Flight 98, carrying 246 passengers and 14 crew members, was diverted as a precaution Tuesday after a passenger called attention to the odor, American Airlines spokesman Ian Bradley told CNN.
Shannon Airport Head of Operations & Services Niall Maloney said such diversions are not uncommon, CNN reported.
The incident occurred as the airline is looking into the cause of a series of problems involving loose seats on its aircraft. The Los Angeles Times reported Tuesday the problem was reported on a flight from Vail, Colo., to Dallas-Fort Worth, after being reported on other flights Monday and Saturday.
The parent company for American Airlines, AMR, filed for bankruptcy in 2011 and the airline recently announced 11,000 layoffs.
American said disputes with labor, including stalled contract talks with the pilots' union, are not behind the problem with seats coming loose in flight.
"Our maintenance teams continue to inspect aircraft in our 757 fleet to determine what caused the issue," company spokesman Kent Powell said.
Robert Gless of the Transport Workers Union of America said problems related to seats are "a management issue related to outsourcing work to third-party facilities" because seat installation work is largely performed by outside contractors.