Boeing confirmed Wednesday that it resumed deliveries of the 737 MAX after garnering regulatory approval for a fix to an electrical problem that had grounded more than 100 planes.

The deliveries revive a key revenue stream for Boeing and come after the aviation giant announced on May 13 that it had sent service bulletins to airlines after the Federal Aviation Administration (FAA) approved its fix for the electrical problem.

Both American Airlines and United Airlines have resumed flights on MAX planes affected by the issue, said spokespeople for the carriers.

A Southwest Airlines spokesman said the carrier was still implementing changes in light of Boeing's service bulletin and had not returned its 32 affected planes back to service. 

Boeing announced publicly on April 9 that it had notified 16 airlines flying its 737 MAX planes of the electrical issue, leading to the immediate grounding of the jets and suspensions of new aircraft deliveries.

The FAA described the problem as "an electrical bonding and grounding issue" and said the problem affects three parts of the plane in models built after Boeing made design changes in early 2019.

The electrical issue was a new setback after the MAX was cleared to return to service in November 2020 after a 20-month grounding caused by two fatal crashes.

Boeing also recently resumed deliveries of the 787 "Dreamliner" plane following a suspension last fall to address production problems.

Two senior House Democrats earlier this week announced they were seeking records from the FAA and Boeing on the MAX and 787 issues. 

The lawmakers, transportation committee chairman Peter DeFazio and aviation subcommittee chairman Rick Larsen, cited their report from 2020 on the MAX, which pointed to significant problems at Boeing and in the FAA's oversight of the company.