U.S. aviation regulators are reviewing a request by Boeing Co. to redesign engine covers on the 777 and 737 jet models that have led to multiple dramatic failures, including a passenger death in 2018.

The Federal Aviation Administration is considering Boeing’s petitions to make “safety improvements” on the front of jet engines on the two models, the agency said in the Federal Register Wednesday.

Federal regulations require that engines are encased in a shield to prevent damage to a plane when a fan blade fails, but in multiple incidents on certain 737s and 777s blade fragments bounced forward and damaged less protected areas.

The proposal is the first step in getting government approval for strengthening the engine covers. Because current regulations on the so-called cowling at the front of the engines don’t require the fixes, the company is requesting an exemption to the rules to proceed with its redesign.

The aviation industry and the public will have 20 days to comment on the FAA’s proposal to grant Boeing the exemptions.

Boeing didn’t immediately respond to a request for comment.

The work on the engine covers was prompted by a series of incidents on Next Generation 737s and 777s with Pratt & Whitney engines in recent years.

A woman aboard a Southwest Airlines Co. 737-700 over Pennsylvania died on April 17, 2018, after a fan blade fractured and sent debris into the window next to her seat.

In another incident this past Feb. 20, after a fan blade broke loose on a United Airlines Holdings Inc. 777, it triggered a massive failure that sent metal shards raining on neighborhoods and prompted an emergency landing. Nobody was seriously injured.