Southwest Airlines said Thursday it has removed the grounded Boeing 737 Max from its schedule for another two months during the peak summer travel season and will drop about nine percent of its planned flights as a result.

Southwest said it took the plane out of the schedule through Aug. 10.

It was the latest move by airlines to acknowledge that the plane won’t be ready to fly as soon as they – or Boeing – had expected. Southwest had previously removed the Max from its schedule through June 6.

Southwest was flying 34 Maxes and expected to receive more when the planes were grounded worldwide last March after crashes in Indonesia and Ethiopia killed 346 people. Without the planes, Southwest said it will remove about 371 weekday flights from its schedule of more than 4,000 flights per day.

Dallas-based Southwest is the world’s biggest operator of Boeing 737s, with about 750 in its fleet. Almost all are earlier versions than the Max and don’t have the same flight-control software implicated in the crashes.

Boeing is conducting test flights with the new software but does not expect the Federal Aviation Administration to certify the changes until this summer. Airlines will need more time after that to inspect their planes and train pilots before they fly passengers.

Surveys indicate that many travellers will be reluctant to fly on the Max, at least for a while.