(CNN) -- Only 20 tarmac delays of more than three hours were reported in the year after the Department of Transportation's tarmac delay rule was implemented, according to DOT figures released Tuesday.
In the year leading up to the rule, from May 2009 to April 2010, 693 delays of more than three hours were reported. After the rule was instituted on April 29, 2010, the number of delays exceeding three hours plummeted to 20 between May 2010 and April 2011.
"It's clear that we've accomplished our goal of virtually eliminating the number of aircraft leaving travelers stranded without access to food, water or working lavatories for hours on end," said U.S. Transportation Secretary Ray LaHood in a statement.
The tarmac delay rule carries the possibility of stiff fines for airlines if passengers are stuck on the tarmac for more than three hours on domestic flights. No fines have been levied since the rule was implemented, according to the DOT.
The agency has opened investigations into 183 allegations of violations of the rule. "The vast majority of these investigations involved complaints filed by consumers that we determined were not violations of the three-hour limit or other provisions of the tarmac delay rule," said DOT spokesman Bill Mosley in an e-mail.
Critics of the rule said flight cancellations would spike as airlines tried to avoid penalties. DOT figures show that the number of flights canceled after tarmac delays of more than two hours -- "those most likely to be canceled to avoid violating the rule" -- increased slightly, from 336 the year before the rule to 387 between May 2010 and April 2011.
Consumer advocate Kate Hanni, who founded FlyersRights.org to urge the government to provide airline passenger protections, called the rule a "huge success."
"And the predictions of the airlines that there would be an "Armageddon" of flight cancellations did NOT materialize," Hanni said via e-mail.