As commercial aircraft have gotten larger and heavier, their landing speeds have gotten higher and higher as well. This has made bringing aircraft to a stop more difficult, as these aircraft require longer and longer landing strips. In many cases, brakes can no longer be solely relied upon to slow the aircraft. Therefore, many commercial aircraft now use thrust reversers. Thrust reversers, as their name implies, reverses the thrust generated by the engines to slow the aircraft. Thrust reversers come in two categories: mechanical blockage, and aerodynamic blockage.