A user on a social network asked a question that seems logical at first glance, but the answers from aviation specialists reveal a complex equation: fuel cost is just one piece of the puzzle. Time, crew salaries, and operational efficiency dictate cruising speed.

A question that seems simple – why do passenger planes fly at 1000 km/h when fuel consumption would be lower at 600 km/h? – has generated detailed responses from aerospace engineers and aviation specialists. Their conclusion is that an airline’s economy is not just about litres of kerosene. It’s about a complex calculation in which time, fixed costs, and productivity are equally important.

The optimal speed is not the lowest speed

One of the first factors cited by specialists is that fuel economy is not directly proportional to speed reduction. As an engineer explains, in aviation, drag has two components:

• Parasitic drag – which increases exponentially with speed.
• Induced drag – related to lift generation, which decreases as speed increases.

At low speeds, induced drag is high. At high speeds, parasitic drag dominates. There is a balance point, called the “optimal cruising speed,” where fuel consumption per kilometre is at its minimum. Specialists calculate this point with precision, and it is not at 600 km/h, but much closer to the actual cruising speed (800-950 km/h).

How much fuel does a plane really consume?

An expert provides a concrete example, based on data from a Boeing 747:

• At 920 km/h (normal cruising speed), consumption is 12,500 litres per hour, or 13.6 litres per kilometre.
• At 600 km/h, hourly consumption drops to 7,800 litres, but consumption per kilometre drops only to 13 litres – a difference of just 0.6 litres per kilometre.

In other words, reducing speed by one-third brings a saving of only 4-5% per kilometre, but flight time increases significantly.

The economics of flight: the cost of time

This is the essential part of the answer. Another specialist explains that an airline must take into account:

• Crew costs: pilots and cabin crew are paid by the hour. If a flight takes 30% longer, staff costs increase by 30%.
• Aircraft productivity: a slower plane can make fewer flights per day. An aircraft flying 10,000 hours per year could lose 3,000 flight hours if speed is reduced, dramatically reducing revenue.
• Capital costs: aircraft are extremely expensive. Airlines must use them as intensively as possible to recoup their investment.

One specialist calculates that crew costs represent about one-third of total costs. Therefore, a 30% reduction in speed would increase crew costs by 30%, leading to a decrease in profitability of up to 40%.

The technical factor: altitude and the sound barrier

Besides economics, there is also a physical limitation. Planes fly at high altitudes to reduce air resistance (air is thinner). However, at very high altitudes, the speed of sound is lower, and planes are not designed to exceed it. Also, at those altitudes, the margin between the minimum speed (above which the plane stays airborne) and the maximum speed (before entering the dangerous sonic zone) narrows, leaving little room for variation.

Conclusion: current speed is the result of an economic calculation

So the answer is that the current cruising speed (800-950 km/h) is the result of a compromise between fuel consumption (which is only slightly higher at high speed) and operational efficiency (which drops dramatically at low speed). Airlines do not fly at 1000 km/h because they are irresponsible, but because, at this moment, this is the speed that allows them to be profitable and offer passengers a fast and affordable service.