Federal regulators hit Boeing Co. with proposed fines totaling US$19.7 million for allegedly installing unapproved cockpit equipment in hundreds of 737 Max and Next-Generation aircraft.

The company put the devices into a total of 791 planes even though the aircraft weren’t certified for the devices, the Federal Aviation Administration said in a press release Friday.

The fine would be one of the largest the agency has ever levied.

The charges focus on devices called head-up guidance systems that allow pilots to look through the windscreen while simultaneously seeing their instruments.

Boeing’s best-selling Max jet has been grounded since March 13 after the second fatal crash linked to a safety device on the plane malfunctioned and repeatedly tried to drive down the nose.

The findings “do not involve a safety issue,” Boeing said in a statement. The company didn’t provide sufficient documentation after installing improved parts in the displays, Boeing said.

“We understand the critical importance of compliance with all documentation requirements of the FAA’s certifications,” the company said.

More Penalties?

Boeing may face additional penalties from the FAA in the wake of the 737 Max crashes and issues that have been discovered on the plane.

For example, a cockpit alert that was supposed to be standard equipment didn’t work on 80% of the 387 Maxes the company delivered. The FAA said that the plane was in violation of U.S. rules as a result, in a July letter to lawmakers.

A 2015 agreement to settle other issues could also open the company to other penalties. Boeing paid US$12 million to settle multiple enforcement cases and agreed to pay as much as US$24 million more if it continued violating FAA rules.

The largest fine ever paid in an FAA enforcement action was US$24.9 million by American Airlines, now known as American Airlines Group Inc., in 2013.