U.S. Reps. Peter DeFazio of Oregon and Rick Larsen of Washington sent letters to Boeing and the Federal Aviation Administration seeking details on what they knew when, and when airlines were told.
The feature is designed to warn pilots when a sensor provides incorrect information about the pitch of the plane’s nose.
Boeing admitted in May that within months of the plane’s 2017 debut, engineers realized that the sensor warning light worked only when paired with a separate, optional feature.
The sensors malfunctioned during flights in Indonesia and Ethiopia. Both planes crashed, killing 346 people in all.