China plane crash: What happens when an aircraft fly close to the speed of sound?

Beijing, Mar 23: The China Eastern Airlines Corp, which crashed on Monday was travelling close to the speed of sound moments before it rammed into a hillside, a review of the flight track data by Bloomberg News said.

The Boeing C. 737-800 was flying through the air at over 966 kilometres per hour and at times may have even exceeded 700 mph, data by Flightradar24 said. The black boxes from Flight 5735 haven't been recovered.

Pilots of a doomed China Eastern Airlines Corp. flight also failed to respond to calls from air-traffic controllers after tipping into a deadly nosedive, authorities said.

What is speed of sound?

Air is a gas, and a very important property of any gas is the speed of sound through the gas. According to NASA, the speed of "sound" is actually the speed of transmission of a small disturbance through a medium. Sound itself is a sensation created in the human brain in response to sensory inputs from the inner ear.

Disturbances are transmitted through a gas as a result of collisions between the randomly moving molecules in the gas. The transmission of a small disturbance through a gas is an isentropic process. The conditions in the gas are the same before and after the disturbance passes through. Because the speed of transmission depends on molecular collisions, the speed of sound depends on the state of the gas. The speed of sound is a constant within a given gas and the value of the constant depends on the type of gas (air, pure oxygen, carbon dioxide, etc.)

So what happens when an aircraft approaches the speed of sound?

When aircraft first approaches the speed of sound, these effects are seen as constituting a barrier, making faster speeds very difficult or impossible.

The term sound barrier is still sometimes used today to refer to aircraft approaching supersonic flight in this high drag regime. Flying faster than sound produces a sonic boom.

The sonic boom occurs as the aircraft reaches the speed of sound. The speed of sound changes with altitude and temperature. At sea level and standard atmospheric conditions, the speed of sound is 345 meters per second (equivalent to 770 mph or 1239 kph). At 35,000 feet, this could be reduced to around 295 meters per second (660 mph or 1062 kph).