Sun Country Airlines is bracing for cost headwinds in the fourth quarter (Q4) due to a high number of its aircraft undergoing heavy airframe maintenance checks.

During the third quarter (Q3) Sun Country’s adjusted unit costs, which exclude fuel, increased 2.6% year-over-year to 7.75 cents. The company’s CFO Dave Davis said the timing of maintenance events was a large contributor to the airline’s cost increase in the quarter.

The airline expects its heavy check volume to remain high in Q4 relative to the same period in 2022, Davis said. The number of heavy checks planned for Sun Country’s aircraft during Q4 is roughly three times the level of Q4 2022.

Sun Country’s elevated levels of heavy checks is “probably a four-to-five-million-dollar issue for us in Q4,” the airline’s CFO said. At the end of Q3, the airline had 42 aircraft in passenger service, 12 freighter aircraft, and five held for operating lease. Minneapolis-based Sun Country operates Boeing 737-800s.

Due to a lack of available captains, Sun Country flew approximately 3,500 fewer block hours in Q3, mostly in July, the airline’s CEO Jude Bricker said. He said if those block hours were operated, they would have produced “somewhere in the range of seven to $10 million dollars of operating earnings for the quarter.”

As Sun Country’s growth has moderated due to pilot staffing, the airline has opted to lease two aircraft that were scheduled to join its fleet in Q4. The entry into service for those two 737-800s is now planned for the first quarter of 2025.

The company’s staffing challenges are not stemming from pilot hiring or attrition, but Captain upgrades, Davis said. “We are seeing positive trends based on some of the actions we’ve taken over the last six months,” he added.

Despite the Captain upgrade challenges and maintenance expense, Sun Country posted a Q3 net profit of $7.6 million, down from its $10.7 million net profit in Q3 2022. Its total revenue grew by 12.3% year-over-year to $248.9 million and expenses increased 11.4% to $229.9 million. The airline’s Q3 maintenance costs increased 39% year-over-year to $15.3 million.