The ATR72 flight was due to leave Bristol at 5.10pm but was delayed when a new crew had to be flown to Bristol to take over the flight.
The pilot had been involved in a lengthy layover in the airport so was in civilian clothes when he was breath tested. After being found to be over the legal limit to fly, he was arrested under the Railways and Transport Safety Act 2003 for attempting to perform an aviation function while his “ability to perform the function is impaired because of drink”.
He was taken to a nearby police station where he passed a second test and was released without charge.
The alcohol limit to fly is nine microgrammes in a breath test, compared to 35 microgrammes for driving.
Aer Arann pilots and crew do not ordinarily have airport identification for Bristol Airport, as they are normally involved in quick turnarounds and so do not enter the airport.
However, on this occasion, there was a layover of a number of hours.
It is understood this is why the pilot was in civilian clothing and used the passenger security checkpoint rather than the crew entrance.
The incident occurred more than an hour before the flight. Neither the crew nor passengers had boarded the aircraft.
A spokesman for Aer Arann said: “Safety is and always will be our utmost priority. We are taking this matter extremely seriously and a thorough investigation has already started.”