Load and Trim Sheet

The load and trim sheet is the document that proves, before each flight, that an aeroplane is loaded within its mass and centre of gravity (CG) limits. It can be a printed form completed by hand, a computer printout from the operator's load control system or a page in an electronic flight bag, but its content is the same. The load sheet part adds up masses; the trim sheet part finds the balance and, on most airliners, the stabiliser trim setting for take-off.

The document matters because every later number depends on it. The take-off speeds, the trim setting and the fuel figures in the flight management system all start from the masses and CG it gives. A load sheet error may not show itself until rotation, when a wrong CG or trim setting can cause a tail strike or a reluctant rotation, which is why crews run gross error checks on it (see centre of gravity).

Mass and balance documentation

EASA's term is mass and balance documentation. The rule, carried over from EU-OPS 1 Subpart J into the Air Operations Regulation, requires the operator to establish it before each flight, in a form that lets the commander confirm that the load and its distribution are within the limits of the aeroplane. The documentation must:

• give the name of the person who prepared it;
• be signed by the person who supervised the loading, confirming that the load was placed as documented;
• be accepted by the commander, normally by signature;
• be kept for at least 3 months after the flight, like the operational flight plan.

Loading itself must be supervised by qualified personnel and must match the data used for the calculation. The loading, mass and CG must comply with the Aeroplane Flight Manual limits, or the Operations Manual limits where these are more restrictive, in every phase of the operation.

The required content, as the exam texts list it, is:

The load manifest and the mass build-up

Load manifest is the FAA name, and the exam texts use "load sheet (load manifest)" for the same document. Under 14 CFR 121.665 a Part 121 certificate holder is responsible for a load manifest before each take-off, and 121.693 lists what it must show: the weight of the aircraft, fuel and oil, cargo and baggage, passengers and crew; the maximum allowable weight for the flight; the total weight computed under approved procedures; evidence that the aircraft is loaded within its CG limits; and the passengers' names unless kept elsewhere. The pilot in command carries a copy to the destination.

The load sheet builds the masses in a fixed order, each one tested against its own ceiling (see aircraft mass definitions and maximum structural and regulated masses):

1. Dry operating mass plus traffic load gives the zero fuel mass, which must not exceed the maximum zero fuel mass.
2. Zero fuel mass plus take-off fuel gives the take-off mass, which must not exceed the regulated take-off mass.
3. Take-off mass plus start and taxi fuel gives the ramp mass, limited by the maximum taxi mass.
4. Take-off mass minus trip fuel gives the landing mass, which must not exceed the regulated landing mass.

The allowed traffic load comes from whichever limit bites first. Take a light twin with a maximum take-off mass of 2,800 kg, a maximum landing mass of 2,650 kg and a maximum zero fuel mass of 2,500 kg, a dry operating mass of 1,600 kg, 400 kg of take-off fuel and 100 kg of trip fuel. The landing limit allows a take-off mass of 2,650 + 100 = 2,750 kg; the zero fuel limit allows 2,500 + 400 = 2,900 kg. The lowest is 2,750 kg, so the traffic load is 2,750 − 1,600 − 400 = 750 kg, not the 800 kg that the take-off limit alone would suggest.

Index units and the moment index

An airliner's moments are huge, and a column of seven- and eight-figure numbers invites mistakes. The load sheet therefore uses a loading index, which is a moment divided by a constant. Light aircraft handbooks do the same with a moment index, usually the moment divided by 1,000: a 170 lb passenger at 85 in has a moment of 14,450 lb-in and a moment index of 14.45. When an index is turned back into a CG, it must first be multiplied by its constant. A total moment index of 274.5 at 3,050 lb is 274,500 lb-in, so the CG is at 274,500 ÷ 3,050 = 90.0 in.

Airline trim sheets usually go one step further and measure the moment about a reference station rather than about the datum:

index = mass × (arm − reference arm) ÷ K + constant

The divisor K and the constant are chosen by the manufacturer or operator. Items forward of the reference station give negative index changes and items aft of it positive ones, and the constant keeps the totals positive. With a reference arm of 20 m and K = 1,000, an 80 kg passenger at 30 m adds 80 × 10 ÷ 1,000 = +0.8 index units, and the same passenger at 12 m subtracts 0.64. The constant is included once, in the dry operating index; each item then adds its own change. Because the relation is linear, indices add and subtract exactly like moments, but an index from one type or one operator's sheet means nothing on another.

View full schematic

Dry operating index

The dry operating index (DOI) is the index of the aeroplane at its dry operating mass, with the crew and their baggage, catering, removable service equipment, potable water and lavatory chemicals on board. It comes from the aeroplane's weighed empty mass and CG plus the operator's standard items (see aircraft weighing). Where a fleet of the same model and configuration uses an average dry operating mass and CG, one DOI serves every aircraft in it. A departure from the standard crew or catering (pantry) load, such as an additional crew member or a heavier galley load, changes both the mass and the index and is applied as a correction to the dry operating mass and the DOI.

Fuel index

Fuel is handled separately because its arm is not fixed. On a swept-wing aeroplane the wing tanks fill and empty in a set order and the fuel moves along the sweep as the quantity changes, so the arm of the fuel on board varies with the quantity. The trim sheet therefore reads the fuel index from a table of fuel mass against index, rather than multiplying by a single arm. The take-off fuel index is added to the zero fuel index to give the take-off index; the landing index follows from the fuel remaining.

The zero fuel CG is checked as well as the take-off CG, because the CG travels between the two as fuel is burned. If both are inside the envelope, the CG stays inside it throughout the flight, provided the tanks are used in the prescribed sequence (see fuel mass and fuel loading).

Completing the trim sheet

The trim sheet turns the load distribution into points on the CG envelope:

1. Start from the DOI.
2. For each hold and each cabin zone, move the index by the amount the sheet gives for the mass loaded there. Graphical sheets print a scale for each compartment, so the index is walked across the page line by line; computer sheets do the same arithmetic.
3. The result is the zero fuel index. Plotted against the zero fuel mass on the envelope it gives the zero fuel CG, usually read in %MAC.
4. Add the fuel index to get the take-off index, plot it against the take-off mass and read the take-off CG. On many types the sheet then gives the stabiliser trim setting for take-off.

Each point must lie inside the envelope or on its boundary. In the EASA exam the medium-range jet data sheet draws the envelope in %MAC with mass on the vertical scale, and both the zero fuel and the take-off points are tested.

The crew then carry the result into the aircraft. Airbus crews enter the zero fuel weight and zero fuel CG in the flight management system and set the trimmable horizontal stabiliser from the load sheet value; Boeing crews check the gross weight and cruise CG against the dispatch papers. Both pilots compare the load sheet figures with the performance data and the FMS, because studies of take-off performance data have found frequent entry errors, including wrong weights and wrong runways.

Last minute changes

A last minute change (LMC) is any change to the load after the load sheet has been completed: a late passenger, a no-show whose bag is offloaded, late freight or a change of fuel. The rule is simple: an acceptable LMC must be documented. The commander is told the corrected masses and indices, checks that the masses and both the zero fuel and take-off CG are still within limits, and keeps the authority to refuse the change. The Operations Manual states the largest change in passengers or hold load that may be handled as an LMC; a larger change needs new mass and balance documentation. Electronic loadsheet applications, such as the one in the Airbus EFB suite, include an LMC function.

A change of mass is also a change of balance. Twenty passengers moving from an aft zone to a forward zone leave the mass unchanged but shift the index, and a late bag in the aft hold does both. After any LMC the FMS entries and the take-off trim setting are checked against the corrected figures and updated where needed.

Regulatory basis (EU-OPS Subpart J)

The European mass and balance rules were long found in EU-OPS 1 Subpart J (Mass and Balance), and question banks still quote it by that name. Since the Air Operations Regulation replaced EU-OPS, the same requirements sit in the mass and balance section of Part-CAT, CAT.POL.MAB, of Regulation (EU) No 965/2012, with the details in its acceptable means of compliance. The content is largely unchanged: weighing, traffic load by actual or standard masses, fuel mass by actual or standard density, loading under supervision, and documentation before each flight.

In the United States, Part 121 carriers work under an approved weight and balance control programme described in FAA Advisory Circular 120-27F, which covers the passenger and bag weights used, periodic aircraft weighing and the load manifest. For light aircraft the pilot's own mass and balance calculation, using the aircraft's current weight and balance record, serves the same purpose as the airline load sheet.

Library articles are written for study and exam preparation. They do not replace your aircraft's approved documentation, your operator's procedures or the regulations themselves.