Why Do Most Commercial Aircrafts Fly Subsonic?
It may be surprising to most that planes have been getting slower and slower since the 1970s. A JFK-LHR flight that used to take under 3 hours with the Concorde now takes more than 6 hours. In the golden age of air travel, everything was about faster, higher, further. This led to the supersonic travel race between Aérospatiale/BAC’s Concorde and the Tupolev Tu-144. However, in the modern era, most airlines prioritize fuel efficiency and cost savings over speed, as the market for supersonic travel diminished.
Typical commercial airplanes are not designed to fly faster than the speed of sound (Mach 1). If commercial planes fly faster than their designed speed, air begins to form shockwaves along the wing, which may cause the aircraft to be uncontrollable. This speed that planes cannot exceed during any stage of flight is called the Maximum Mach Number.
Expenses of Flying Supersonic
Although achieving high speeds is always desirable, supersonic flight require a myriad of expenses. Supersonic planes need larger and heavier engines, often paired with afterburners. Afterburners drastically worsen the fuel consumption of the aircraft, making their fuel economy horrible (I wrote another article on engines for supersonic transport + afterburners!). Supersonic aircraft like the Concorde are also extremely inefficient to operate: first of all, due to the intricate engineering behind every aircraft, the list price of supersonic aircraft is already high. Not only that, not many airports were certified to operate supersonic aircraft due to their runway length(s) being too short. Many countries also had sound regulations in place which prevented the operation of supersonic aircraft.
In contrast, flying subsonically increases range, efficiency, and causes less harm to the environment.
All of these costs stack up to ticket prices that not many people could afford. As a result, supersonic flights started to fade away as more people converted to slower, cheaper flights instead.
Flying Slower Saves Fuel
One extra point: flying slower (even just a tiny bit slower) saves fuel.
When planes are taking off, throttles are usually set to TO/GA (which stands for Take Off/Go Around), or 100% throttle. After takeoff, however, the throttle is usually reduced to 70% to 80% and maintained throughout the duration of the flight.
As an example, jetBlue and RyanAir both have asked their pilots to fly a little slower to save fuel. jetBlue is thought to have saved $13.6 million just by flying two minutes slower per hour.
The Future
While it’s certain that most commercial planes nowadays are subsonic, the future is bright for supersonic travel. The Boom Overture, developed by Boom Supersonic, is a supersonic passenger aircraft scheduled to enter service by 2029. Innovated with new technologies and powered by sustainable aviation fuel, there’s no question that supersonic travel will be more and more accessible in the next few decades.
