The take-off weight of any commercial aircraft (equipped to fly a given route) will consist of the aircraft empty weight, the operator’s items, payload (passengers, baggage, and any cargo) and the fuel load (including reserves).
The aircraft empty weight (or Manufacturer’s Weight Empty (MWE)*) may be considered as the weight of the aircraft as it leaves the production line.
The Manufacturer’s Weight Empty includes:
- Aircraft structure (wings, fuselage, tail surfaces, landing gear etc.),
- Powerplant (engines, fairings, nacelles etc.),
- Aircraft systems (tanks, electrical, hydraulics, avionics etc.) and,
- Fixed equipment & furnishings (galleys, lavatories etc.)
Manufacturers strive to reduce aircraft empty weight by employing lightweight materials and new & improved manufacturing techniques. Each new aircraft leaving the production line has a detailed weight and balance report and thanks to modern manufacturing processes, even large jets (of the same type), will have very consistent empty weights when leaving the production line.
For modern commercial jets, 45 to 50% of the total aircraft weight will be composed of the aircraft empty weight.
Aircraft re-weighing is a continuous airworthiness requirement, for example, under European regulations aircraft are re-weighed every four years or whenever there are changes which significantly impact the aircraft weight & balance (cabin upgrades, aircraft modifications, etc.).
Operators may often notice increases in the aircraft empty weight even though no physical changes have been made to aircraft. Excluding possible weighing tolerances, these increases may often be primarily attributed to accumulation of matter (mostly moisture, waste and to a lesser extent dirt and dust build-up in the aircraft).
Operator’s items include those items added by the operator for flight execution and service reasons. They typically include:
- Galley structure & equipment
- Catering & passenger service equipment
- Water for galleys & lavatories
- Passenger seats, jump seats, life vests
- Emergency/cabin safety equipment
- Cockpit & cabin crew
- Containers & pallets
- Aircraft documents, flyway/tool kits and manuals
Operators can consider several ways to control the weight of these items, for example, by removing unnecessary equipment (e.g. reviewing contents of flyaway kits), using lightweight materials, reducing, or eliminating packaging and adjusting passenger related service items (catering, food & beverages, and potable water) to actual passenger numbers and sector lengths.
Adding the operator’s items weight to the Manufacturer’s Weight Empty gives the Operational Weight Empty (OWE), it is the weight of an equipped aircraft but without any payload or fuel on board.
The payload weight includes passengers, their baggage and any cargo that is carried. As passengers are (usually) not weighed, their weight (including hand baggage) is estimated based on standard allowances which may vary between passenger type; male, female, child (& infant) but also type of flight (scheduled, charter), time of the year and geographical zone. Significant differences in actual passenger payload weight and those obtained by applying standard allowances may give discrepancies in on board fuel calculations, planned versus actual fuel comparisons and even flight profiles.
As passenger payloads are estimated, operators may wish to confirm more precise values by conducting passenger surveys which involve weighing a representative sample of passengers taking into account type of operation, route flown, in/outbound flights and possible seasonal effects. Procedures for establishing revised passenger (plus hand baggage) weight allowances may be defined in the corresponding regulations.
Unlike passengers, checked baggage (and any cargo) is usually weighed and hence this weight is known more accurately.
Adding the payload weight to the Operational Weight Empty (OWE) gives the Zero Fuel Weight (ZFW), it is the weight of an equipped aircraft with passengers plus their baggage and any cargo but without any fuel on board. We may attain the Maximum Zero Fuel Weight (MZFW) of the aircraft, which is a certified operational weight limit that should not be exceeded.
Fuel quantities are calculated in the flight plan and include the fuel load legally required to fly from departure to arrival and a reserve fuel amount to account for uncertainties in the flight (en-route reserve or contingency fuel) and unforeseen circumstances (diversions, holdings).
There can be other fuel elements which are specific for the type of operation, e.g. ETOPS flight, depressurization scenarios, engine-out escape routes, icing conditions etc.
At the planning stage, the more precise the information related to the actual flight conditions, the more precision in the fuel loads calculated for the flight. Improving flight plan accuracy (in particular for more accurate fuel quantities) is a subject which merits further discussion and will be dealt with in a future article.
Adding the fuel load to the Zero Fuel Weight (ZFW) gives the Take-off Weight (TOW), it is the weight of an equipped aircraft with passengers plus their baggage, any cargo and with a quantity of fuel including a reserve fuel required to fly a given route. We may attain the Maximum Take-off Weight (MTOW) of the aircraft, which is a certified operational weight limit that should not be exceeded.
Reducing aircraft weight and more precise estimates of weight items will lead to reduced fuel burn and more accurate fuel burn predictions. This becomes increasingly important for those aircraft operating at their operational limits on the most demanding routes where a reduction in aircraft weight may be directly translated into an improvement in payload.
Operators can adopt several practices related to aircraft weight such as tracking aircraft empty weight (MWE) and optimizing operator’s item weights by removing unnecessary items, adjusting weight of items dependent on passenger numbers, flight times etc. and switching to light weight items when possible and cost effective. Precision in payload weights (passenger, baggage & cargo) also helps in fuel predictions and improving consistency between planned and actual fuel and flight profile parameters.
(*) Note that terminologies related to weight definitions may differ between manufacturers as well as the items included in these weights.
Madan Virdee
Fuel & Flight Efficiency Expert at NAVBLUE
