German police entered the cockpit and found the 40-year-old in a “highly intoxicated condition” on Friday evening, a statement said.
An airport official had sounded the alert after finding the Portugalia pilot “reeking of alcohol and walking unsteadily,” it said. Portugalia is a subsidiary of the national carrier TAP.
Stuttgart prosecutors immediately suspended the co-pilot's flying licence and fixed a 10,000-euro ($12,000) bail.
Portugalia cancelled a flight from Stuttgart to Lisbon on Friday night with 106 passengers.
TAP said it would “open an enquiry and take necessary measures” and apologised to passengers for the inconvenience caused.