Because of the pandemic, flights that have not been canceled at all are only operated with a couple of passengers on board.
Apart from obvious financial losses and environmental concerns, flying on empty aircraft causes other problems. For example, purely physical problems – related to weight and balance.
When only a few people fly, passengers are either evenly seated in the cabin or added to the luggage compartment to balance their weight.
In a highly simplified scheme, the aircraft is arranged like a giant swing. By default, the center of gravity of the aircraft is near the main landing gear. But in fact it turns out that the center of gravity of a particular aircraft on a particular flight can shift – because of the passengers, luggage, fuel. The center of gravity changes even during one flight.
Before departure the operator calculates the take-off weight – he takes into account the weight of the empty aircraft, passengers, luggage, cargo and fuel. This is to determine the center of gravity of the aircraft as accurately as possible.
For example, the Embraer E175 has engines in front of its wings, so its center of gravity is closer to the front of the aircraft. As the fuel burns, it shifts towards its tail.
Before departure, the airline’s dispatcher gives the pilot a special uniform that indicates how many passengers will fly, in which part of the cabin – front, middle or rear – they will sit, how much luggage they have and where exactly they will load it. Taking all this information and many other important factors (e.g. the angle of flap deviation) into account, the computer calculates the centre of gravity and take-off speed. Large aircraft such as the Boeing 737 or Airbus A320 usually have no weight or balance problems even when the aircraft is almost empty – if passengers are evenly distributed throughout the cabin. But crews of not so big cars quite often have to transfer passengers.