ATPL Flight Planning common mistakes
ATPL Flight Planning · Understand the traps and how to avoid them.
Computing trip fuel from the planned true airspeed and still-air distance while ignoring the wind component given for each leg, then carrying that error through to total fuel and endurance.
Candidates treat the cruise TAS as the ground speed because it is the most prominent number in the flight plan, and headwind/tailwind columns are easy to skip when time is short.
What to do instead
For every leg, write the wind component and compute ground speed explicitly (GS = TAS +/- headwind/tailwind, or resolve the wind triangle when drift is given). Recompute leg time as distance divided by ground speed and only then sum trip fuel; cross-check that the sum of leg times equals total endurance minus reserves.
Confusing the reserve fuel types and applying the wrong one: using the 30-minute holding reserve where a contingency percentage is required, or omitting the alternate fuel when an alternate is nominated.
The regulation lists several fuel components in similar wording, and candidates memorise one figure without linking it to the specific operational case (IFR commercial, VFR, alternate required or not).
What to do instead
Build a checklist of fuel components in fixed order: taxi, trip, contingency, alternate, final reserve, extra. For each, state the trigger condition and the calculation basis (percentage of trip fuel, time at holding consumption, or computed from destination to alternate). Apply the checklist to every practice scenario until the triggers are automatic.
Reading the wrong line or column in the fuel consumption or climb/descent tables, for example using cruise figures for the climb segment or interpolating between the wrong weight rows.
Performance tables are dense, weights may be in thousands of units, and candidates rush to the nearest familiar number instead of locating the exact entry conditions.
What to do instead
Before entering any table, note the entry conditions (pressure altitude, temperature, weight, configuration) on paper. Interpolate only between the two bracketing rows and show the interpolation arithmetic. Verify units (kg vs lb, thousands vs units) at the top of each column before using the value.
Mixing units or datum conventions: treating litres and kilograms interchangeably, using US gallons with imperial consumption figures, or combining a mass in pounds with a fuel flow in kilograms per hour.
Fuel is quoted in different units across aircraft types and documentation, and density conversions are often assumed rather than stated.
What to do instead
Write the unit next to every number in the working. Convert to a single system (usually kilograms) at the start using the stated density or the given conversion factor, and carry the unit through each step so a mismatch becomes visible before the final answer is selected.
Ignoring the effect of a change in planned level or routing on fuel: recalculating distance but not the revised cruise consumption, or forgetting that a lower level increases trip fuel.
Candidates treat the route distance as the only variable and assume the fuel figure from the original plan still applies after an in-flight replan.
What to do instead
When a level or route changes, re-enter the cruise table for the new pressure altitude and temperature, recompute leg times with the new ground speeds, and rebuild trip fuel from scratch. Compare the new total against fuel remaining to confirm the plan is still valid.
Treating the maximum take-off mass, maximum landing mass and maximum zero-fuel mass as a single limit, and checking only one of them against the calculated masses.
The three limits appear together in the mass and balance data and candidates check whichever one they remember, usually take-off mass.
What to do instead
Compute take-off mass, trip fuel, landing mass and zero-fuel mass in sequence, then test each against its own limit. If any limit is exceeded, state which one and by how much, and adjust payload or fuel accordingly rather than assuming the plan is acceptable.
Misreading the operational flight plan or ATS flight plan fields, for example taking the estimated elapsed time from the wrong column or confusing the alternate aerodrome entry with the destination.
Flight plan forms use abbreviated field indicators and similar-looking time entries, and under exam pressure candidates scan for the first plausible number.
What to do instead
Learn the field indicators and column headings as a fixed map before attempting calculations. When extracting a value, state aloud or in writing which field it came from and what it represents, then use it. Practise extracting a full set of values from one plan without doing any arithmetic, to isolate reading errors from calculation errors.
Failing to apply the validity and currency requirements of the documentation carried, such as using an expired chart or an out-of-date weight and balance schedule in the planning.
Candidates focus on the numbers and treat document validity as background knowledge, so they do not check dates against the planned flight date.
What to do instead
Add a documentation check step to every planning exercise: list each document required, its validity period, and its expiry date relative to the flight date. Treat any expired item as a planning error and note the consequence, since exam questions often hinge on exactly this point.
Overlooking the operational requirements that attach to the route, such as the need for an alternate, extended diversion time considerations, or the fuel penalty for a destination with no suitable alternate.
Candidates plan the fuel for the nominal route and forget that the operational rules change the fuel requirement when weather, distance or aerodrome suitability triggers them.
What to do instead
Before computing fuel, run a short operational screen: forecast weather at destination and alternate, distance to the alternate, and any rule that applies to the route type. Write the resulting fuel requirement down first, then compute. This makes the rule drive the numbers rather than the reverse.
Presenting a final fuel figure without a sanity check against endurance, remaining fuel at destination, or the aircraft's maximum fuel capacity.
Once a number is calculated, candidates move to the next question without asking whether the result is physically plausible for the aircraft and route.
What to do instead
After each fuel calculation, perform two checks: fuel remaining at destination must be at least the required reserve, and total fuel must not exceed capacity. If either check fails, re-examine the working for a unit, table or wind error before selecting an answer.