Nearly two dozen Southwest Airlines 737s sidelined over a maintenance issue are back in service, NBC News learned Friday.
NBC News confirmed through government sources the Dallas-based airline pulled 22 of their Boeing 737s out of service on the belief that the wrong O-Rings were installed on some engines.
Southwest confirmed to NBC 5 that no leaks were found in any of the fuel pumps and that all aircraft have been returned to service.
"Southwest Airlines made the FAA aware of a maintenance issue involving the suitability of engine O-rings on a limited number of the company’s aircraft. Southwest removed those planes from service while the airline completed the necessary repairs. The FAA was in contact with Southwest as part of the agency’s ongoing airline safety oversight program and closely monitored the situation," the FAA said.
NBC aviation expert John Cox said the O-Ring in question most likely keeps oil from bleeding out of the engine and that if it were to escape it could force pilots to shut down an engine.
In a letter to Phoenix Maintenance Teams, Southwest Airlines management wrote: "We have been experiencing an unusually high number of out of service aircraft over the last few days. Due to this number of out of service aircraft, out operation requires all of our scheduled aircraft maintenance technicians and inspectors. I am declaring Phoenix in a state of Operational Emergency effective 10 a.m. central time (Friday)."
In an emergency, a 737, the only aircraft Southwest flies, can fly on one engine.
In a statement to NBC 5 the airline said on an average day they plan for as many as 20 of their 750 aircraft to be unexpectedly out of service for maintenance items. Southwest added that they did have more maintenance issues this week than normal, but that there was no common theme among the reported issues and that they brought in more staff to promptly return the aircraft to service.
At the same time, Southwest said operational planners were working in the background to minimize the impact to travelers.