After gaining nearly 14% on Monday on news that Pfizer and BioNTech's COVID-19 vaccine is over 90% effective, Boeing (NYSE: BA) is indicated to open another 4% higher Tuesday on reports the U.S. Federal Aviation Administration (FAA) is preparing to lift the grounding order on 737 MAX.

Yesterday's move was the biggest single-day gain since June and followed hopes that life could get back to normal sooner rather than later, which means more airline flights and thereby more plane orders.

Today's boost was driven by a Reuters story that the U.S. Federal Aviation Administration (FAA) is preparing to lift the grounding order on 737 MAX planes as early as November 18.

The regulatory body is now in the final stages of reviewing proposed changes to 737 MAX with expectations that the process will be completed in the coming days.

"The FAA continues to engage with aviation authorities around the world as they prepare to validate our certification decision," FAA Administrator Steve Dickson said.

"As I have said many times before, the agency will take the time that it needs to thoroughly review the remaining work. Even though we are near the finish line, I will lift the grounding order only after our safety experts are satisfied that the aircraft meets certification standards."

Once the approval is granted, airlines using 737 MAX will have to complete software updates and fresh pilot training before planes can be ungrounded. Southwest Airlines, the world's largest MAX operator, noted it will likely need several months to comply with the new FAA requirements. The airline said it doesn’t expect to use 737 MAX until the second quarter of 2021.

FAA grounded 737 MAX on March 13, 2019, after it found similarities in two fatal crashes that killed 346 people.