ATPL · illustrated course

ATPL mass and balance course: 11 illustrated chapters

The ATPL mass and balance course follows the syllabus in 11 chapters: 83 key points explained in a few paragraphs, often with a diagram, what to remember and, for many, the classic exam trap. The first chapter, « Aeroplane and Load Masses », can be read in full on this page.

Read chapter 1 The 619 questions of this subject

Each chapter explains, point by point, what the questions of the bank ask, with a « Remember » box and often the classic exam trap. The first chapter is free, below and in the app; the next ones are for ATPL subscribers.

1.Aeroplane and Load Masses
Free
Empty mass, basic mass, traffic load, fuels and operating masses: the vocabulary of every mass and balance sheet.
9 key points · 66 questions of the bank
2.Maximum masses and limitations
Subscribers
Maximum structural and performance masses, the physical reasons for each limit, load factor and the effects of overloading.
9 key points · 67 questions of the bank
3.Allowable take-off mass and available payload
Subscribers
The four calculations of the effective limitation, the available payload, the underload, the maximum fuel and the diversion cases.
8 key points · 60 questions of the bank
4.Centre of gravity, arms and moments
Subscribers
Definition of the CG, the datum, the sign of arms, moments, the balance of a lever and the calculation of the CG position.
7 key points · 53 questions of the bank
5.Weighing the aircraft
Subscribers
When and how to weigh an aircraft, individual and fleet masses, accuracy, and calculating the empty mass and its centre of gravity.
6 key points · 28 questions of the bank
6.Centre of gravity as a percentage of mean aerodynamic chord
Subscribers
Definition of the MAC and the LEMAC, converting arm ↔ % MAC, and exercises on CG shifts expressed in % MAC.
6 key points · 31 questions of the bank
7.Moving, adding or removing a mass
Subscribers
Moment equations for a cargo transfer, an addition or a removal, and the direct formulas used in the exam.
8 key points · 38 questions of the bank
8.Effects of Centre of Gravity Position on Flight
Subscribers
What sets the forward and aft limits, stability and neutral point, effects of a forward or aft CG, landing gear, flaps and fuel.
7 key points · 50 questions of the bank
9.Standard masses and fuel
Subscribers
Actual or standard masses of crew, passengers and baggage (Air OPS), choice of system, density and conversions.
7 key points · 37 questions of the bank
10.Floor limits, unit load devices and load securing
Subscribers
Maximum loads per compartment, running load and area load, containers and pallets, hold table and load securing.
8 key points · 31 questions of the bank
11.Mass and balance documentation, index and load sheets
Subscribers
Regulatory content of the mass and balance document, index, load sheet and trim sheet of the twin-jet, light aircraft manifest, CG envelopes and last-minute changes.
8 key points · 60 questions of the bank

Chapter 1: Aeroplane and Load Masses

Empty mass, basic mass, traffic load, fuels and operating masses: the vocabulary of every mass and balance sheet.

Why a mass and balance sheet

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The two checks of the mass and balance sheet: mass and balance

Before every flight, the pilot-in-command must make sure that the mass of the aeroplane and the distribution of the load stay within the limits, on the ground and in flight.

Two families of limits, defined by the manufacturer and certified by the authority, are published in the "Limitations" section of the Aircraft Flight Manual (AFM):

the structural maximum masses, which protect the airframe and the landing gear;
the balance limits (position of the centre of gravity, CG), which ensure stability and handling.

Undetected overloading degrades structural margins, performance and handling alike (rotation at take-off in particular).

The Basic Empty Mass (BEM)

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What the Basic Empty Mass contains

The empty mass (basic empty mass, *Basic Empty Mass*, or equipped empty mass) is the mass of the aeroplane "as it leaves the factory", ready to receive its crew:

airframe, engines, systems and fixed equipment;
fluids contained in the systems (hydraulic, etc.);
unusable fuel;
engine oil.

It is obtained by weighing and entered, together with its centre of gravity, on the weighing report. The value to use is that of the latest version of the report, corrected for modifications made to the aeroplane since. It is included in the basic mass.

Remember

Empty mass = standard empty mass + specific equipment + system fluids + unusable fuel.

Exam trap

Unusable fuel is part of the empty mass, not of the fuel on the mass and balance sheet. Consumable fluids (drinking water, toilet chemicals) are not included: they go into the variable equipment.

The basic mass (DOM)

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Basic mass = empty mass + variable equipment

The basic mass, or dry operating mass (*Dry Operating Mass*, DOM), is the total mass of the aeroplane ready for a given type of operation, excluding usable fuel and traffic load.

DOM = empty mass + variable (or operational) equipment, that is, the items that change from flight to flight:

crew (pilots and cabin crew) with their baggage and documentation;
catering (meals, drinks, newspapers) and removable passenger service equipment;
drinking water and toilet chemicals;
specific safety and survival equipment, occasional on-board kit.

Determining the mass of these items and of the crew is the responsibility of the operator.

Exam trap

"Basic mass" means the DOM, not the Basic Empty Mass. Also do not confuse "dry operating mass" (DOM) with "operating mass" (DOM + take-off fuel).

Traffic load and zero fuel mass

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Building up the zero fuel mass

The traffic load is the total mass of passengers, baggage, cargo and mail, including any non-revenue load (empty containers, for example).

The zero fuel mass (*Zero Fuel Mass*, ZFM) is the mass of the loaded aeroplane, excluding usable fuel:

ZFM = DOM + traffic load;
ZFM = TOM − take-off fuel.

Conversely: traffic load = ZFM − DOM, and DOM = ZFM − traffic load. The two masses therefore differ by exactly the traffic load.

Remember

ZFM = DOM + traffic load. Only usable fuel is excluded.

Exam trap

If the question gives the total fuel "including x kg unusable", subtract only the usable fuel from the TOM to find the ZFM. Some questions state "basic mass + traffic load and unusable fuel": the unusable fuel is in fact already included in the basic mass. Choose "the traffic load" if it is offered on its own; otherwise "traffic load and unusable fuel" (never an option that adds the crew, already in the DOM).

The fuels on the mass and balance sheet

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Breakdown of the fuel on board

Fuel is broken down into portions that you must know how to add up:

trip fuel: from brake release to landing at the destination;
reserves: contingency fuel, alternate fuel, final reserve (30 min holding at 1,500 ft above the alternate for a turbine-engined aeroplane, 45 min of flight for a piston-engined aeroplane), additional and extra fuel;
take-off fuel (TOF) = trip fuel + reserves;
block fuel = TOF + start-up and taxi fuel.

The fuel remaining at landing equals TOF − trip fuel, that is, the unused reserves.

Remember

Block = taxi + TOF; TOF = trip + reserves; fuel at landing = TOF − trip.

Exam trap

Taxi fuel is used before brake release: it counts neither in the TOM nor in the operating mass.

Masses stacking up

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Stack of masses, from BEM to ramp mass

All the operational masses are deduced from one another:

TOM (actual take-off mass, at brake release) = DOM + take-off fuel + traffic load = ZFM + TOF;
ramp mass (at parking) = TOM + taxi fuel;
LM (landing mass) = TOM − trip fuel = DOM + traffic load + fuel at landing.

Read the diagram from bottom to top: each line corresponds to a mass on the mass and balance sheet.

Remember

LM = TOM − trip fuel; ramp mass = TOM + taxi fuel.

Useful load and operating mass

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Useful load and operating mass

Two groupings come up often:

the operating mass (OM) = DOM + take-off fuel (at brake release); this is the mass of the aeroplane ready to depart, without the traffic load;
the useful load = traffic load + usable fuel at take-off = TOM − DOM.

It follows that traffic load = TOM − OM. The difference between useful load and traffic load is therefore the usable fuel.

Exam trap

In "useful load", the crew is not counted: it is already included in the DOM. If the problem statement gives a separate crew mass when the DOM is known, do not subtract it a second time.

Worked exercises

Finding the DOM. TOM 66,700 kg, traffic load 14,200 kg, fuel 10,500 kg: DOM = 66,700 − 14,200 − 10,500 = 42,000 kg (the crew mass also given is a distractor: it is already included).

Finding the useful load. Empty mass 61,300 kg, operational items 2,300 kg, TOM 132,000 kg: DOM = 63,600 kg; useful load = 132,000 − 63,600 = 68,400 kg.

Finding the traffic load. DOM 5,210 kg, ZFM 6,230 kg: 6,230 − 5,210 = 1,020 kg (trip fuel and TOF are not needed here).

Finding the TOM. ZFM 4,770 kg, block fuel 1,960 kg including 20 kg of taxi fuel: TOM = 4,770 + 1,940 = 6,710 kg.

Remember

First identify the formula that links the unknown to the relevant data: many of the figures in a problem statement are not needed.

Summary of formulas

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Operational mass formulas

This table summarises the relationships to know by heart. They all follow from the stack of masses seen above.

Remember the two starting points: the DOM for large aeroplanes, and the empty mass (BEM) for light aeroplanes, whose mass and balance sheets often start directly from the empty mass.

The course goes on with chapter 2, « Maximum masses and limitations ». It is read in the Course tab of the app with a ATPL subscription, and each chapter ends with the questions of the bank about it. See pricing

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Contents

Chapter 1: Aeroplane and Load Masses

Why a mass and balance sheet

The Basic Empty Mass (BEM)

The basic mass (DOM)

Traffic load and zero fuel mass

The fuels on the mass and balance sheet

Masses stacking up

Useful load and operating mass

Worked exercises

Summary of formulas

How ForAllPilots trains you

The other ATPL courses