CAA NZ Instrument Rating Navigation common mistakes
CAA NZ Instrument Rating Navigation · Understand the traps and how to avoid them.
Computing drift and heading using groundspeed or TAS interchangeably, then applying the result to the wrong leg of the flight plan.
Candidates learn the wind triangle as a single formula and don't keep track of which speed belongs on which vector, especially when the wind is given in degrees true versus magnetic.
What to do instead
Draw the vector triangle every time: TAS along the heading vector, wind vector from the met source, groundspeed along track. Convert wind direction to the same reference (true or magnetic) as the track before solving, and label each vector's speed and direction before calculating.
Mixing true, magnetic, and compass references when converting between track and heading, producing a heading error equal to the variation or deviation.
The exam supplies variation and deviation in different formats (east/west, plus/minus, isogonic notes) and candidates apply the correction in the wrong direction or skip one conversion step.
What to do instead
Use a fixed ladder: True → (apply variation) → Magnetic → (apply deviation) → Compass, and reverse it for the other direction. Write 'east is least' or draw a compass rose for each conversion, and check that the final heading differs from track by a plausible amount.
Calculating time en route and fuel using TAS or an assumed speed instead of the actual groundspeed for each leg, particularly with strong head or tail winds.
Candidates default to the cruise TAS quoted in the flight plan and forget that time and fuel burn depend on groundspeed, which varies with wind on each leg.
What to do instead
Compute groundspeed per leg from the wind triangle, then time = distance ÷ groundspeed. Sum leg times and multiply by hourly fuel flow; add reserve and taxi separately. Cross-check total time against a rough TAS-based estimate to catch gross errors.
Reading a position from lat/long or a bearing/distance fix and reporting it with the wrong format or hemisphere, or transposing minutes and degrees.
Candidates are rushed and the exam mixes formats (degrees/minutes, decimal degrees, bearing/range), so they copy digits without checking the hemisphere or the degree/minute boundary.
What to do instead
Always write latitude first with N/S and longitude second with E/W, and keep minutes below 60. For bearing/distance fixes, state the bearing reference (true or magnetic) and measure distance from the stated origin. Re-read the digits back against the question before answering.
Plotting or interpreting a bearing from a chart without allowing for chart convergence or the difference between grid, true, and magnetic north at the aircraft's position.
On Lambert Conformal or Mercator charts the relationship between grid lines and true north changes across the chart, and candidates apply a single variation value everywhere.
What to do instead
Identify the chart projection and note whether grid lines converge. Use the variation at the aircraft's actual position, not at the departure point, and for grid-referenced charts apply convergence explicitly. Verify by measuring the same line from both ends.
Misapplying the 1-in-60 rule, using the wrong distance or angle, and getting a track error or closing angle that is out by a factor of two or more.
Candidates memorise 'distance off = track error × distance ÷ 60' but plug in the remaining distance instead of the distance flown, or add track error and closing angle incorrectly.
What to do instead
State the rule as: track error (degrees) = 60 × distance off track ÷ distance flown; closing angle = 60 × distance off track ÷ distance remaining. Keep the two distances separate, and use the sum of track error and closing angle for the heading change to the destination.
Treating a VOR radial as a bearing to or from the station without checking whether the CDI shows TO or FROM, or confusing radial with magnetic bearing.
The radial is defined from the station, but the aircraft's heading and the OBS setting interact, and candidates forget that the displayed course is the selected radial, not the aircraft's track.
What to do instead
Remember: a radial is a magnetic bearing from the station. To fly inbound on a radial, set the OBS to that radial and track with a FROM indication; outbound uses the reciprocal with TO. Confirm the TO/FROM flag matches the intended direction before interpreting the deviation.
Ignoring wind effect on the holding pattern or procedure turn, drawing the entry and outbound leg with the same heading as the inbound course.
Candidates treat holds as geometric shapes on paper and forget that wind drift changes the outbound time and the turn direction needed to stay within protected airspace.
What to do instead
Determine the entry (direct, parallel, teardrop) from the aircraft's heading relative to the inbound course, then apply wind correction on the outbound leg and adjust timing so the inbound leg is the specified length. Sketch the pattern with wind arrows before choosing headings.
Using the wrong scale or unit when measuring distance on a chart, or measuring along a straight line when the route follows airways with dog-legs.
Charts mix scales (1:500,000 versus 1:250,000) and candidates measure the direct line rather than summing segment lengths, or use nautical miles when the scale gives statute miles.
What to do instead
Confirm the chart scale and the unit of the scale bar before measuring. Break the route into segments at each waypoint, measure each, and sum. Convert units explicitly (1 nm = 1.852 km) and sanity-check against published leg distances.
Failing to update the dead-reckoning position for elapsed time, wind, and heading changes, then answering a position question with the last known fix.
Candidates treat DR as a one-step calculation and forget that each leg's wind and heading alter the subsequent position, especially after a diversion or a hold.
What to do instead
Maintain a running DR log: for each leg record heading, TAS, wind, groundspeed, time, and distance, and advance the position leg by leg. After any heading or altitude change, recompute groundspeed and drift before plotting the next point.