October 28, 2017

Operating and performance limits of airplanes are determined at the design stage. All expectations are clarified in advance and the plane is designed within the conditions of the day, parallel to these expectations. This means that the limits of an aircraft is known before their production. This is quite usual for aviation because it is not desirable to make a design that will not be preferred by companies.

Without exception, every commercial passenger plane has two basic limits; maximum take-off weight (MTOW) and minimum operating weight (MOW).

If we go into these limits in detail, the maximum take-off weight is the highest total weight that the plane can take off, as the name implies. This amount includes all items such as fuel, passenger, luggage, cargo, hardware, food / beverage and clean / dirty water. If the aircraft is heavier than this weight, it cannot take off.

The minimum operating weight is the empty weight together with the equipment that must be possessed so that the aircraft can fly safely. This amount doesn’t include any aforementioned items, except essential technical fluids such as oil / hydraulic. It expresses the total weight of the minimum equipment required to fly the aircraft, including pilots and cabin crew. The plane can not be lightened more than this weight.

These two limits confine us to a range of maximum and minimum weight. We can make it a little clearer with sample numbers.

Let's say that the maximum take-off weight of our aircraft is 79000 kg and the minimum operating weight is 38000 kg.

For all our remaining needs, we have a total of 79000 kg - 38000 kg = 41000 kg.

When we assess our basic needs, which we rank first, on this figure one by one;

Passengers are undoubtedly the first and most important factor. Since there is no possibility to weigh all the passengers one by one before each flight, acceptance is made with avarage values. Although some passengers are heavier and some passengers lighter, making an assumption of an average of 80-85 kg per passenger is possible. Even if we ask why it is 80-85 kg, the average value according to the statistics comes out around this numbers.

Every traveler will have at least a small baggage. With the same approach it would be reasonable to accept an average of 20-25 kg total luggage. We can think of this as 20 kg of checked luggage and 5 kg of cabin bags.

How many passengers can we get? For example, the design limit of our plane is 200 passengers. If we wanted to operate our aircraft at the highest passenger capacity, then we had 200 passengers x 100 kg total passengers and baggage weight = 20000 kg. We have 21000 kg left.

Are we going to offer food and drink to the passengers? If we offer 1 bottle of water, 1 cup of tea or coffee, and a sandwich to each passenger, we will use about 200 kg more, based on 1 kg per passenger. We have about 20800 kg left.

If we need to carry extra cargo in addition to the same flight, we will have to allocate a certain amount of cargo. If we assume that we will receive 2,000 kg of cargo for our example, we will have about 18,800 kg left in the last case.

Cabin equipment is also important. Are we going to give passengers comfortable or comparatively lighter economic seats? Are they going to have a magazine to read, screens for watching movies, many of toilets to keep the queues from forming? If we accept that we have light seats, a small magazine, and no movie/music options, we will have to devote an average of 10 kg per passenger and 2 000 kg in total. So our remaining capacity was reduced to 16800 kg.

Whether or not we serve food, it is certain that toilet will be needed. It is also necessary to reserve a capacity for clean water (and waste water) for use in toilets. Let's also assume that a median acceptance is required for toilet needs of a total of 200 kg per 1 kg per passenger, including flushing and hand washing. In the last case, we have 16600 kg capacity left.

We are obliged to buy fuel, but it is now clear how much fuel we can get. We can get 16600 kg fuel at most. When the fuel tank has a capacity of 35000 kg, we have no chance to fill it full. Which means shortening flight distance.

For example, we will not able to fly from Istanbul to London non-stop. We will have to land somewhere between to refuel. This is a waste of time, which means the extension of the journey. In addition, additional landing and departure fees mean taxes and tax extras of the aircraft. All of this is reflected in the ticket prices of the passengers. What can we do then?

It is inevitable that we go back to one or several of the previous items and reduce them. We can give up all over the catering. We can reduce the cargo capacity to half or we can totally give up the extra cargo. We can reduce the number of toilets and accept a little longer queues. We can reduce the luggage limit per passenger. All these options depend on the decisions of the operator.

Here in this example, the competition in the air is limited to 41000 kg. Whichever airplane it is, the numbers might have varied but the limits are set. Competition in the air depends on the proper management of the options in this range.