DALLAS — A winter storm caused flight interruptions across the country on Wednesday, but ice and snow were only part of the battle for Dallas-based Southwest Airlines.

The airline cancelled about 450 flights system-wide, and, in an email said the “vast majority” of those cancellations were due to weather; about 40 were because of maintenance issues.

The airline experienced almost 700 delays, according to the flight tracking website FlightAware. Southwest did not offer a breakdown of the causes of those delays.

A company spokesman said double the normal of planes were out of service on Wednesday due to maintenance issues, and that is the source of what has become a public airing of grievances. Southwest is calling into question whether a labor dispute is behind it all.

“I think the passengers may be caught in the middle here because of the ongoing contract dispute, but when you’re dealing with flying, it’s not like riding in a bus where you can pull over if you have an incident,” said Billy Clark, a retired U.S. Air Force major who flew military planes for 22 years. 

He is now an aviation attorney in Dallas.

Southwest is in the middle of contract negotiations with AMFA, the Aircraft Mechanics Fraternal Association, which represents about 2,400 mechanics. 

Southwest Chief Operating Officer Mike Van de Ven said the increase in aircraft being taken out of service began after the airline’s latest round of negotiations with AMFA. Van de Ven said AMFA has a history of work disruptions.

The maintenance issues led Southwest to declare an “operational emergency” in Dallas and three other cities, according to the airline. That declaration puts tight restrictions on maintenance workers – including when they can turn down overtime and take time off work.

AMFA calls that intimidation. 

AMFA said recent news reports that brought nationwide Southwest safety concerns to light helped mechanics feel “less fearful” about writing up legitimate issues.

“No matter how small an issue we may find with an aircraft, we have an obligation mandated by operation of our FAA issued licenses to repair it and make the aircraft airworthy,” AMFA president Bret Oestreich said in a statement.  

“It is our hope that the Southwest management will join this commitment to restoring our safety culture and looking at this transition not as an “operational emergency” but rather the beginning of a new normal.”

Clark said Southwest has an obligation to thoroughly address any and all maintenance issues.

“Southwest has a strong record of being one of the safest airlines around. With that being said, passengers to have a right to be concerned,” he said. “But the pilot, as aircraft commander, has the ultimate responsibility on whether that plane is going to fly.”