The supply of freighter aircraft continues to expand to record levels even as the air cargo market decelerates, raising questions about whether leasing companies and cargo operators are creating more capacity than can profitably exist once shipping growth returns to normal. Analysts say there are more all-cargo aircraft in active service than ever, but their utilization rates are starting to recede from last year’s peak. As the global economy slows and cargo rates drop, older aircraft that were kept in service when capacity was at a premium could quickly be mothballed. “There is going to be a lot more impetus...