The U.S. Air Force has directed that all F-15 fighter jet models A-D be grounded after a recent investigation showed they need additional inspections.

Following the crash of an F-15 earlier this month in a wooded area 120 miles southwest of St. Louis, the jets were grounded while Air Combat Command investigated. Designed in the 1970s, the jets are most commonly used for air-to-surface combat in Afghanistan.

The fleet-wide problems include cracked rails that hold the aircraft fuselages together, according to Air Combat Command. This grounding will be in effect until all necessary repairs are completed.

The grounding stems from an incident on Nov. 2, when an F-15 fighter jet broke apart during a training mission while the aircraft was in flight over Missouri. Investigators are still trying to conclude what caused that incident, but the most recent grounding follows revelations that the jet’s upper longerons, the metal framing that holds together the cockpit and the fuselage, was damaged.

Investigators are now planning to inspect all F-15 A through D models for similar structural deficiencies.