The Air Force has made considerable progress whittling down the massive maintainer shortfall that it once feared was threatening the service’s aircraft readiness.

Air Force officials said that at the end of fiscal 2017, the service was short about 400 maintainers. That’s 10 percent of the roughly 4,000-maintainer shortfall the Air Force reported at the end of fiscal 2015.

By the end of fiscal 2016, the Air Force said it was about 3,400 maintainers short.

But there’s still a lot of work to be done to get the maintenance ranks back up to full strength. Air Force spokeswoman Laura McAndrews said it will be five to seven years before the newly hired maintainers are fully seasoned and experienced.

“We are continuously evaluating opportunities to improve our readiness as quickly and effectively as possible,” McAndrews said.

McAndrews said the Air Force used several growth and retention tools to help close the maintenance gap. It brought on an additional 2,000 new maintenance trainees in 2017, on top of the 6,000 it usually accesses each year, and it expects to also increase accessions by 1,000 over the usual level in fiscal 2018.

The Air Force also approved high year of tenure extensions to hold on to some maintainers, offered selective re-enlistment bonuses, and started using direct duty prior service accessions to let some maintainers who had left the service back in, McAndrews said.

McAndrews said that several events over the past decade — particularly the 2014 force management drawdown, sequestration and other budget cuts — “have created severe turbulence in aircraft maintenance manning” and led to the shortfall.

Squadrons facing shortages of crew chiefs, avionics airmen, and other maintainers often wind up with the remaining maintainers working long hours and on weekends. The Air Force fears that if things don’t turn around, more and more maintainers will get sick of the pace of work and leave the service for good, making it even tougher for the service to keep crucial planes in the air.