Why satellites? As mentioned by others, they are expensive and low-bandwidth. The airliners already broadcast their location and speed to other planes around via ADS-B. Now improve the system slightly - have the airplanes record all received ADS-B messages. Once a plane goes missing, investigators can collect the recordings from planes that were nearby, and review the last ADS-B messages from the missing plane. This is both relatively cheap to implement and should pinpoint the last location with much better accuracy. The airplane should also have better chances at transmitting ADS-B broadcast than a directed signal to a satellite while under heavy turbulence or being upset.