The FAA began its probe in February 2018, the FAA told CNN Business on Monday.
"Since then, the FAA has directed the development of a comprehensive solution to the methods and processes that Southwest Airlines use to determine these performance data," the FAA said.
The Wall Street Journal first reported the story. It quoted FAA officials and agency documents indicating the airline's employees made mistakes that got pilots to calculate the wrong weight of aircraft at start.
The errors were described as "systemic and significant", which over time causes the reported starting weights to be 1,000 pounds lower than the actual weight of the aircraft. ”
According to the FAA's Weight and Balance Handbook, a safety guideline for aircraft operators may excess weight on a aircraft cause a number of problems, including the need for higher starting speeds, reduced cross-speeds, reduced maneuverability and higher loading on landing gear.
Southwest ( LUV ) said in a statement to CNN Business that there is a "continuous effort to track and voluntarily report operational data to the FAA so that we can mitigate and eliminate any operational risks. "
But the airline added that it has already introduced controls and procedures for solving weight and balance issues. Southwest said it has participated in these measures with the FAA.
"Southwest believes that the controls and procedures we have implemented in 2018 have improved our weight and balance program and solved the issues we originally reported to the FAA," the airline added.
FAA has not linked accidents to the weight differences. But the agency said in its statement to CNN Business that "it will not close its investigation until it is convinced that Southwest's corrective actions are consistent and persistent."
The news about the FAA probe also comes that Southwest is struggling with an "operational emergency" due to a work conflict with mechanics.
Southwest said in a statement to CNN Business on Friday that the percentage of "out-of-service aircraft" with maintenance problems in its fleet had more than doubled over the past week.
"We require all hands on tires to address maintenance items so we can quickly return aircraft for service," a Southwest spokesman said in an email at that time.