SEATTLE—Boeing said on Tuesday it would cut its 787 production rate as it works through a new production-related structural defect in its troubled twin-aisle airliner program. The company now forecasts delivering fewer than half of the lingering 100 or so 787s in its inventory this year—instead of the “vast majority” it had expected—as it continues forensic inspections and costly repairs to address quality flaws in the aircraft. Boeing did not disclose a new production rate for the 787 program, but said it would shift temporarily below the current rate of five jets per month. For the year so far, the company has delivered 156 jets of all types, compared with 157 for all of 2020, it said. The latest new issue, first reported by Reuters on Monday, involved gaps where components are joined together in a forward pressure bulkhead, the U.S. Federal Aviation Administration said. The FAA said late on …