Nature vs. Nurture: Did the Blizzard or Federal Rules Cause Massive Flight Cancellations?

Charges have been flying that airlines prematurely canceled flights ahead of the East Coast snowstorm because of new rules fining airlines for leaving planes standing idle on tarmacs, though transportation experts say that such claims are impossible to quantify.

In April, new rules went into effect that threatened airlines with a $27,500 per passenger fine if their planes didn't take off within three hours after pulling out to the tarmac. The move was aimed at reducing a spate of horror stories from people stuck in claustrophobic conditions on planes without access to bathrooms, water or food.

The regulation seems to have had its desired effect. According to the Department of Transportation, since new rules were enacted in late April, the number of tarmac delays over three hours has dropped considerably. From May to September 2009, 535 tarmac delays over three hours were reported; in May through September this year, the number was 12.

But after an East Coast storm threatened to ravage New York area and other airports, hundreds of flights to and from the region were cancelled – several even before the snow started to fall -- and complaints are mounting that the airlines were deserting their customers for fear of racking up fines.

"There's no doubt about it, airlines (were) pre-emptively canceling flights because they don't want to be stuck paying $27,000 per passenger," said Vaughn Cordle of Airline Forecasts.

"I think it's safe to say that there are many passengers who would have reached their destination, albeit with non-trivial delays, had the ... ruling not be in effect," said Amy Cohn, an associate professor of industrial and operations engineering at the University of Michigan and an affiliate at MIT's Global Airline Industry Program.

But David Castelveter, a spokesman for the Air Transport Association, said while anecdotally, the airlines have changed their behavior as a result of the rules, the cause-effect relationship in this case is unlikely.

"The greatest number" of cancellations was "truly driven by the weather," not the the new tarmac rules, he said.

After the Midwest storm delays a few years back, Northwest Airlines said it would pre-emptively cancel more flights during bad weather to keep passengers from waiting for long periods in the airport, Castelveter said. This was before the new regulations.

Airline analyst Darryl Jenkins said snowstorms are fairly easy to predict so airlines cancel flights ahead of time so as not to drag people to the airport just to strand them there.

"Don't think the regulations made any difference in this event," Jenkins said

A Department of Transportation official said the department does not get real-time information -- it receives monthly reports -- so it's too early to say how many cancellations and delays occurred over the last couple of days.

But in response to critics who feared the pendulum would swing too far to the other side after the new rules were enacted, the official said overall, the number of cancellations has not gone up significantly. In 2009, 220 flights were cancelled after delays of two hours or more compared with 225 flights in 2010 -- a difference of five flights.

Cohn said it's too early to know the data on how the law impacted airline behavior during the recent blizzard, but with the post-Christmas upswing in passengers, potential delays were too costly to risk.

"The per-passenger fine is too high -- especially with virtually every seat filled on the post-Christmas flights -- and there is too much uncertainty about when the (Transportation Department) would and would not impose fines for airlines to gamble on," Cohn added.

Cohn said she suspects that most flights with tarmac delays that would be eligible for fines will be exempt because they're international flights or there was no safe way to disembark passengers, a factor she called a major paradox to the new rules.

"During those times when three-plus hour delays are most likely, the airlines often do not have the ability to de-board passengers safely and thus the ruling doesn't apply," she added.

Cordle said while the fines have reduced three-hours delays, an increasing number of delays under three hours do impose a massive cost  -- to consumers.

FoxNews.com's Sharon Kehnemui and Fox Business Network's Rich Edson contributed to this report.