United Airlines is changing the keypad codes used to open cockpit doors after the previous codes were accidentally posted on a public website.
The airline sent a memo to pilots over the weekend telling them to use "alternative security measures," a spokeswoman said Monday.
The spokeswoman said the breach in security measures was not the result of hacking and did not cause any flights to be delayed or canceled.
"We are working to change the codes on all of our aircraft," added the spokeswoman, Maddie King.
In a statement, the Chicago-based airline said it uses "a number of measures" in addition to the access codes to keep cockpits secure, and it was working to fix the situation as soon as possible.
King said backup procedures had been put in place, but she declined to give details, citing security concerns.
United changes the access codes periodically but scrambled over the weekend after it learned about the information becoming public.
Rusty Aimer, a retired United pilot who is now an aviation consultant, said changing the codes "should not create a big security concern." He added that he could not remember a breach of the secret codes in the years that he worked for the airline.
Security of cockpits was strengthened after the terror attacks in September 2001, during which hijackers took over control of United and American Airlines planes. The Air Line Pilots Association, which represents United pilots, said this weekend's incident showed the need for secondary barriers on all U.S. airliners.
The union has lobbied for legislation in Congress that would require the lightweight screen barriers, which it says would cost $5,000 per plane and slow down would-be hijackers long enough for air marshals or other passengers to stop them. United installed the screens on some planes after 9/11 but removed them in 2012 to reduce costs, according to the union.
Airlines have procedures for opening the cockpit door, such as when a pilot needs to use a restroom in the main cabin. Flight attendants will often use a beverage cart to block the aisle until the door can be closed.