A program to train Afghan attack pilots has been ended after the airmen kept going absent without leave, or AWOL, while training in the United States.

More than 40 percent of the Afghan Air Force students enrolled in the U.S.-based training program to fly the AC-208 Combat Caravan, a light attack combat aircraft, went AWOL, according to a quarterly report by the Special Inspector General for Afghanistan Reconstruction, or SIGAR.

The training took place at Fort Worth, Texas, SIGAR told Air Force Times. Northrop Grumman operates a 5,000 square-foot custom-built classroom space located at Meacham Airport in Fort Worth.

“The AC-208 Training Center of Excellence is designed to provide partner nations with instructional classroom activities and initial aircrew and maintenance training on the Northrop Grumman modified AC-208 Eliminator aircraft,” a Northrop Grumman press release reads.

Those students that did not go AWOL were pulled back to Afghanistan to complete their training. As a result, only one class graduated from the U.S.-based program. The second and third classes will continue and finish their training in Afghanistan.

SIGAR said they did not have data on whether the AWOL pilots were recovered. U.S. Immigration and Customs Enforcement did not immediately respond to a request for comment.

However, the phenomenon is neither new, nor limited to Afghan Air Force trainees.

“We found that nearly half of all foreign military trainees that went AWOL while training in the United States since 2005 were from Afghanistan (152 of 320),” SIGAR reported in October 2017. “Of the 152 AWOL Afghan trainees, 83 either fled the United States after going AWOL or remain unaccounted for.”

× Fear of missing out? Sign up for the Air Force Times Daily News Roundup to receive the top Air Force stories every afternoon. Thanks for signing up. By giving us your email, you are opting in to the Air Force Times Daily News Roundup.

NATO’s Resolute Support mission in Afghanistan maintains a cohort of advisers to train Afghan airmen known as Train Advise Assist Command – Air, or TAAC-Air.

TAAC-Air told the inspector general that it has a plan to continue the student training and is developing a contract solution to support the effort to train the initial group of AC-208 aircrew.

Afghan pilots are a common target for Taliban hitmen, who know taking out highly-qualified attack pilots has a major impact on the battlefield.

In this 2016 photo, two Afghan pilots walk past a C-208 plane at the Afghan military airbase in Kabul, Afghanistan. (AP Photo/Rahmat Gul)

It is not uncommon for Afghans to go AWOL while training in the U.S., with many claiming asylum after being apprehended. Those asylum claims are sometimes approved, as was the case of an Afghan officer who slipped away from a U.S. training exercise in Massachusetts, according to the Associated Press.

The first female Afghan pilot was also granted asylum after she continuously received death threats, according to the Wall Street Journal.

The Afghan Air Force has had some notable success in the past year, as A-29 attack pilots began flying night-time raids and dropping laser-guided bombs in combat without coalition advisers assisting them.

However, the operational success is tempered by shortfalls on the maintenance side of the mission. The Afghans still rely on contractor support for maintaining aircraft, and the number of Afghan airmen trained to provide airmen is consistently below authorized manpower levels.

U.S. contractors who provide maintenance assistance will not be able to stay in country to continue their work if U.S. troops are no longer in place to provide security, the Pentagon inspector general has warned in the past.

In the case of some airframes, such as UH-60 Black Hawks, Afghan pilots are not trained and qualified at a fast enough rate to keep pace with deliveries of the aircraft.

Although the Mi-17 fleet forms the backbone of the Afghan Air Force, the U.S. government plans to supply 159 UH-60 Black Hawks to Afghanistan by 2024.