The US military has grounded all but “mission critical” aircraft after two fatal mid-air accidents recently.
The “no-fly” order announced on Friday comes a day after two Apache helicopters collided in Alaska, killing three American pilots.
Army Chief of Staff James McConville said the pilots would remain on the ground until they completed additional training.
The crash of two Black Hawk helicopters in Kentucky on March 20 killed nine soldiers.
“We are deeply saddened by those we lost,” General McConville said in a statement.
“It is their loss that makes it even more important to review our safety procedures and training protocols, and ensure that we train and operate at the highest levels of safety and efficiency.”
He added that Army pilots “will focus on safety and training protocols to ensure that our pilots and crews have the knowledge, training and awareness necessary to safely complete their mission.”
The resignation is effective immediately. It does not affect any other part of the US military except the Army.
Active duty troops will have to complete their training within 24 hours of the first week of May, while National Guard and Reserve units have until the end of the month.
Since each unit has reported completing training, they will be able to resume normal activities.
Recent events are being investigated in various parts of the country, but officials say there is “no indication of any direction.”
The military said the incident occurred Thursday near Fort Wainwright, Alaska, as troops were returning from a training mission. In addition to the three dead, one was seriously injured.
Three soldiers were part of the 11th Airborne Division, called the “Arctic Angels,” according to the Associated Press.