– The Air Force faces a crisis of a shortage of hundreds of fighter pilots that’s projected to grow worse, prompting military leaders to ask Congress to increase incentives to stay in the cockpit, military leaders say.

The service branch projects a gap of about 700 fighter pilots by the end of the fiscal year next month and could reach more than 1,000 by fiscal year 2022, Air Force officials say.

“Air superiority is not an American birthright,” Air Force Chief of Staff David Goldfein said. “It’s actually something you have to fight for and maintain.”

Strong demand among commercial airlines, which face their own projected shortages, and high demands on military pilots flying combat missions on multiple deployments have led many aviators to leave ranks, observers say.

“Flying planes is the most coveted job in the Air Force, so the shortfall in pilots tells you two things: Life has become stressful for America’s war­fighters, and there are plenty of opportunities outside the service,” said Loren Thompson, a senior defense analyst with the Virginia-based Lexington Institute.

The Air Force has asked Congress to increase a pilot re-enlistment retention bonus from $25,000 per year for every additional year served to $48,000 annually. The rate has not changed since 1999.

Pilots have typically signed a five-year or nine-year re-enlistment, but the Air Force is exploring more flexible options, Air Force spokesman Maj. Bryan Lewis said in an e-mail. The percentage of fighter pilots who take the bonus has fallen in recent years. In 2014, 50 percent re-enlisted; in 2015, it was 48 percent and this year fell to 34.9 percent, Air Force figures show.

The goal is to better compete with airlines. The highest-paid experienced pilots at major airlines reportedly earn more than $200,000 a year.

To pump up the number of aviators, the Air Force will select two more sites for F-16 pilot training by the end of the year, Secretary of the Air Force Deborah Lee James said. It also will rely on reservists to help fill the gap, Lewis said. The Air Force has a manning requirement of 3,500 fighter pilots.

The Air Force will boost monetary incentives to try to retain more active duty drone pilots, too. The service branch will increase retention bonuses for drone pilots to $35,000 per year, up from $25,000. It’s also relied more on contractors to fly surveillance missions.