CPL Flight Planning common mistakes
CPL Flight Planning · Understand the traps and how to avoid them.
Computing leg time by dividing distance by the filed TAS without applying the wind, or applying the wind triangle by simple arithmetic (adding/subtracting the wind component to TAS) instead of resolving it as a vector.
Candidates learn the TAS = distance/time formula first and treat wind as a minor correction; under exam pressure they reach for the simplest operation that produces a number, and the wind triangle is the step they are least fluent in.
What to do instead
Practise a fixed routine on every leg: lay off true course, apply wind with the vector (or the wind component formulas: headwind component = W × cos(angle), crosswind = W × sin(angle)), derive true heading and groundspeed, then time = distance/groundspeed. Always sanity-check that the groundspeed lies between TAS − wind speed and TAS + wind speed.
Converting between true, magnetic and compass directions in the wrong order or skipping variation/deviation, so a heading is out by 10–20 degrees and the track, time and fuel are all wrong downstream.
The sequence (true → magnetic → compass, or the reverse) is easy to memorise as a list but easy to apply backwards, and candidates often forget that deviation is aircraft-specific while variation is chart-specific.
What to do instead
Write the conversion chain on the working paper before starting: TRUE ± VAR = MAGNETIC ± DEV = COMPASS, with 'east is least' for westerly variation and the opposite for easterly. Do the conversion in both directions once as a self-test, and mark the result T/M/C so the examiner can see which value you used.
Totalling fuel as trip fuel plus a single reserve figure, omitting taxi, contingency, alternate, final reserve and additional/extra fuel, or applying the reserve to the wrong quantity.
Candidates conflate the different fuel components and their purposes, and in a timed exam they collapse the calculation into one subtraction rather than building up the fuel plan element by element.
What to do instead
Build the fuel plan in a fixed vertical list in the order: taxi, trip, contingency, alternate, final reserve, additional/extra, then total. State units and the basis for each (for example final reserve as a time at holding consumption). Check that fuel on board minus fuel used never falls below final reserve at any point.
Using the wrong mass or the wrong chart conditions in performance work - for example reading take-off distance for the actual weight when the chart is for a different flap setting, pressure altitude or temperature, or forgetting to apply the factor for runway slope, surface or wind.
Performance charts have several entry axes and correction grids; candidates pick the first chart that looks right and interpolate on the two most obvious axes, ignoring the header conditions and the correction notes below the graph.
What to do instead
Before reading any chart, read the title and conditions line aloud in your head: configuration, pressure altitude, temperature, wind, slope, surface. Enter the chart with the correct axes, interpolate, then apply every listed correction in the order printed. Finish by asking whether the answer is plausible for the aircraft type.
Computing weight and balance with the wrong datum reference, mixing moment units, or checking only the total weight against the limit without checking the centre of gravity position against the forward and aft limits.
Candidates focus on the arithmetic of moments and treat the CG envelope as an afterthought, and unit confusion (kg·m versus lb·in, index units versus moments) is common when the load sheet uses indices.
What to do instead
Set out a table with columns for mass, arm, moment and index, keep units consistent throughout, and state the datum at the top. After summing, plot or compare the CG against both the forward and aft limits for the actual mass, and repeat for zero fuel mass as well as take-off mass.
Filing a flight plan with a route, level, speed or time that does not match the cleared or planned profile - for example a cruise level inconsistent with the semi-circular rule for the track, or an elapsed time that does not reconcile with the sum of the leg times.
Candidates treat the flight plan form as a summary to be filled in from memory rather than a document that must be internally consistent, and they do not cross-check the level against the magnetic track.
What to do instead
Complete the form in a fixed order (aircraft, route, level, speed, times) and then run a consistency check: track versus level under the semi-circular rule, elapsed time versus the sum of leg times plus taxi, endurance versus fuel on board. Reconcile any difference before submitting.
Misreading a NOTAM or chart annotation - treating a temporary runway shortening, a closed taxiway, an unserviceable navaid or a changed frequency as if it did not affect the plan, or missing the validity period.
NOTAMs and chart amendments are dense text with abbreviations, and candidates skim for the item they expect rather than reading the whole entry including the validity window and the affected segment.
What to do instead
Read each NOTAM against a checklist: what, where, when (from/to, and whether it is active for the planned time), and what it changes in your plan. Note the effect explicitly in the plan (for example reduced declared distance, alternate navaid). Check chart amendment dates against the plan date.
Selecting an alternate or diversion aerodrome without checking that it is actually usable: weather above the required minima, runway length and surface suitable for the mass, fuel available, and within the fuel range at the planned level.
Candidates pick the nearest aerodrome by distance and assume it will do, forgetting that the alternate must satisfy weather, performance and fuel criteria simultaneously.
What to do instead
Test each candidate alternate against four gates in order: forecast weather versus planning minima, runway and performance at landing mass, fuel and time from the diversion point, and navaid/approach availability. Only then choose, and record the reason.
Planning the climb, cruise and descent as one average speed and one average fuel flow, so the time and fuel for the profile are systematically wrong, especially on short sectors.
A single cruise figure is simpler and candidates do not appreciate how much of a short sector is spent in climb and descent at very different speeds and flows.
What to do instead
Break every profile into climb, cruise and descent segments, each with its own distance, time and fuel from the aircraft tables, and sum them. On sectors under about 200 nm, check whether the aircraft even reaches the planned cruise level before top of descent.
Copying intermediate values incorrectly between steps - transposing digits, carrying a rounded figure forward into the next calculation, or losing a unit conversion - so the final answer is internally consistent but wrong.
Multi-step calculations under time pressure encourage mental arithmetic and rounding at every stage, and there is no written audit trail to catch the error.
What to do instead
Write every step with its units, keep full precision in intermediate values and round only the final answer, and carry out a reverse check (recompute time from distance and groundspeed, or fuel from flow and time). If two routes to the answer disagree, stop and find the discrepancy.