Southwest grounded 115 Boeing 737-800 aircraft Wednesday evening after discovering discrepancies between weight data sent to its dispatch team and other weight records.
"Out of an abundance of caution, we temporarily ceased flying the respective aircraft to enter the correct weights of the aircraft in question into the system and reset the program," spokesman Chris Mainz said. "As of Thursday morning, we are making steady progress resolving the discrepancy tail by tail, and we have returned roughly half of the aircraft and counting back into service."
The weight discrepancies were 75 pounds.
The groundings accounted for more than a fifth of the approximately 500 aircraft Southwest has in its active fleet. The carrier also has approximately 250 planes parked due to Covid-19 and the 737 Max grounding.
This isn't Southwest's first recent issue with weight discrepancies. In January, the FAA proposed a $3.92 million fine against Southwest for allegedly operating aircraft with incorrect calculations of weight and balance data between May and August of 2018.
The carrier operated 44 aircraft on a total of 21,505 flights with incorrect operational empty weights and center of gravity data during that period, the FAA said. Such information is used in determining how many passengers and how much fuel can be carried aboard aircraft as well as where cargo must be located.
Southwest said at the time that the issue had resulted in it implementing additional controls for managing aircraft weight data in its computer systems.
Mainz said Wednesday's grounding will cause some delays and cancellations, though the impacts should be minimal. Southwest had delayed 197 flights, 9% of its Thursday operations, as of early afternoon eastern time, according to Flight Aware. The carrier had canceled 14 flights.