The other pilot, 45-year-old Dan Kudirka, was released from custody and will not be charged, a Police Scotland spokeswoman told ABC News Tuesday.
The two men were arrested at Glasgow Airport Saturday before boarding flight UA162 to Newark, New Jersey, that was set to depart at 9 a.m. They had been held under the section of a transportation safety law that covers on the job intoxication and impairment for aviation.
The flight was subsequently cancelled. The passengers on board were provided with hotel and meal vouchers and were to be booked on another flight.
United Airlines said in a statement that the company has "a strict, no tolerance policy for alcohol."
"These pilots were immediately removed from service and we are fully cooperating with local authorities," according to the statement.
The airline declined to say whether Kudirka would remain employed with the company since his release and referred ABC News to the original statement.
Officials did not say what their blood alcohol level was, but the two allegedly failed a breath test. The law states the alcohol limit for pilots is less than half the limit for drivers in Scotland.
ABC News' Chad Murray and Christine Theodorou contributed to this report.