F-18 fighters aboard the aircraft USS Enterprise have been called in to backfill in Afghanistan after all non-mission critical F-15 flights were temporarily suspended Saturday following the crash of an older model during a routine training session in Missouri last week.

According to Air Force officials, the cockpit broke apart from the plane's fuselage in mid-flight on Friday. The pilot ejected safely. An investigation into the cause of the accident is still ongoing.

All F-15s, including those used for routine air to ground combat missions over Afghanistan, are grounded until further notice, and the Enterprise, the Navy's lone Persian Gulf carrier, has been ordered to move to the northern Arabian Sea.

This move is a routine method for providing relief to pilots and aircraft flying in that region, according to Navy Spokesman Captain Tom Van Leunen.

The Air Force has 676 F-15 aircraft available in it's fleet and on average these planes are 15.5 years old. The oldest models range in age from 24-29 years.

If the investigation finds that structural problems led to the accident, all 676 aircraft will be inspected. One Air Force official said it's an unlikely possibility that F-15s will be grounded permanently but it does highlight the overall concern about an aging fleet.

The Air Force has been struggling to free up funds to purchase more advanced aircraft such as the stealth F-22 Raptor, one the most advanced aircraft available, to replace these older planes. Attempts to create funds in recent months involved drawing down forces by 40,000 airmen, an effort that Air Force Secretary Michael Wynn has said "isn't working."

The competition in the air may soon be getting stronger. China has increased its military budget by about 17.8 percent to about $45 billion this year, and Air Force officials here say China is working to match technology of our F-22. Currently the Air Force has only 97 F-22s available for use.