The Air Force on Monday acknowledged a human error involving an outdated test answer key corrupted this year’s technical sergeant selection process, forcing officials to revoke 135 promotions and award those slots to other troops who rightfully earned them.

The error affected only the service’s security forces career field, where officials rescored all 2,285 eligible airmen after discovering an outdated scoring key had been used on the Specialty Knowledge Test.

“We owe it to those affected to address it immediately,” Chief Master Sgt. of the Air Force David R. Wolfe said in a statement. “This is going to be hard for everyone impacted.”

After rescoring all 2,285 eligible airmen, the Air Force determined that 451 previously selected airmen would keep their promotions while 135 others no longer met the cutoff score. Another 135 airmen who were initially passed over will instead receive the promotions after officials rescored every eligible test.

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Air Force officials said the error was discovered after the promotion list was released and an enlisted promotions team member at the Air Force Personnel Center identified the outdated scoring key. Officials described the mistake as an isolated and unprecedented human error, adding that no other Air Force specialty codes were affected.

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Officials said they verified the correct answer key with subject matter experts before rescoring every eligible exam. The total number of promotions did not change, remaining at 586.

“We promote Airmen based on merit, which is established in federal law and policy,” Lt. Gen. Jefferson O’Donnell, the Air Force’s deputy chief of staff for manpower, personnel and services, said in a statement. “Who we are as an Air Force, defined by our core values, demands integrity in the meritocratic promotion system.”

The Air Force Personnel Center plans to announce the 135 newly selected technical sergeants in a supplemental promotion release during the week of July 13. Officials said the new selectees will receive adjusted line numbers that will not affect when they are promoted.

The Air Force said it has tightened its review process and is examining how the error occurred to prevent a similar mistake in future promotion cycles. Leaders are notifying affected airmen directly and have set up a hotline to answer questions.

Officials said the mistake was caused by human error, not artificial intelligence.