Based on the lack of warning sounds on the CVR, the NTSB also determined that the plane's take-off warning system (TOWS), designed to alert the crew if the engines are throttled to take-off power without the flaps and slats being correctly set, failed to alert the pilots to their improper takeoff configuration. The switch that operated the TOWS in the incident aircraft had been previously modified, per Boeing instructions, to prevent nuisance activations during aircraft taxiing. A fleet-wide Boeing 727 inspection, ordered by the Federal Aviation Administration following the Flight 1141 crash, identified 35 anomalies in the TOWS out of 1,190 aircraft examined. The FAA had recommended that the Boeing 727 TOWS be changed from a system activated by the aircraft throttles to one activated by engine pressure ratio (EPR), and while Delta owned Boeing 727s that had an EPR-activated TOWS, these were all aircraft that Delta had acquired from other airlines, and Delta did not convert its own aircraft to an EPR-activated system. The NTSB concluded that the TOWS had not activated because it had an intermittent problem that was not detected or corrected during the aircraft's last maintenance action.