Learning Objective:

To understand:

  1. Why every gram being loaded on the aircraft is weighed with scrutiny?
  2. Why do pilots sometimes dump fuel ?

In an aircraft, the centre of gravity (CG) is the point about which the aircraft would balance when it is suspend by that point. As the location of the centre of gravity affects the stability of the aircraft, it must fall within specified limits that are established by the aircraft manufacturer. Both lateral and longitudinal balance are important, but the primary concern is longitudinal balance; that is, the location of the CG along the longitudinal or lengthwise axis.

From “Manufacturing” to “Commissioning” and from “On the Ramp” to “Take-off” there are huge variations in the weight and balance of an aircraft. It varies significantly, so striking a correct balance with all loads on an aircraft is significantly important.

Prerequisites:

  • Weight of a male person – 88 kg (avg)
  • Weight of a female person – 70 kg (avg)
  • Weight of children (2-12) years – 35 kg (avg)
  • Weight of cabin crew – 75 kg (including 3kg of crew baggage) (avg)
  • Weight of fuel in aircraft can be approximated as approx 12000 kgs for 4000 km by an narrow body aircraft (A-320).
  • Payload – Passengers, Cargo, Mail, Baggage. (mainly)

Let’s take these weights one by one.

  1. Manufacturer’s Empty Weight (MEW): It is the weight of the aircraft “as built” and includes the weight of the structure, power plant (engines), furnishings, installations, systems and other equipment that are considered an integral part of an aircraft.
  2. Zero Fuel Weight (ZFW): This is the total weight of the airplane and all its contents including unusable fuel (unusable fuel is the fuel which is required to maintain the structural stability of the aircraft, especially wings), but excluding the total weight of the usable fuel on board (usable fuel is the fuel necessary for the flight). Note: As a flight progresses and fuel is consumed, the total weight of the airplane reduces, but the ZFW remains constant.
  3. Operational Empty Weight (OEM) or Dry Operating Weight (DOW): It is the basic weight of an aircraft including the crew, all fluids necessary for operation, (such as engine oil, engine coolant, water, unusable fuel) all operator items and equipment required for flight but excluding usable fuel and the payload.
  4. Maximum Zero Fuel Weight (MZFW): Maximum zero fuel weight (MZFW) is the maximum weight allowed before usable fuel and other specified usable agents (engine injection fluid, and other consumable propulsion agents) are loaded. OR (OEM / DOW + Payload = MZFW)
  5. Maximum Taxi Weight (MTW) or Maximum Ramp Weight (MRW): It is the maximum permitted weight of the aircraft at which it may be moved on the ground either with its own engine or towed by a tractor. It can also be defined as maximum weight for ground maneuvering including the weight of run-up and taxi fuel. (MZFE + Ramp Fuel = MRW)
  6. Maximum Take-Off Weight (MTOW): It is the maximum permitted weight at the start of the take-off. While determining this limit, the manufacturer takes into consideration the strength of the material used for the manufacturing of the aircraft and standard performance variables such as runway temperature, altitude, atmospheric pressure, wind components, flaps, etc. (MZFW + Take-Off Fuel = MTOW)
  7. Regulated Take-Off Weight (RTOW): As told in the above definition depending on different factors (e.g. flap setting, altitude, air temperature, length of runway), RTOW or maximum permissible takeoff weight varies for each takeoff. It can never be higher than MTOW. 
  8. All Up Weight (AUP): DOW + Payload + Fuel.
  9. Maximum Landing Weight (MLW): When aircraft touches the ground it puts force of the runway as well as on the tyres and under carriage, so to ensure structural safety of the aircraft MLW is taken into consideration. Manufactures have calculate this force to be approximately “9” times the weight of the aircraft. Thus when the aircraft has to make an emergency landing or when the weight of the aircraft before landing exceeds the MLW defined by the manufacturer the pilots dump fuel to reduce the weight of the aircraft. (MTOW – Trip Fuel = MLW)

To sum up and to get a more clear picture, have a look on the image below:

We hope that now you have got an understanding of why each and every baggage is weighed before it is loaded on the aircraft which is not the case when you travel by train. So next time you try to negotiate kgs with the airline staff remember its not that the staff is being insensitive and but you are trying to compromise on your safety.

To enhance your understanding have a look at the problem below:

  1. Assume:
  • Avg Passenger Weight – 77 kgs
  • Avg Baggage Weight – 20 kgs

2. Given Data:

  • DOW – 46000 kgs
  • TOF – 15000 kgs (Take-Off Fuel)
  • ZFW – 62500 kgs
  • MTOW – 77000 kgs
  • LW – 66000 kgs (Landing Weight)
  • TF – 10000 kgs (Trip Fuel)

Q. Find the maximum allowable load (payload) and the underload of the aircraft?

Sol. First we will try to find Operating Weight (OW is not a standard weight defined but is required for the calculations performed) . So, according to the problem given we can find operating weight using the following three methods:

a. DOW+TOF = OW(1) = 46000+15000 = 61000 kgs

b. ZFW+TOF = OW(2) = 62500+15000 = 77500 kgs

c. LW + TF = OW(3) = 66000 + 10000 = 76000 kgs

Now in order to find the maximum allowable payload we will choose the minimum OW and proceed further, which is OW(1).

Now question says to find the Allowable Load (payload). So, MTOW – OW(1) = Payload (1) = 77000 – 61000 = 16000 kgs.

Where Payload (1) is the maximum allowable payload on the aircraft.

If we consider a scenario that the flight has 120 passengers, 600 kgs of Cargo and 600 kgs of Mail. Then,

  • Passenger Weight = 120 * 77 = 9240 kgs
  • Baggage Weight = 20 * 120 = 2400 kgs
  • Cargo Weight = 600 kgs
  • Mail Weight = 600 kgs

All of the above cumulates to the Payload (2) = 12840 kgs

Now, Paylaod (1) – Payload (2) = 16000- 12840 kgs = 3160 kgs (Under load)

This means the flight still can accommodate 3160 kgs more.

Amazing right? Comment in the section down below and let us know what other topics you would like to read about.

Go where you feel the most alive!!

One thought on “All kinds of “Weights” for an Aircraft: Basics of Load and Trim

  1. Very informative… Seeking suggestions from the readers about the topics they would love to read in future are welcome gesture….But, do not depend too much on them as they may forget the issue…

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