CAA NZ Instrument Rating Navigation flashcards

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

Track versus heading

Track is the path the aircraft actually makes over the ground. Heading is the direction the nose points. The difference is drift, caused by wind, and is corrected by a wind correction angle.

Wind correction angle

The angle between heading and track needed to counter drift. Computed with the wind triangle: crosswind component divided by TAS, then converted to degrees using the 1-in-60 rule.

1-in-60 rule

A 1 NM lateral displacement at 60 NM subtends about 1 degree. It converts off-track distance and distance to go into track error and closing angle in degrees.

Closing angle

The heading change needed to regain track after an off-track fix. Equals off-track distance divided by distance remaining, multiplied by 60. Add the original track error for total correction.

Groundspeed calculation

Groundspeed equals TAS plus the tailwind component or minus the headwind component. Component equals wind speed multiplied by the cosine of the angle between wind and track.

Crosswind component

The part of the wind acting across track. Equals wind speed multiplied by the sine of the angle between wind direction and track. At 30 degrees it is about half the wind speed.

Point of no return

The point where time to continue equals time to return. Distance from departure equals endurance multiplied by outbound groundspeed, divided by the sum of outbound and return groundspeeds.

Radius of action

The maximum distance an aircraft can fly from base and return with fuel remaining. Equals endurance times outbound groundspeed times return groundspeed, divided by the sum of both groundspeeds.

Pressure altitude

Altitude indicated when the subscale is set to 1013.25 hPa. Approximated from elevation by adding 30 ft for each hPa the QNH is below 1013, or subtracting when above.

True altitude from QNH

Indicated altitude corrected for pressure and temperature error. Add about 30 ft per hPa when QNH exceeds 1013, and about 120 ft per degree Celsius above ISA.

Density altitude

Pressure altitude corrected for temperature. Approximately pressure altitude plus 120 times the difference between outside air temperature and ISA temperature at that level.

True airspeed estimate

TAS increases about 2 percent per 1000 ft of altitude for a given IAS. At 10 000 ft, TAS is roughly 20 percent higher than indicated airspeed in still air.

Speed of sound

About 661 kt at sea-level ISA, falling with temperature. Approximated as 38.97 times the square root of absolute temperature in kelvin, giving the local Mach number divisor.

ISA temperature lapse

Standard atmosphere assumes 15 degrees Celsius at sea level and 1013.25 hPa, decreasing 1.98 degrees Celsius per 1000 ft up to the tropopause at about 36 090 ft.

Magnetic variation conversion

Variation east means magnetic is least: subtract easterly variation from true to get magnetic. Variation west means magnetic is best: add westerly variation to true.

NZTM2000 grid

The New Zealand Transverse Mercator 2000 projection used on current topographical charts. Positions from GNSS in WGS84 must be converted before plotting on NZTM charts.

WAC chart scale

World Aeronautical Charts are 1:1 000 000. One centimetre on the chart represents 10 km on the ground, and one inch represents about 13.7 NM.

Topographical map scale

A 1:50 000 map shows 1 cm as 500 m on the ground. A 1:250 000 map shows 1 cm as 2.5 km. Scale choice depends on the navigation task.

RAIM prediction

Receiver Autonomous Integrity Monitoring checks whether enough satellites with adequate geometry are available for the approach. A prediction must be run for the planned arrival time and procedure.

RNP APCH minima

New Zealand GNSS approaches are published as RNP APCH. LNAV is non-precision, while LNAV/VNAV and LPV provide vertical guidance and lower minima.

Minimum safe altitude

The lowest altitude providing obstacle clearance within a defined area, often a 25 NM sector around a navigation aid. It does not guarantee radio or navigation reception.

Descent rate for gradient

Rate of descent in feet per minute equals groundspeed in knots multiplied by gradient in feet per nautical mile, divided by 60. A 3 degree path is about 318 ft/NM.

Top of descent distance

For a 3 degree path, distance in nautical miles is roughly altitude to lose in feet divided by 300. Use groundspeed, not TAS, to convert this to a descent rate.

Fuel reserve requirement

New Zealand IFR flights normally carry 30 minutes holding fuel plus approach and missed approach fuel, plus any contingency required by the operator or AIP.

Equal-time point

The point along track where time to destination equals time back to departure. Uses the same formula as point of no return but with fuel available to that point.

Drift from two fixes

Compare the fix with the dead reckoning position to find track error and groundspeed error. Apply the correction to the remaining legs rather than the leg already flown.

Direct-to terrain check

Before accepting a direct clearance, compare the new track with charted minimum safe altitudes and terrain. A direct track may leave the protected area of the planned route.

Alternate minima for GNSS

A GNSS approach may be used as an alternate only if the plate and AIP permit it and RAIM is predicted available. Baro-VNAV minima have additional temperature limits.

Heading to intercept track

To intercept a track, fly a heading that closes the angle at a sensible rate. Use the 1-in-60 rule to set an intercept angle of roughly 30 degrees for close-in intercepts.

Time enroute calculation

Time in minutes equals distance in nautical miles divided by groundspeed in knots, multiplied by 60. Always use groundspeed, not TAS, for leg timing.

Unit conversions

One nautical mile equals 1.852 kilometres or 1.15078 statute miles. One knot is one nautical mile per hour, about 0.514 metres per second.

QNH versus QFE

QNH set on the subscale gives altitude above mean sea level. QFE gives height above the aerodrome reference point. Instrument approach minima in New Zealand use QNH.

Mach number

The ratio of true airspeed to the local speed of sound. Because the speed of sound falls with temperature, a constant TAS gives a higher Mach number at high altitude.