The Federal Aviation Administration said on Wednesday that Boeing Co is developing a service bulletin instructing airlines to install new flight control computer operational program software in the now grounded Boeing 737 MAX.

The agency said in a bulletin to foreign regulators and airlines that its "ongoing review of this software installation and training is an agency priority, as will be the roll-out of any software, training, or other measures."

Boeing previously said it planned a software upgrade. The FAA and other regulators grounded the flight after two fatal crashes since October.