A key safety system was turned off in a US army helicopter when it crashed into an American Airlines flight last week, killing 67 people. Ted Cruz, the chairman of the Senate commerce committee, told reporters that the Black Hawk helicopter had switched off an advanced surveillance technology known as automatic dependent surveillance-broadcast (ADS-B). “This was a training mission, so there was no compelling national security reason for ADS-B to be turned off,” Mr Cruz said on Thursday, following a briefing from federal transport bodies.