'Don't sink, don't sink, don't sink.' Boeing didn't fully test how pilots would respond to warning system

The National Transportation Safety Board is criticizing Boeing for failing to fully test the MCAS flight control system believed responsible for two fatal crashes of the 737 Max.

The agency says one thing that Boeing failed to examine was the effect on pilots of the warning alerts that MCAS would trigger.

A plane in trouble has a very loud cockpit. The NTSB says the pilots of the two downed planes experienced multiple alerts at the same time.

The control yoke was shaking. Then a clacking sound warned the plane was gaining too much speed and heading toward the ground: "Don't sink Don't Sink Don't sink. Terrain terrain terrain terrain."

The NTSB has seven recommendations for testing that would take human responses to these alarms into account. And it said new tests should be conducted on the Max before it's allowed to fly again.