CAA NZ PPL Meteorology common mistakes
CAA NZ PPL Meteorology · Understand the traps and how to avoid them.
Reading the QNH off the area chart and using it directly as the pressure setting without checking whether the aerodrome elevation is high enough that QFE or a different chart value applies, then computing density altitude from the wrong base pressure.
Candidates memorise 'QNH is the pressure setting that makes the altimeter read elevation at the aerodrome' but never practise converting between QNH, QFE and QNE, so under exam pressure they grab the first pressure number they see on a chart or METAR.
What to do instead
Before answering any pressure question, write down the three definitions from memory and label which one the stem asks for. Practise a fixed routine: QNH = elevation on the subscale; QFE = zero on the subscale; QNE = 1013.2 hPa with the altimeter reading pressure altitude. Work through at least ten conversion drills where you are given elevation and QNH and must derive QFE, and vice versa, until the direction of each conversion is automatic.
Treating the METAR visibility group as the only visibility that matters and ignoring the forecast visibility, cloud base and weather in the TAF when judging whether a flight can be conducted under VFR.
The METAR is a snapshot that feels concrete and easy to read, while the TAF requires interpreting change groups (BECMG, TEMPO, FM) and validity periods. Candidates default to the observation because it needs less interpretation.
What to do instead
Build a habit of reading every TAF in a fixed order: validity period, wind, visibility, weather, cloud, then each change group with its time window. For each change group, state aloud whether the worst case in that window would still permit the planned VFR flight. Do timed exercises where the METAR is fine but the TAF TEMPO takes the aerodrome below VFR minima, and practise spotting that trap.
Assuming a forecast of 'fine' or high pressure means no significant weather, and failing to identify the frontal or trough feature on the synoptic chart that will actually bring the weather.
Candidates learn pressure systems as isolated facts (high = good, low = bad) rather than as a three-dimensional pattern, so they miss that a cold front embedded in a trough can produce squally showers and wind shifts even when the isobars look unremarkable.
What to do instead
For every synoptic chart question, first locate the fronts and the troughs, then describe the wind shift, temperature change and cloud sequence associated with each. Practise drawing the cross-section of a warm front and a cold front from memory, including cloud types and precipitation zones, and match each to the weather you would expect at the surface.
Calculating density altitude by adjusting only for elevation and temperature, forgetting that low pressure also raises density altitude, or applying the temperature correction in the wrong direction.
The standard rule of thumb ('add 120 ft per degree above ISA') is learned as a mantra without the underlying reason, so candidates misapply it when the question gives a non-standard pressure or an unusually cold day.
What to do instead
Always compute in two explicit steps: pressure altitude first (elevation corrected for the pressure difference from 1013.2 hPa at 30 ft per hPa), then temperature correction to that pressure altitude. Write both numbers down before choosing an answer. Practise with cold-day and low-pressure cases so you see density altitude fall as well as rise.
Interpreting wind direction given in a METAR or TAF as magnetic and comparing it directly with a runway magnetic heading without converting, or misreading the degrees as the direction the wind is blowing towards.
Aviation weather reports give wind direction in degrees true, while runways and ATIS use magnetic. Candidates conflate the two because the numbers look identical in format, and the 'from' versus 'towards' convention is easy to invert under time pressure.
What to do instead
Adopt a rule you say to yourself every time: 'METAR/TAF wind is true and is the direction it comes from.' Convert to magnetic using the local variation before comparing with runway headings. Drill with a set of reports where variation is significant (for example 20 degrees east) so the conversion changes the crosswind component and the favoured runway.
Reading the freezing level from a chart or forecast and assuming that is the only altitude at which airframe icing can occur, ignoring the possibility of supercooled water in cloud above or below that level.
The freezing level is a clean, memorable number, so candidates treat it as a hard boundary. In reality icing is most likely in cloud just above the freezing level where supercooled droplets exist, and in freezing rain below it.
What to do instead
Learn the icing risk bands: clear ice in large supercooled droplets (typically in cumuliform cloud, around 0 to minus 10 degrees Celsius), rime ice in smaller droplets (stratiform, minus 10 to minus 20), and the danger of freezing rain beneath a warm layer. When a question gives a temperature profile, identify every layer where the temperature is between 0 and minus 20 and where cloud is forecast, and treat that as the icing zone.
Answering thunderstorm questions by listing hazards generically (turbulence, icing, hail) without linking each hazard to the specific part of the storm or the specific stage of development where it occurs.
Candidates memorise a hazard list from a summary table rather than the life cycle of the storm, so they cannot distinguish the mature stage from the dissipating stage or explain why the gust front and microburst occur where they do.
What to do instead
Draw the three-stage life cycle from memory and annotate each stage with its dominant hazard: updraught and building cumulus, then mature stage with hail, lightning, heavy rain, gust front and downburst, then dissipating stage with stratiform rain. For each hazard, state whether it is found under the cloud base, at the anvil, or ahead of the storm, and practise questions that ask where a hazard is most likely rather than whether it exists.
Using the mountain wave or lee turbulence rule only when the wind is exactly perpendicular to the ridge, and failing to recognise that strong winds within about 30 degrees of perpendicular still produce severe rotor and wave activity.
Textbook diagrams show wind at right angles to the ridge, so candidates treat the perpendicular case as the only dangerous one and dismiss a 20 to 30 degree offset as safe.
What to do instead
Learn the conditions for mountain wave as a set: wind speed above about 20 knots at ridge level, direction within 30 degrees of perpendicular, and a stable layer near the ridge with less stable air above. For any question giving wind direction and ridge orientation, compute the offset angle first, then decide. Also revise the visual signatures: lenticular cloud, cap cloud, rotor cloud and the marked dowraught on the lee side.
Confusing the definitions of visibility groups in a METAR, such as reporting 9999 as unlimited visibility, or treating RVR as the same as meteorological visibility, and then selecting an answer based on the wrong quantity.
The coded groups are learned by pattern matching rather than by definition, so the distinctions between prevailing visibility, minimum visibility, RVR and vertical visibility blur under exam conditions.
What to do instead
Write out each term with its definition and units: prevailing visibility in metres (9999 meaning 10 km or more), minimum visibility with its direction, RVR in metres for a specific runway, and vertical visibility (VV) as the height of the indefinite ceiling. Then decode a set of ten real METARs by hand, labelling each group, until the codes are read as meanings rather than as strings.
Planning a cross-country by looking only at the terminal forecast for the departure and destination aerodromes, without checking the area forecast, the freezing level, the upper winds and the trend over the whole route and duration of the flight.
Candidates treat the TAF as the whole weather picture because it is the most familiar product, and they forget that en route conditions, terrain and the forecast trend after the planned arrival time are equally part of the decision.
What to do instead
Use a fixed pre-flight checklist every time: area forecast and significant weather chart, TAFs for departure, destination and alternate, upper winds and temperatures for the planned levels, freezing level, and the trend beyond the planned arrival time. Practise with a route crossing a range where the destination TAF is fine but the area forecast shows low cloud and strong wind on the ridge, and decide what the correct go/no-go reasoning is.