Lawmakers requested documents on Friday from Boeing about a faulty cockpit alert on the manufacturer's beleaguered 737 Max planes — an issue the company knew about for more than a year before informing regulators and didn't plan to fix for three years.

Rep. Peter DeFazio, an Oregon Democrat and chairman of the House Committee on Transportation and Infrastructure and Rep. Rick Larsen, a Democrat from Washington state who is chairman of that committee's aviation panel, on Friday said they sent letters to Boeing as well as United Technologies and the Federal Aviation Administration seeking documents and a timeline of when they became aware of the issue and when airlines were informed.

"The fact that Boeing knew about a defect for more than a year before disclosing it to the FAA is of great concern to me, which is why Chair Larsen and I are asking for further documentation to get a more fulsome picture of who knew what and when," said DeFazio in a statement. "It's critical we leave no stone unturned during our committee's investigation."

Aviation officials in March grounded the Boeing 737 Max jets around the world after a second fatal crash of the popular aircraft within five months. A total of 346 people were killed in the two crashes.

Investigators looking into the crashes have implicated an automated anti-stall system aboard the jets that was fed bad sensor data, sending the planes into fatal dives.

The cockpit alerts in question let pilots know if sensors on the plane aren't functioning properly. The sensors are meant to determine the angle at which the plane is flying.

The lawmakers said they have received information that suggested Boeing had planned in November 2017 to defer the software update to fix the issue by three years, a timeline Boeing confirmed on Friday in a statement.

Boeing sped up this fix after a Lion Air 737 Max crashed in October 2018, the lawmakers said.

The Chicago-based manufacturer said the lack of this indicator, known as the angle of attack disagree alert, "did not adversely impact airline safety or operation.

"Based on the safety review, the update was scheduled for the Max 10 rollout in 2020," Boeing said in a statement, referring to the largest model of the 737 Max it is developing. "We fell short in the implementation of the AoA disagree alert and are taking steps to address these issues so they do not occur again."

Acting FAA chief Daniel Elwell told the House committee's aviation panel last month that he was "not happy" with the 13-month gap between the time Boeing found the problem and when it informed regulators.

The House committee is planning on holding another hearing on June 19 about the 737 Max, which is set to include testimony from pilots and flight attendants, according to people familiar with the panel's plans.