A rebound in airline passenger travel is colliding with global supply chain troubles. Airlines are increasingly hard-pressed to find engines and other spare parts to keep their planes flying, according to The Wall Street Journal, leading to delays and flight cancellations that are complicating carrier attempts to capitalize on resurgent travel demand.

That push by customers to get back in the air has caught aircraft manufacturers off guard, leaving parts makers unable to increase production quickly enough to provide components both for new aircraft and for planes already in service.

The aviation sector strains are one sign of how supply chains have struggled to keep up with quick pivots in demand during the pandemic, adding new financial concerns at businesses as they try to adjust their operations. Responding to market conditions is difficult because parts shortages have left aircraft idled for longer periods in heavy maintenance checks.