The Federal Aviation Administration (FAA) on Friday announced that it will fine Boeing $19.7 million for installing heads-up displays in the cockpits of 791 aircraft that were not certified as compatible with sensors on the aircraft.

The heads-up displays are optional equipment — tinted pieces of glass just above the pilot’s eye level that display key data such as airspeed and altitude.

They allow the pilot to read the data without looking down at the instrument panel. The data is fed to the display from standard sensors on the airplane’s exterior, such as the altimeter and the angle of attack sensor.

However, only specific sensors are tested and approved as compatible with the heads-up display.

Between June 2015 and March 2019, the FAA said Boeing installed the heads-up displays, made by Rockwell Collins, on 618 Boeing 737 NG aircraft and 173 Boeing 737 MAX aircraft with sensors that were not listed as compatible.

Boeing’s engineering staff and its authorized representatives who report to the FA failed to verify the compatibility of the sensors.

As a result, the FAA said, “Boeing failed to maintain its quality system” and “the aircraft were unworthy.”

Boeing has 30 days to pay the fine or negotiate a reduction.