By JOHN SEEWER, Associated Press

The Trump administration is promising to fix the nationwide shortage of air traffic controllers after recent control tower mishaps and a string of crashes earlier this year.

The need for more controllers who direct planes across increasingly crowded skies, though, isn’t a new issue or one that will be resolved quickly.

How big is the shortage of controllers?

The Federal Aviation Administration has about 14,000 air traffic controllers. More than 1,800 were hired last year, the largest number in nearly a decade, and the government is on track to hire even more this year. Still, there’s a need for about 3,000 more to fully staff the system.

What are the impacts?

Understaffing has meant controllers often are forced to work mandatory overtime, sometimes six days a week. That has led to concerns about fatigue after highly publicized close calls between planes that were following orders from controllers. The FAA agreed last summer to increase the minimum rest time between shifts. In some high-traffic areas, including New York and Florida, the FAA has limited the number of flights because of the lack of controllers.

Why is there a shortage if thousands are being hired?

It’s a demanding and stressful job with unpredictable hours and a high turnover rate. Many don’t make it though the first few years. And experienced controllers face a mandatory retirement age of 56.

Is this just a recent concern?

The National Air Traffic Controllers Association has been raising concerns for more than decade, telling Congress in 2015 that the shortage was at a crisis level. It said then that the FAA had missed its hiring targets for five years in a row. The union again said last spring that the number of fully certified controllers was down 10% from where it was 10 years ago.

What’s the Trump administration’s plan?

The administration wants to “supercharge” the controller workforce and announced a program last week to speed up hiring and give existing controllers more money not to retire early. But because it takes years to train and certify new hires, Transportation Secretary Sean Duffy said it still will take at least three or four years to meet the current needs.

How do you become a controller?

Most go through several months training at the FAA Academy in Oklahoma, although about one-third of the candidates don’t make it to the end. Others are taught the job in the military, and a handful of colleges offer the same training found at the academy. Trainees then go on to work as developmental controllers in airport towers or radar centers until they’re ready to be certified. That final step typically takes two to three years.

What are the requirements?

The FAA says trainees must be willing to go anywhere across the U.S. while working nights and weekends. Applicants must be a U.S. citizen, younger than 31 and able to pass a medical exam, background check and a skills assessment. The FAA says less than 10% of applicants are accepted into the training program.