Washington, Nov 7, SPA -- The U.S. Air Force has grounded all of its F-15 fighter jets after an accident in Missouri triggered concerns about the aging fleet, officials said Tuesday. The decision came after Japan on Sunday grounded its F-15 fleet after it was informed by U.S. forces that an Air National Guard F-15 jet had crashed.“The cause of that accident is still under investigation,” the U.S. Air Force said in a statement. “Preliminary findings indicate that a possible structural failure of the aircraft may have occurred. The suspension of flight operations is a precautionary measure.”The Air Force has more than 700 F-15s in its fleet. For now, however, they can only be used for emergency missions in Iraq or Afghanistan, while newer F-16s will be used for all routine operations.“They have some concerns about structural issues with the F-15 that went down,” said Pentagon spokesman Bryan Whitman. “The Air Force is looking at its operational requirements and where they have the newer aircraft, and we are making some of those available for missions while they take a look at the F-15 and see if they have a more systemic problem throughout the fleet.”The airplane that crashed on Friday was a 27-year-old F-15C. About 500 of the total F-15 fleet are older models with an average age of 25 years. There also are about 223 of the later F-15E models, which are mostly the ones used in Iraq. The Air Force is trying to replace its oldest F-15s with the F-22 Raptor made by Lockheed Martin, but due to budgetary constraints, it has so far only been able to purchase half of the aircraft it has requested. The U.S. Congress has given approval for the Air Force to buy 183 F-22s, although military officials have said they need 381 of the aircraft. A total of 97 F-22s already have been integrated into the fleet.--SPA www.spa.gov.sa/497567