Passenger planes fly slower today than before, why is that?

It is a little known fact that passenger planes today fly slower than they used to. For example, the Concorde could reach speeds of 2,000 km/h in the 1970s, more than twice as fast as today's commercial aircraft. Or in 1996, a British Airways plane took only 2 hours and 53 minutes to fly from New York to London, but today the same route can take passengers no less than 6 hours in the air, about twice as long. Why is that?

The current speed of passenger planes is about 640 - 965 km/h. But in the past, there were two types of civil aircraft, the Concorde of the UK and France and the Tupolev TU-144 of the Soviet Union, which could reach a speed of 2,500 km/h at an altitude of 20,000m. The average speed of the Boeing 707 in the 1960s was 972.3 km/h, faster than the speed of sound (800 km/h).

There are many reasons why these two types of aircraft are not used today. High speed makes landing many times more dangerous. The higher the speed of the aircraft, the more fuel is consumed and the life of the aircraft engine is greatly reduced.

In addition, high speed will create engine noise that is annoying to passengers as well as people in the area near the airport.

Nowadays, with the advancement of science and technology, supersonic commercial flights are being tested again and there are many signs of feasibility. Studies show that modifying the shape of an aircraft can reduce the impact of a sonic boom by ⅓.