Police arrested two pilots Saturday for suspected intoxication before they were supposed to fly from Scotland to the United States, according to airline officials.

The two pilots for United Airlines were arrested at Glasgow Airport resulting in their flight being delayed for 10 hours while the airline found replacement pilots.

The incident comes barely a month after two Canadian pilots for Air Transat were arrested at the same airport under the same charges.

“This is very rare. Two in about a month is very, very unusual,” Kyle Bailey, an aviation analyst, told CTV News Channel. “This is just a couple of bad apples, a couple of bad instances that happened.”

According to Bailey, there’s typically an eight hour “bottle-to-throttle” rule, although it varies by country and by airline. The rule means a pilot’s last drink must be eight hours before operating a plane. In the U.S., a pilot’s blood alcohol content has to be a 0.04 or higher to be in violation of the “bottle-to-throttle” rule.

“A pilot just can’t go into a bar in an airport, it’s against airline company policy to be inside a bar at an airport because you’re conveying a bad reputation to the airline,” said Bailey.

Bailey also said that the pilots will most likely be blacklisted from ever holding a flying job or simply flying a plane again if they are found guilty of intoxication before flying.

“Usually one pilot is the check on the other,” said Bailey. “But when you have both of them allegedly drinking it does raise serious concerns.”

Both pilots are expected to be arraigned on Monday at a court in a Glasgow suburb to face the charges connected to Britain’s transport safety laws.

With files from the Canadian Press