Air Force Leaders Discuss F-15 Accident, Future (Source: US Air Force; issued Jan. 10, 2008) 
While 260 US Air Force F-15A to –D fighters have returned to flight, over 40% of the fleet have faulty parts and may not fly again. (US Air Force photo)WASHINGTON --- Senior Air Force leaders gathered for a press conference here Jan. 10 to share findings from the accident investigation board currently examining the Nov. 2 crash of a Missouri Air National Guard F-15C Eagle.
The upper right longeron -- one of four metal beams that help hold the cockpit to the main fuselage -- was found to have manufacturing defects, said Col. William Wignall, the head of the accident investigation.
The one longeron, already not up to design specifications, cracked apart under the stress of a 7G turn, the colonel said. This led to the other longerons failing as well, which then caused the cockpit to separate from the rest of the fuselage. The pilot was able to eject, but suffered a broken arm when the canopy snapped off.
The incident led to the grounding of the Air Force's F-15 fleet. As of Jan. 9, the Air Force approved 60 percent of F-15 A through D models to return to service with no flight restrictions.
"We've had great involvement from Boeing during the investigation," Colonel Wignall said. "In fact, they're the ones who determined the longeron was the problem. This was then confirmed by the Air Force Research Laboratory."
During the fleet's grounding, every F-15 base conducted a series of detailed inspections. During that timeframe, nine other F-15s have been found to have similar cracks in their longerons.
The difficulty is that issues have been found with F-15s built between 1978 and 1985, across A through D models at several bases, so no one source of the problem can be isolated, said Gen. John D.W. Corley, the commander of Air Combat Command.
"This isn't just about one pilot in one aircraft with one bad part," General Corley said. "I have a fleet that is 100 percent fatigued, and 40 percent of that has bad parts. The long-term future of the F-15 is in question."
In the meantime, F-22 Raptor, F-16 Fighting Falcon and F-15E Strike Eagle pilots have picked up the F-15s usual mission of patrolling and defending American airspace and interests.
That has had a ripple effect among those pilots' missions, General Corley said. "We don't have a full and healthy fleet, so we've gotten behind on training missions, instructor certifications, classes and exercises," he said. "And in the meantime, our pilots have to be ready to deploy."
For some of the nine F-15s that have longeron cracks, it may be cost-prohibited to repair them, General Corley said. The Air Force is scheduled to retire some of these aircraft in the next fiscal year.
"We're going over each and every aircraft to make a determination," he said. "We will take some F-15s out of the inventory. It just doesn't make sense to spend the time and money if it won't be worth it for some aircraft."
The Air Force first began flying the F-15 in 1972 and has 665 F-15s and F-15Es in its inventory. Its replacement, the fifth generation F-22, is currently in production with active squadrons at Langley Air Force Base, Va., and Elmendorf AFB, Alaska. (ends)
Most Air Force F-15s Get Green Light to Fly (Source: US Department of Defense; issued Jan. 10, 2008)
WASHINGTON --- About 60 percent of the Air Force’s F-15 Eagle fighter fleet has been found fit and ready to again defend the skies over the homeland or perform overseas missions, senior U.S. military officers said here today.
About 260 F-15s were returned to full operational duty Jan. 8 after receiving nose-to-tail inspections following the Nov. 2 midair breakup of a Missouri Air National Guard jet as it flew south of St. Louis during a training mission, senior Air Force officers told reporters today at the Pentagon following today’s release of the accident investigation report. Much of the Air Force’s nearly 700 F-15s had been grounded since the incident.
The report cited the failure of a structural component called a longeron as causing the F-15C to break into two parts. Although injured, the pilot was able to successfully eject from the aircraft and parachute safely to earth.
“We are ... lucky that this pilot survived,” said Air Force Gen. John D.W. Corley, commander of Air Combat Command, at Langley Air Force Base, Va. ACC furnishes airpower for stateside defense and overseas military purposes. The F-15 constitutes the backbone of United States’ domestic air defense assets, said Corley, who wears a second hat as air component commander for U.S. Joint Forces Command, at Norfolk, Va.
Technical study of the F-15’s recovered wreckage determined that the component in question did not meet the manufacturer’s structural specifications and had developed cracks that caused it to fail, according to the report.
When the upper-right-hand longeron broke, the remaining structure along the forward fuselage was unable to distribute the loads in that area, which caused the aircraft to break into two at a point just aft of the cockpit area, explained Air Force Col. William Wignall, president of the accident investigation board.
“This is not just a bad part, this is a bad part that’s been under huge stress” for nearly three decades, Corley said. The accumulated fatigue and stress on that part caused it to crack and eventually to break, he said.
F-15 aircraft returned to duty have undergone extensive inspections, said Air Force Maj. Gen. Thomas J. Owen, commander of Warner Robins Air Logistics Center, Air Force Material Command, Robins Air Force Base, Ga. Owen’s unit is responsible for logistics support for various Air Force aircraft, including F-15s.
“No (operational) restrictions will be imposed on the aircraft that have passed the inspections, although future recurring inspections will be required to the upper-right and left longerons,” Owen said.
About 182 F-15 A through D models manufactured between 1978 and 1984 remain out of service pending additional tests, officials said. Nine other F-15s have been found to have longeron-fatigue cracks and have been grounded. About 441 F-15s in the Air Force inventory are model A through D, while 224 others are of the newer E series.
Inspections performed on the F-15 fleet are more than 90 percent complete. They include thorough checks of hydraulic and electrical lines, fasteners, aircraft fuselages and skins, and all internal structural components, including the longerons, Owen explained.
Air Force Material Command and its partners in industry “remain committed to the defense of our nation and the safety of the men and women who operate the F-15 aircraft throughout the world,” Owen said. (ends)
F-15 Eagle Accident Report Released (Source: US Air Force; issued Jan. 10, 2008)
LANGLEY AIR FORCE BASE, Va. --- A failure of the upper right longeron, a critical support structure in the F-15C Eagle, caused the crash of a Missouri Air National Guard F-15C, four miles south-southeast of Boss, Missouri, Nov 2.
According to the Air Combat Command Accident Investigation Board report released Jan. 10, a technical analysis of the recovered F-15C wreckage determined that the longeron didn't meet blueprint specifications. This defect led to a series of fatigue cracks in the right upper longeron. These cracks expanded under life cycle stress, causing the longeron to fail, which initiated a catastrophic failure of the remaining support structures and led to the aircraft breaking apart in flight.
The pilot received injuries to his left shoulder and arm prior to ejecting from the aircraft. The $41.7 million aircraft, assigned to the Missouri Air National Guard's 131st Fighter Wing, was destroyed on impact. There were no fatalities. The pilot was the only person aboard the single-seat F-15C. The crash caused minimal damage to private property.
The board president, Col. William Wignall, a senior F-15 pilot, noted the pilot's actions during the mishap sequence were focused, precise and appropriate. The pilot's actions did not contribute to the mishap, said Colonel Wignall. In addition, a thorough review of local maintenance procedures revealed no problems or adverse trends which could have contributed to the accident.
To download the report's executive summary, statement of facts and statement of opinion, visit:
http://www.acc.af.mil/aibreports/.
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