DALLAS (CBSDFW.COM) – Southwest Airlines is still working under an operational emergency which started Friday, February 15.

The Dallas-based airline said Monday it continues to have twice as many jets as normal out of service for maintenance.

CBS News reports Southwest has cancelled about 100 flights since Friday because of maintenance.

The airline said about 40 of its aircraft had to be taken out of service temporarily Monday to be fixed.

Normally, Southwest said it expects up to 20 aircraft to be out of service each day.

It operates about 750 jets.

The airline said there is no common reason for the reported maintenance issues, but said it’s trying to make sure that all of its mechanics scheduled to work come in.

A view of a Southwest airlines jet. (credit: Bruce Bennett/Getty Images)

On Friday, CBS News reported the airline sent a memo to mechanics, calling the situation an “operational emergency” and that the mechanics union expressed concerns members could be fired for unexcused absences.

John Goglia, a former member of the National Transportation Safety Board told CBS News, “This kind of stress on the operation is not good. It doesn’t bode well for the safety of the airline.”

In a statement Monday, Southwest said, “We continue to require all hands on deck to address maintenance items so that we may promptly return aircraft to service. At the same time, our operational planners are actively working in the background to minimize the impact to our Customers.”

Weather has also been an issue for Southwest for the past couple of days.

On Sunday alone, the airline said it cancelled 100 flights, most because of the weather and that fewer than 20 flights were cancelled because of maintenance.

An airline spokeswoman said 80 flights were cancelled Monday, mostly to reposition aircraft from Sunday’s weather.

But the uptick in jets that are out of service comes after a CBS News investigation in which some Southwest mechanics complained the airline pressured them to return aircraft to service faster.

The mechanics are still working under their old contract and have been negotiating a new one with the airline for six and a half years.

Captain Dave Hunt, Senior Director of Safety Management at Southwest Airlines said, “I have the highest confidence in the work that our AMT’s and our mechanics do. And also that any issue that’s brought up, any issue, is dealt with appropriately.”

The CBS News investigation prompted two Democratic lawmakers in Congress to recently write the FAA a letter asking the agency how its addressing the report.

The FAA has teams of inspectors at not only Southwest Airlines, but all of the airlines to ensure safety.