ATPL Performance (EASA) common mistakes
ATPL Performance · Understand the traps and how to avoid them.
Treating the published TORA as the distance available for the ground roll and rotating at the threshold, instead of subtracting the line-up allowance and applying the correct screen height at the end of TODA.
Candidates memorise 'TORA = take-off run available' and then use it as the only number on the chart. They forget that TODA includes the clearway and that the aeroplane must reach 35 ft (or the AFM-specified screen height) by the end of TODA, and they forget the line-up distance that eats into the run.
What to do instead
Before touching the chart, write down all four declared distances for the runway and note which one the chart is referenced to. Then apply the operator/AFM policy for line-up allowance and screen height explicitly. Practise converting a TODA-limited chart into an actual ground-roll limit by subtracting the airborne segment.
Using the wrong weight for the take-off calculation - either the actual take-off weight instead of the regulated take-off weight, or forgetting to add taxi fuel burn-off and trip fuel when computing the landing weight at destination.
Candidates conflate 'weight at the gate' with 'weight at brake release' and 'weight at touchdown'. Performance charts are weight-sensitive in a non-linear way, so a few hundred kilograms of unaccounted fuel can shift the answer outside the tolerance band.
What to do instead
Build a small weight ladder for every question: ramp weight, minus taxi fuel = take-off weight; take-off weight minus trip fuel = landing weight. Do this before reading the chart, and write each figure on the working so the examiner can see the logic.
Interpolating take-off and landing charts linearly between two weight or temperature lines when the chart's grid is non-linear, or rounding the answer to the nearest whole grid line instead of interpolating conservatively.
Charts are drawn with non-uniform spacing and curved correction lines; candidates treat them like a simple graph and take the midpoint. They also round in whichever direction makes the number look tidy.
What to do instead
Identify the chart's grid spacing and whether the parameter lines are straight or curved before interpolating. Always interpolate and then round in the safe direction (longer distance, lower weight, higher temperature). State the rounding direction in the answer.
Applying a single correction for wind, slope, temperature and pressure altitude in the wrong order, or applying a percentage correction to the already-corrected distance instead of to the correct base value.
Take-off charts typically give a base distance for ISA, zero wind, level runway, then require multiplicative or additive corrections. Candidates apply them in the order printed rather than the order the chart intends, or they compound percentages on the wrong base.
What to do instead
Write the correction sequence as a chain before calculating: base distance → pressure altitude/temperature → slope → wind → surface/contamination → obstacle. Check whether each correction is additive (metres) or multiplicative (per cent) and apply it to the value the chart specifies.
Forgetting that V1, VR and V2 are limited by more than one factor and quoting the chart value without checking VMCG, VMCA, tyre speed, brake energy and climb-gradient limits.
Candidates find a V1 on the chart and stop. They do not cross-check that the resulting V1 gives a workable balanced field, that VR is at least 1.05 times VMCA, or that V2 meets the 1.2 VS (or 1.13 VS for some configurations) requirement and the second-segment gradient.
What to do instead
For every V-speed question, list the limiting cases: VMCG, VMCA, minimum control speed in the air, tyre limiting speed, brake energy, and the second-segment climb gradient. State which limit is active and how it constrains the chosen value.
Using the take-off climb gradient for the second segment when the question is about the en-route or final take-off segment, or mixing up gross and net gradients.
The four take-off segments have different configurations, speeds and required gradients (positive, 2.4%, 1.2%, 1.2% for twins; higher for quads). Candidates learn one number and reuse it. They also forget that net gradient is gross minus 0.8% (twins) or 0.9% (quads) for the second segment and 0.5%/0.9% elsewhere.
What to do instead
Build a one-page table of segment, configuration, speed, required gross gradient and net deduction for the relevant aircraft class. Answer climb questions only after identifying the segment number and whether the question asks gross or net.
Calculating the obstacle-limited climb gradient without subtracting the net-to-gross margin, or comparing the achieved gradient to the obstacle slope without converting units (per cent vs degrees vs ft/NM).
Obstacle clearance questions mix gradients expressed as percentages, degrees and feet per nautical mile. Candidates compute a gradient in per cent and compare it directly to an obstacle height in feet without converting the horizontal distance.
What to do instead
Convert everything to one unit (feet per nautical mile is usually easiest) before comparing. Use the identity: gradient % = tan(angle) × 100, and 1% ≈ 60.8 ft/NM. Always apply the net-to-gross deduction when the requirement is stated as a net gradient.
Ignoring the effect of the tropopause and temperature deviations from ISA when computing true airspeed, Mach number and specific range in the cruise.
Candidates use the ISA temperature at the flight level without checking whether the actual temperature is above or below ISA, and they forget that above the tropopause the temperature is constant so TAS for a given Mach increases with altitude while the speed of sound does not change.
What to do instead
For every cruise question, state the ISA deviation first, then compute TAS and Mach from the correct temperature. Above the tropopause, hold temperature constant and note that TAS rises with altitude at constant Mach. Check whether the question wants TAS, Mach or ground speed.
Computing the landing distance without the 1.67 factor (or the applicable operator factor) and without the dispatch requirement that the destination and alternate landing distances are achievable at the expected landing weight.
Candidates quote the actual landing distance from the chart as the required landing distance. They also forget that the pre-flight planning requirement uses the expected landing weight at destination, not the take-off weight, and that a separate in-flight requirement applies.
What to do instead
Distinguish three numbers: actual landing distance from the chart, required landing distance (actual × 1.67 for dry, or the applicable factor for wet/contaminated), and the dispatch limit. State which one the question asks for and show the multiplication explicitly.
Failing to identify the limiting runway or the limiting obstacle when the question gives several runways or obstacles, and answering with the first value computed rather than the governing one.
Multi-runway and multi-obstacle questions are designed so that the obvious runway is not the limiting one. Candidates compute one case, get a plausible number, and stop. They also forget to check the obstacle on the climb-out and the obstacle on the approach separately.
What to do instead
For multi-option questions, tabulate every runway/obstacle combination before choosing. Mark the governing case explicitly (highest required distance, steepest required gradient, lowest permitted weight) and only then read off the answer. Check both take-off and landing obstacles.