031 Mass and Balance topic guide
Operating Masses and Traffic Load
Every aircraft mass on a load sheet sits on one ladder. Basic empty mass is the aircraft itself, structure, engines and fixed equipment, with no crew, fuel or payload aboard. Add the crew, their baggage, catering and any removable operational equipment to reach dry operating mass, which still excludes useable fuel and traffic load. Add traffic load, the revenue passengers, baggage, cargo and mail, and the result is zero fuel mass. Add take-off fuel for take-off mass, and subtract whatever fuel is burned to reach the mass at any later point, landing included.
The exam leans on one question built from this ladder: which take-off mass is actually allowed. Three independent limits exist side by side: the maximum structural or performance-limited take-off mass, the maximum zero fuel mass plus the planned take-off fuel, and the maximum landing mass plus the planned trip fuel. The allowed take-off mass is whichever of the three is lowest, never an average, and never an assumption that one limit will dominate every flight.
The mass ladder in numbers
A short example fixes the sequence: basic empty mass 39500 kg, plus crew, catering and removable equipment of 1500 kg, gives a dry operating mass of 41000 kg. Add a traffic load of 9000 kg for a zero fuel mass of 50000 kg. Add 8000 kg of take-off fuel for a take-off mass of 58000 kg. Burn 6000 kg of trip fuel and the mass at landing is 58000 minus 6000, or 52000 kg.
- Basic empty mass: the aircraft with fixed equipment only
- Dry operating mass: basic empty mass plus crew, crew baggage, catering and removable equipment
- Zero fuel mass: dry operating mass plus traffic load
- Take-off mass: zero fuel mass plus take-off fuel
- Mass at any later point: take-off mass minus the fuel burned so far
Finding the lowest of three allowed take-off masses
The structural or performance-limited figure comes straight from the aircraft's certification or from the runway and obstacle performance calculation for the day, and it needs no further arithmetic. The other two limits work backwards from a mass that must never be exceeded at a later point in the flight: the maximum zero fuel mass plus the planned take-off fuel gives the highest take-off mass that still leaves the zero fuel mass within limits once that fuel is loaded, and the maximum landing mass plus the planned trip fuel gives the highest take-off mass that still leaves the landing mass within limits once that fuel is burned.
Calculate all three, every time, and take the lowest. Stopping after the first or most obviously quoted figure is the single most common way this question loses marks, because the limiting constraint is frequently the landing-mass or zero-fuel-mass calculation, not the structural figure the stem states directly.
Worked example
Worked example: the lowest of three allowed take-off masses
Not quite. The correct answer is C.
Correct answer: C
- A. This is only the structural limit. It is a valid ceiling on its own, but the other two limits have not been checked, and one of them is lower.
- B. This is the zero-fuel-mass-based limit (60000 + 9000), which is higher than the structural limit and is not the lowest of the three.
- C. Correct: the landing-mass-based limit is 56000 + 7000 = 63000 kg, which is lower than both the 68000 kg structural limit and the 69000 kg zero-fuel-mass-based limit.
- D. This is the maximum landing mass on its own, with the planned trip fuel never added back. The take-off mass must be high enough to still burn that fuel and land at or under 56000 kg.
Step by step
- List the structural limit directly: 68000 kg.
- Calculate the zero-fuel-mass-based limit: 60000 kg + 9000 kg take-off fuel = 69000 kg.
- Calculate the landing-mass-based limit: 56000 kg + 7000 kg trip fuel = 63000 kg.
- Take the lowest of the three (68000, 69000, 63000): 63000 kg is the maximum allowed take-off mass.
- Sanity check: at a take-off mass of 63000 kg, the zero fuel mass is 63000 - 9000 = 54000 kg, comfortably under the 60000 kg limit, and the landing mass is 63000 - 7000 = 56000 kg, exactly at its limit, confirming the landing mass is the true constraint.
Common mistakes
Stopping at the structural take-off mass without checking the other two limits
The structural figure is often the number stated most directly in the stem, which makes it tempting to treat as the answer, but the true limiting figure is frequently the lower zero-fuel-mass-based or landing-mass-based calculation.
Confusing dry operating mass with zero fuel mass
Dry operating mass excludes traffic load. Forgetting to add it before comparing against a zero-fuel-mass limit understates the mass the aircraft will actually be carrying at brakes release.
Using the maximum landing mass itself as if it were an allowed take-off mass
The landing-mass-based take-off limit must include the planned trip fuel that will be burned before touchdown. Quoting the landing mass alone ignores that fuel entirely and understates how much the aircraft may weigh at take-off.
Related topic guides
Practise Mass and Balance the way the exam asks it.
SkyStudy turns Operating Masses and Traffic Load and every other Mass and Balance topic into exam-style practice questions with explanations, spaced repetition, and timed mock exams. Free to start.
Important information
This page is general educational information for student pilots and may be out of date.
Aviation rules, training requirements, costs, medical standards, and exam details change over time and vary by country, authority, and training organisation, so details here may no longer be current or may differ in your case.
Always confirm the current details with your approved training organisation (ATO) and national aviation authority before relying on them.
SkyStudy is an independent study aid, is not affiliated with EASA or any aviation authority, and does not guarantee any exam or licence outcome.
Last reviewed July 2026