A United Airlines flight from Houston to San Francisco has diverted to Albuquerque, New Mexico, after the co-pilot passed out.
Albuquerque airport spokesman Dan Jiron said air traffic controllers got word shortly after 8am local time that the plane would be landing after the first officer, who is second in command, had a medical episode.
The plane landed without incident about 20 minutes later.
Mr Jiron said the co-pilot regained consciousness and was able to walk off the plane to be transported to hospital. There were no details about his condition or what may have caused the episode.
United said it was aware of the diversion but had no further comment.
The incident came a day after an American Airlines captain became gravely ill while flying from Phoenix to Boston and later died.