2.4 Weight, Balance & Cabin Loading
Key Takeaways
- Centre of gravity is the point through which the total weight of the aircraft acts, and it must remain between the forward and aft limits published for the aircraft at all times in flight.
- An aft centre of gravity reduces stability and can make recovery from a stall difficult, while a forward centre of gravity increases stability but raises stall speed and control forces.
- The loadsheet reflects the passenger distribution the flight crew have planned for, so cabin crew must not redistribute passengers between zones after the doors are closed without flight deck approval.
- Standard passenger and baggage mass values are used for planning; where actual seating differs materially from the loadsheet the flight crew must be told before departure.
- Overhead bins, closets and galley carriers have placarded maximum loads, and exceeding them is both a structural and a balance problem.
The cabin is part of the load
An airliner is loaded in three places: the cargo compartments, the fuel tanks, and the passenger cabin. Of the three, the cabin is the only one loaded by people who move around after loading is complete. That is why weight and balance is on the cabin crew knowledge syllabus.
The vocabulary
| Term | Meaning |
|---|---|
| Basic empty weight | Weight of the airframe, engines, fixed equipment, unusable fuel and operating fluids |
| Dry operating weight (DOW) | Basic empty weight plus crew, catering, cabin equipment and removable service items — everything except traffic load and usable fuel |
| Traffic load / payload | Passengers, their baggage, cargo and mail |
| Zero fuel weight (ZFW) | Dry operating weight plus traffic load. Certificated maximum zero fuel weight protects the wing structure, because fuel in the wings relieves bending loads |
| Take-off weight | Zero fuel weight plus take-off fuel; must not exceed maximum take-off weight or the performance-limited weight for the runway and conditions |
| Landing weight | Take-off weight minus trip fuel; must not exceed maximum landing weight |
| Centre of gravity (CG) | The point through which the total weight acts; must be within the forward and aft limits |
| Loadsheet | The document showing the calculated weights, CG and trim setting for the flight, signed by the pilot-in-command |
Why the centre of gravity matters
The aeroplane is balanced about its CG rather like a seesaw. The tailplane provides a small balancing force, and the elevator trim is set for take-off on the basis of the calculated CG position.
| CG position | Effect |
|---|---|
| Too far forward | Increased stability but heavier control forces, higher stall speed, longer take-off run and possible inability to rotate |
| Within limits | Certificated handling, expected performance and correct trim setting |
| Too far aft | Reduced stability, lighter and more sensitive controls, and a stall from which recovery may be difficult or impossible |
An out-of-limits CG is not a comfort issue. It changes whether the aeroplane can be flown at all.
Standard masses and why they are only a plan
For flight planning, operators use standard mass values for adult male, adult female, child and infant passengers, plus standard values for checked and cabin baggage, all approved by the Authority. Standard values are statistically safe across a full cabin but can be wrong for a particular flight — a charter carrying a sports team, a pilgrimage flight with heavy hand baggage, or a light load concentrated in one part of the cabin.
The relevant duty for cabin crew is to report, before departure, when the reality in the cabin differs materially from the plan:
- Large blocks of empty seats concentrated at the front or the rear;
- A group who have seated themselves together in one zone;
- Unusually heavy cabin baggage, equipment cases or musical instruments;
- Additional crew, engineers or company staff carried in the cabin who may not be on the loadsheet;
- A stretcher case, bulky medical equipment or a service animal.
Do not move passengers after the loadsheet is final
This is the single most examinable cabin crew weight-and-balance rule. Once the loadsheet is issued and the trim is set, the distribution of people in the cabin is part of the aircraft's certificated loading.
Rules to apply:
- Before doors close, seat changes within the cabin are normally managed by the operator's procedures, but any significant shift between zones must be reported so that the loadsheet can be recalculated.
- After the loadsheet is final and before take-off, do not authorise passengers to move between cabin zones without flight deck approval. On a lightly loaded regional aircraft, a dozen passengers relocating aft can move the CG appreciably.
- In flight, on a lightly loaded small aeroplane, keep the seating broadly as planned and consult the flight deck before any large redistribution.
- Never move a passenger into an exit row to solve a seating problem without applying the exit-seating criteria; the exit-row rules are a separate legal requirement and are covered in the aircraft exits chapter.
Cabin stowage limits
Every stowage in the cabin has a placarded maximum load, and the placard is the authority:
- Overhead stowage bins carry a maximum weight marked on or near the bin. Loading beyond it risks the bin latch failing in turbulence or on a heavy landing, dropping the contents on the occupants below.
- Closets and wardrobes have a maximum load and often a maximum number of items.
- Galley carriers, carts and containers must be latched and braked. An unbraked cart is both a loading problem and a lethal projectile.
- Under-seat stowage is limited to items that fit fully within the marked area and do not obstruct the row's escape path.
- Bulkhead and floor stowage is not permitted unless a certified restraint is fitted.
A worked scenario
A Dash 8 Q400 with 78 seats is dispatched with 30 passengers, and the loadsheet is calculated on the basis that they are seated across the whole cabin. After boarding, most passengers move to the rear rows to be near the airstair, leaving the forward cabin empty.
On a large jet this would be a minor effect. On a 78-seat turboprop with a light load it can move the CG towards or beyond the aft limit. The correct action is to stop the redistribution, reseat passengers as planned, and tell the flight deck what happened. If the flight crew decide a recalculation is needed, that is their call — but they cannot make it without the report.
Cabin crew do not calculate loadsheets. Their job in weight and balance is to keep the cabin looking like the loadsheet says it does, and to report immediately when it does not.
Why must cabin crew avoid authorising passengers to move between cabin zones after the loadsheet has been finalised?
What is the principal handling risk if the centre of gravity is beyond the aft limit?
Which weight limit exists principally to protect the wing structure from bending loads?
A cabin crew member finds that a passenger has stowed a heavy equipment case in an overhead bin that is already full. What is the governing consideration?