Southwest Airlines (WN, Dallas Love Field) said on September 16 that it grounded 130 B737-800s - later revising the number to 115 aircraft - over a minor weight discrepancy and for safety's sake.

The low-cost carrier said that the affected aircraft's weight had been entered into the IT system with a 75 pound (34 kilogramme) discrepancy, amounting to less than 0.05% of a B737-800's maximum take-off weight (MTOW). On September 18, it said that around half of the aircraft were already back in service.

"Out of an abundance of caution, we have temporarily ceased flying the respective aircraft to enter the correct weights of the aircraft in question into the system and reset the program," the airline said.

The error does not require any aircraft modifications but only a correction in the computerised fleet management systems. The LCC said that until the fix was implemented, minor operational issues such as cancellations and delays were possible.

According to the ch-aviation fleets advanced module, Southwest Airlines operates 207 B737-800s. Earlier this year, the Federal Aviation Administration (FAA) proposed to fine the airline USD3.92 million for aircraft weight mismanagement.

In a separate development, the airline joined the ranks of carriers that have revised down their winter capacity due to a slower than expected recovery in demand. According to its latest investor update, the LCC is expecting a 40-45% drop in capacity for September and October, and 30-35% for November. Its capacity for August was 27% down compared to 2019.