Some people did not like the sonic booms caused by Concorde flying faster than the speed of sound. They also complained of the noise Concorde made when taking off and landing. It was twice as loud as conventional passenger jets. Concorde was not allowed to fly over certain countries because of this. There were also concerns that having many Concordes in the air at once could damage the ozone layer. The price of fuel increased many times in the 1970s, but the Concorde also consumed much more fuel than a conventional passenger jet.