NCAA PPL Flight Performance & Planning common mistakes
NCAA PPL Flight Performance & Planning · Understand the traps and how to avoid them.
Using the published empty mass and empty-arm figures from the aircraft flight manual instead of the aircraft's actual current empty mass and moment from its latest weighing record, then adding payload and fuel on top of that baseline.
Candidates memorise a 'typical' empty mass for the type or copy it from the sample loading in a textbook, forgetting that every airframe drifts from the nominal figure through equipment changes, repairs, paint, and interior modifications, and that the current weighing report supersedes the manual sample.
What to do instead
Before any calculation, locate the most recent weighing record in the aircraft documents and transcribe the empty mass and empty moment (or empty arm) exactly as recorded. Recompute the empty moment as mass times arm rather than reusing a manual figure, and state in your working that the source is the current weighing report, not the AFM sample.
Reading the CG envelope graph by plotting the takeoff mass and then declaring the loading acceptable, without separately checking the zero-fuel or landing condition where the CG can sit outside limits.
The heaviest or most forward condition is not automatically the critical one; with fuel in wing tanks or a rear baggage load burned off, the zero-fuel CG can move aft or forward out of the envelope even when takeoff and landing masses are inside. Candidates treat the envelope as a single check rather than a set of conditions.
What to do instead
Plot at least three points on the same envelope: zero fuel, takeoff, and landing, each with its own mass and total moment. If any point falls outside, redistribute load (move baggage, shift passengers, reduce fuel) and re-plot all three. Show each point labelled on the chart extract you draw in your working.
Adding masses arithmetically but averaging arms, or adding arms directly, instead of summing moments and dividing total moment by total mass.
The CG formula is a weighted average, and candidates under time pressure treat arm as if it were a simple additive quantity, especially when several items share a compartment or when converting between inches and metres mid-calculation.
What to do instead
Build a table with columns for item, mass, arm, and moment, compute every moment as mass times arm, sum the moment column, then divide by summed mass. Convert all arms to one unit before multiplying, and sanity-check the answer: the final CG must lie between the smallest and largest arm in the table.
Treating the runway distance chart as a single reading, ignoring that the plotted distances assume a specific flap setting, a dry paved surface, sea level pressure altitude, ISA temperature, zero wind, and a particular obstacle clearance.
The chart's headline number is memorable and the correction notes are small print, so candidates quote the base figure as the answer and skip the headwind, slope, and temperature adjustments, or apply them in the wrong direction.
What to do instead
Write down the assumed conditions printed on the chart before reading any value, then apply each correction in the order the chart specifies: pressure altitude, temperature, wind component, runway slope, and surface. State the direction of each correction explicitly (headwind decreases distance, tailwind increases it) so an inverted sign is visible in your working.
Mixing up pressure altitude and density altitude, or using field elevation in place of pressure altitude when entering the performance chart.
Both are 'altitudes' in feet and the difference only matters on hot or high-pressure days, so candidates substitute one for the other and then also forget the temperature correction, effectively double-counting or omitting the density effect.
What to do instead
Compute pressure altitude first as elevation plus (standard pressure minus actual pressure) times 30 feet per hectopascal (or the millibar-to-feet factor your syllabus uses), then enter the chart at that value. Use density altitude only where the chart or question explicitly asks for it, and keep the two calculations on separate lines of your working.
Using the forecast surface wind instead of the runway-specific headwind or crosswind component, and forgetting to interpolate between the tabulated angles.
The wind given in a briefing is usually reported in degrees and knots relative to true or magnetic north, and candidates either subtract angles incorrectly or take the full wind speed as the headwind, which understates takeoff and landing distance and overstates crosswind capability.
What to do instead
Convert the wind direction into a difference from runway heading, take the sine for crosswind and cosine for headwind, and check the result against the aircraft's demonstrated crosswind limit. Where the manual tabulates components by angle, interpolate linearly between the bracketing columns and record both the angle difference and the resulting components.
Planning fuel as a single block figure and not separating taxi, trip, contingency, alternate, final reserve, and extra fuel, so the endurance and reserve check cannot be demonstrated.
Candidates compress the fuel plan into one number to save time, which makes it impossible to show that the aircraft lands with at least the required final reserve, and hides an inadequate alternate allowance.
What to do instead
Lay out the fuel plan as a vertical sum: taxi out, trip, contingency, alternate, final reserve, then any extra or tankering. Convert each leg to time using the planned power setting and check the total against usable capacity. Verify that fuel on arrival at the destination still covers alternate plus final reserve before you accept the plan.
Filing a flight plan or navigation log where the true airspeed, wind, and heading triangle is solved once and then reused for legs with different winds, or where magnetic variation and deviation are applied in the wrong order.
The triangle solution is laborious, so candidates compute it for the first leg and carry the heading forward, and the variation/deviation signs are easy to invert when converting between true, magnetic, and compass headings.
What to do instead
Solve the wind triangle for each leg with its own forecast wind, and write the conversion chain explicitly as true heading, then apply variation to get magnetic, then deviation to get compass. Check the sign of each correction against the rule that east variation is subtracted when going from true to magnetic, and verify the final compass heading against the planned track.
Quoting aircraft performance figures or mass limits from memory or from a similar type rather than from the specific aircraft's flight manual and mass and balance schedule in the documents carried.
Type training and sample questions build a mental 'typical' set of numbers, and candidates answer from that impression without opening the actual document, which is exactly the habit the exam is testing against.
What to do instead
For every numerical answer, cite the document and section you used: AFM limitation, mass and balance schedule, or performance supplement. If the question supplies figures, use only those; if it does not, state the assumption you are making and flag that the answer depends on the specific aircraft's approved data.
Confusing the documents that must be carried and current (certificate of airworthiness, certificate of registration, mass and balance report, flight manual, insurance, radio licence) with those that are merely recommended, and missing validity dates on the ones that expire.
The list is long and jurisdiction-dependent, and candidates learn it as a single block without the renewal or validity condition attached to each item, so they miss a lapsed item in a scenario question.
What to do instead
Build a two-column checklist: document, and validity or renewal condition (for example the mass and balance report being revised after a weighing or equipment change). Work through the scenario against that checklist and name the specific expired or missing item rather than answering 'documents incomplete'.