Boeing delivered 33 airplanes in September, six more than during the same period a year earlier, as the company and its customers keep an eye on the impact of a machinist strike, now in its fourth week.

Through September, Boeing has handed over 291 aircraft, well below the 371 it had delivered in the first nine months of 2023. Rival Airbus has delivered 447 airplanes this year through August,

Last month’s deliveries were led by 27 of Boeing’s bestselling 737 Max aircraft to customers including United Airlines, which received five, and Ryanair and Southwest Airlines, which each each took three. Deliveries are key to Boeing. It’s already burned through more than $8 billion this year since customers pay the bulk of the price when they receive the airplane.

The aircraft are produced in Renton, Washington, one of the factories where machinists walked off the job on Sept. 13 after workers overwhelmingly voted down a tentative agreement the company had reached with their union. The two sides are back at the negotiating table this week, though the union dismissed a sweetened offer from Boeing last month.

All but 10 of the 27 Maxes were handed over before the strike began, according to Jefferies aerospace analyst Sheila Kahyaoglu. In a note Monday, she forecast that Boeing will be producing 25 Max aircraft per month if the strike ends in October but the company’s planned ramp-up to 38 Maxes a month will be delayed by a year.

Boeing is scheduled to report quarterly results on Oct. 23, when it will detail the financial impact of the strike.

September deliveries also included four 787 Dreamliner planes, which are made in Boeing’s nonunion factory in South Carolina. For the month, Boeing logged 66 gross orders for new aircraft.

Boeing has spent much of this year dealing with fallout after a near catastrophe on one of its new 737 Max 9s in January, when a door plug that was missing key bolts blew out.

The company’s backlog is 5,456 aircraft.