"United Airline's decision today was a voluntary measure on United's part. It is related to ensuring compliance with an Airworthiness Directive," said Ian Gregor of the FAA.
The temporary grounding caused at least 17 flights to be canceled and an unspecified number of delays. Maintenance checks take 60 to 90 minutes.
About 10 flights at LAX were delayed, a few canceled. On the monitors, "aircraft servicing" showed as the reason.
Although the airline said the checks would be completed in 24 hours, the issue could affect United's schedule into Wednesday.
Travelers at LAX said they were glad the airline was taking time to do this, but at the same time, they were concerned with how sudden the maintenance check came.
The Associated Press contributed to this story.