Southwest Airlines faces "operational emergency"

President's week has been tough for Southwest Airlines. Since Friday, the carrier has experienced more cancellations and delays than any other US airline. About 100 flights were canceled for maintenance reasons, as the airline struggled to cope with the unusually high number of aircraft taken out of service for maintenance reasons.

In total, more than 40 aircraft per day were decommissioned, more than double the usual average, and about 5% of the fleet of about 750 Southwest aircraft.

Southwest is facing what its own managers call a state of operational emergency, due to the unusually high number of Boeing 737 aircraft taken out of service for maintenance purposes.

In a memo obtained by CBS News, the airline asked everyone to stay on deck and warned that maintenance employees could be fired for unmotivated absences.

The out-of-service aircraft outbreak follows our "CBS This Morning" investigation after mechanics' complaints about excessive pressure to get the aircraft up and running faster, reports correspondent Kris Van Cleave.

This motivated the Friday letter "state of operational emergency".

Such a statement is not unprecedented, but it is rare.

"I think that's an indication of problems," said John Goglia, a former member of the National Transportation Safety Board. "This kind of stress on the operation is not good.That does not bode well for the safety of the airline."

A dozen southwest mechanics tell CBS News colleagues to feel emboldened to write problems following our investigation earlier this month in allegations of negative pressure on the mechanics of Southwest.

Last week, Southwest also had to check 22 engines to make sure that the proper seals (or O-rings) of the fuel pump were installed.

The memo on "the state of operational emergency" arrived just days after Senators Ed Markey and Richard Blumenthal sent a letter to the FAA for information on its monitoring of Southwest as a result of our investigation.

"Captain Dave Hunt, senior manager of safety management at Southwest, has always told us that safety is our priority," said last month. "I have the utmost confidence in the work of our mechanics and in the fact that any problem raised, all question, is treated appropriately ".

The airline is stuck in strained contract negotiations with mechanics that have been going on for years. The union of mechanics worries about the memo about Southwest 's state of emergency and its "threat of termination". The memo gives the airline the ability to assign longer work hours and change staffing assignments.

The union fears that it "increases the level of restraint and does not further degrade safety", because "technicians will be forced to work overtime regardless of their … fatigue".

In a statement, Southwest says it is working to minimize the impact on customers of out of service aircraft.

The FAA claims to monitor the situation closely.