Structural Flaws Hamper a Host of Military Aircraft

Air Safety Week, Jan 7, 2008

Some U.S. Navy P-3C Orion anti-submarine warfare (ASW) turboprops have joined over 400 U.S. Air Force F-15 Eagle fighters on the ground because of concerns over structural flaws. The U.S. military aircraft grounding orders remain in place as the UK Defence Ministry and the Royal Air Force (RAF) offer abject apologies for the September 2006 crash of a Nimrod MR2 surveillance aircraft in Afghanistan.

Nearly a fourth of the USN's fleet of Lockheed Martin P-3C Orions have been grounded due to fears of structural fatigue. The Navy said 39 of the 161 operational P-3Cs are affected, with repairs expected to take 18-24 months per plane.

The Navy issued an Air Frame Bulletin on Dec. 17 after "program officials determined that these aircraft are beyond known structural limits on the lower section of the P-3 wing. The concerns are the result of continuing P-3 fatigue life analysis and validation by physical findings," the Naval Air Systems Command said in a written statement.

"The Navy's goal is to ensure that its aircrews operate aircraft that are structurally sound and safe for operational flight. In the interest of safety, the grounded aircraft will either return to safe operation after replacement of critical structural components or will be removed from service," the statement continued.

A NAVAIR spokesman said the grounding order did not result from a crash, but was rather prompted by continuing engineering analysis started in December 2004 to anticipate components' growing risk to failure.

The Navy had expected to fly most of its P-3Cs through 2019. The Orions are to be replaced by 108 Boeing P-8A Poseidons, a derivative of Boeing's Next Generation 737-800.

P-8A production started a month ago. Initial operating capability is scheduled for 2013 with full operational capability planned for 2019. The Poseidon is the first Navy aircraft to be produced on an existing commercial production line.

Meanwhile, Air Force maintenance personnel continue to perform methodical and time-intensive inspections on all Boeing F-15A/B/C/D Eagle fighters in the wake of the F-15 grounding order issued on December. 3.

The F-15 stand-down follows additional information received from the ongoing investigation of a Nov. 2 F-15C mishap, which resulted in the loss of that aircraft. The Missouri Air National Guard Eagle was on a training mission. The aircraft crashed in a wooded rural area after the pilot ejected.

The USAF Accident Investigation Board (AIB) that was convened found serious defects that indicate potential structural damage in the rest of the fleet, but the official crash investigation has yet to be completed.

Throughout the Air Force, maintainers have found cracks in the upper longerons of eight F-15s (as of Jan. 2). Four of these aircraft are assigned to the Air National Guard's 173rd Fighter Wing, Kingsley Field, OR; two are assigned to the 18th Wing, Kadena Air Base, Japan; another is assigned to the 325th Fighter Wing, Tyndall AFB, FL; and one assigned to the ANG 131st Fighter Wing, St. Louis, MO.

Every USAF F-15---on average 25 years old---will undergo all previously published time compliance technical order inspections. However, unlike in recent weeks, the cleared aircraft will not immediately return to flight. Technical experts at Warner Robins Air Logistics Center, GA, are developing new inspection techniques based on findings in parts of the mishap aircraft. These inspections will be performed as soon as the new inspection techniques are available for the affected F-15s.

Maintenance crews are working around the clock worldwide stripping paint and performing non-destructive inspections in the F-15's upper longeron just aft of the canopies.

The F-15s require inspection times of between 12.5 hours and 20 hours. The B and D models are more time consuming because they have two seats. The rear seat requires removal to access the upper longerons.

Inspections involved more than just a visual check. After the paint is stripped and bare metal is exposed, airmen from the non-destructive inspection shop apply chemicals that reveal cracks under a black light. Other inspections in hard-to-see areas are done with a bore scope - a tool that uses a tiny camera and fits in tight areas.

Pieces of the crashed jet were retrieved and sent to the Air Force Research Lab to see what may have caused the aircraft to disintegrate. That information is going to engineers who will determine how to inspect, what will be inspected and the form in which it's done.

Despite the Air Force-wide stand down, F-15 Eagles pilots are maintaining their skills and capabilities through additional time in flight simulators. "The primary simulator training that we do does not differ from the training we do day-to-day when the F-15s are flying," said Capt. Matthew French, a pilot with the 67th Fighter Squadron. "We normally use the simulators to augment our daily training."

Greatly affected by the F-15 grounding order is the 173rd Fighter Wing based at Kingsley Field, Klamath Falls, OR. The unit in south central Oregon, located about 20 miles north of the California border, has seen all 25 of its F- 15C/Ds grounded. The 173rd FW is a training unit for F-15 pilots. Its 20 or so full-time instructor pilots offer basic (B course) and transition (TX course) instruction to other USAF pilots. On any given day, 12-17 student pilots are learning to fly the F-15 Eagle.