FAA allowed airlines to pick options for Max planes

The US Federal Aviation Administration, or FAA, allows airlines to make minor modifications in previously certified aircraft to meet their operational needs, a rule Boeing followed when building the 737 Max for foreign carriers, aviation analysts have said.

Some airlines chose to purchase the "angle of attack" system display for readings of two sensors and a "disagree light" to be activated if the sensors produce conflicting readings.

The two airlines that suffered fatal crashes, Ethiopian Airlines and Indonesia's Lion Air, reportedly declined to buy the two add-on safety devices that might have helped the pilots keep the doomed Max jets in the sky. A total of 346 people died in the two crashes five months apart.