the distance moved, divided by the total mass of the aircraft.

Forward CG limit

The forward limit is set by elevator authority for rotation and landing flare, and by the ability to recover from a stall with available control effectiveness.

Zero-fuel mass

The mass of the aircraft and its contents excluding usable fuel. It must not exceed the certified maximum zero-fuel mass shown in the mass and balance documentation.