Santa's sleigh cannot fly without its pilot.

With the peak holiday shipping season fast-approaching, global package delivery giant FedEx Corp is paying retirement-age pilots bonuses of $40,000 — and potentially as much as $110,000 — to keep them flying into next year, according to two sources with knowledge of the matter and a contract seen by Reuters.

The bonuses, outlined in the latest pilot contract and previously unreported, reveal that a wave of pilot retirements, global pilot shortages and rising cargo demand fueled by the growth of global e-commerce are straining the world's largest air delivery fleet.

Any problem in maintaining capacity for FedEx, which many economists consider a barometer of U.S. economic strength, disrupts supply chains at a time when they are already being destabilized by international trade tensions.

FedEx and rival United Parcel Service Inc, which is trying to recruit hundreds of pilots this year but is not paying bonuses, play a crucial role in global supply chains from aerospace to retail, particularly during the holidays when average daily delivery volumes can double.

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