Southwest extends 737 MAX flight cancellations through early August

By David Shepardson

WASHINGTON (Reuters) - Southwest Airlines on Thursday extended its cancellation of 737 MAX flights through early August as the grounding of the Boeing Co jet continued and threatened to impact nearly all of the busy U.S. summer travel season.

Southwest, the largest operator of 737 MAX airplanes worldwide, said it would now keep the aircraft off its flight schedule until Aug. 10, instead of through June 6.

The revision will remove roughly 371 weekday flights from its total peak-day schedule of more than 4,000 daily flights, which is about 10% higher than the 330 weekly flights it said were being cut through June 6.

American Airlines Group Inc and United Airlines Co have both canceled flights into June. The last round of cancellations was made before Boeing announced it was pushing back its estimate of when the planes would return to service to mid-year.

Boeing said on Thursday it was standing by that "present mid-2020 estimate for return to service." The MAX has been grounded worldwide since March after two fatal crashes killed 346 people.

Shares of Boeing and Southwest were flat on Thursday

The Federal Aviation Administration declined to comment.

Separately, a series of unresolved issues threaten to push back a key certification test flight until April or later, a person briefed on the matter said.

One remaining issue is whether Boeing will need to separate two bundles of wiring on the plane that may be too close together, which could lead to a short circuit and crash if pilots do not respond appropriately.

The topic has been under discussion by the FAA and Boeing for more than a month and it is unclear how soon it may be resolved. A spokeswoman for the European Union Aviation Safety Agency said on Thursday it has made no recommendation and is "waiting for additional information from Boeing."

Last week, Boeing said it was continuing to "perform the appropriate analysis" but it was unclear when that "will lead to any design changes."

Boeing and FAA are also reviewing two software issues. One involves a power-up monitoring function that verifies some system monitors are operating correctly.

The other relates to an indicator light associated with the stabilizer trim system that incorrectly illuminated in the flight deck during testing.

FAA Administrator Stephen Dickson told reporters in Singapore this week, "the certification flight is the next major milestone and once that is completed I think we will have a good bit more clarity on where the process goes forward."

(Reporting by Ankit Ajmera in Bengaluru and David Shepardson in Washington; Editing by Bernadette Baum and Matthew Lewis)