The Air Force said it has grounded its fleet of F-15 fighters, including those providing air defense for Hawai'i, because of airworthiness concerns following a training crash last week in Missouri.

The 199th Fighter Squadron of the Hawai'i Air National Guard has 18 of the twin-tail fighters.

There are more than 700 F-15 Eagles in the Air Force inventory, but the planes are no longer made. The aircraft, which reached initial operational capability in 1975, patrolled no-fly zones in Iraq and flew in operations Provide Comfort in Turkey, Allied Force in Bosnia, Enduring Freedom in Afghan-istan and Iraqi Freedom.

The cause of Friday's accident is under investigation, but the Air Force said preliminary findings indicate a structural failure of the aircraft may have occurred.

A 10-year veteran of the Missouri Air National Guard, whose name was not released, ejected from an F-15C when it crashed in rural Dent County, Mo., on private property surrounded by national forest. The pilot suffered a dislocated shoulder, a broken arm and minor cuts.

The single-seat plane, a 1980 model worth $40 million, was assigned to the 131st Fighter Wing at Lambert-St. Louis International Airport.

In June, an F-15 from the Oregon Air National Guard crashed in the Pacific Ocean on a training mission. In the same month, one of the jets crashed near Eielson Air Force Base in Alaska. And in May, an F-15 went down in southwestern Indiana during training.

The Air Force said it grounded the entire fleet on Saturday as a safety precaution based on the Friday crash.

F-15s are based on the Mainland and in Alaska, Britain, Hawai'i, Japan and the Middle East. Combat requirements in Iraq or Afghanistan will be met by other aircraft during the interim such as the F-16, A-10 and B-1B, the Air Force said.

Capt. Jeff Hickam, a spokes-man for the Hawai'i National Guard, said the 199th Fighter Squadron is approaching a record 80,000 hours of accident-free flying in the F-15.

Brig. Gen. Peter S. Pawling, the commander of the Air Guard's 154th Wing, said it's too early to tell what kind of impact the grounding will have because officials don't know how long it is expected to last.

But the training that occurs throughout the week over O'ahu has been curtailed.

Maj. Gen. Robert G.F. Lee, the state adjutant general and head of the Hawai'i National Guard, said the F-15s remain ready to fly in the event of an emergency.

"We are continuing to man those aircraft with our alert crews, although there are no training flights," Lee said. "The skies are a little quieter until we figure out what we might have to check additionally."

Hickam said there has never been an aerial F-15 accident involving the 199th Fighter Squadron. Around the late 1960s, a Hawai'i Guard F-4 Phantom pilot did have to eject because of a fuel problem, he said.

The 63-foot-long F-15s, which can fly faster than 1,875 mph, or Mach 2.5 plus, were deployed to Iraq in 2000 for no-fly-zone duty and patrolled the skies above Honolulu after the 9/11 attacks.

The aircraft will be replaced by F-22A Raptors with stealth technology starting in late 2011.

Reach William Cole at wcole@honoluluadvertiser.com.