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Cracks in wing hinges sideline 10 Hornets

Ten F/A-18 Hornets have been grounded and 20 others placed on flight restrictions after “fatigue cracks” were found in some wing-panel hinges, a Navy spokesman said Thursday.

The Navy in early November completed the inspections of nearly 480 in-service Hornets from the Navy and Marine Corps fleet, a move directed by an Oct. 23 inspection bulletin.

The inspections were prompted by the discovery in early October of cracks in wing-panel hinges on 15 aircraft. All Navy and Marine Corps Hornets were to be inspected within the next 15 flight hours.

“We are very encouraged by the results and project minimal operational impact,” Navy spokesman Lt. Clay Doss said.

More than half of the Navy and Marine Corps Hornets are past their original service life of 6,000 flight hours.

The inspection focused on the aluminum aileron hinge. The aileron is a wing panel flap at the trailing edge of the wing. Damage to the hinge or the aileron would severely restrict a pilot’s ability to control or land an aircraft.

The Navy and Marine Corps have 112 Hornets on deployment. Two of the deployed aircraft were grounded, including a Navy fighter and a Marine Corps fighter. Doss declined to say where they were deployed.

Eight deployed aircraft were placed on flight restrictions, Doss said. The deployed aircraft will be fixed on the scene using existing supplies and will not need to be transported to a depot.

Individual commanders set the parameters of flight restrictions, which typically impose limits on an aircraft’s speed, altitude or high G-force maneuvers, Doss said.

The aircraft were grounded and restricted as the problems were identified during the two-week inspection period.

The precise cause of the cracks is not clear, Doss added. The cracked hinge was not listed among the 159 “hot spots” previously identified by the Hornet’s service life analysis.

The Navy and Marine Corps have 636 Hornets, models A through D. The two-week inspection covered the roughly 480 Hornets in active use. The other 156 aircraft already were in a depot or otherwise temporarily out of service and will be checked before returning the fleet, Doss said.

The urgent inspection bulletin underscored the Navy’s concerns about the aging Hornet fleet and its capacity to stay in service until its replacement by a next-generation fighter starting in 2015.

“We are still assessing impact on the strike fighter gap,” Doss said. The fighter gap refers to a decade beginning in 2015, when older-model Hornets start retiring faster than new F-35C Lightning II Joint Strike Fighters arrive to replace them. The gap is projected to be its widest — 69 planes — in 2017.

Loren Thompson, a defense consultant with the Lexington Institute, said the latest problems with the Hornet are not surprising, given the planes’ age — 18 years old on average.

“When you go to war, you use them at a higher rate, and they wear out faster. These are not problems we didn’t anticipate — it’s just that they are arriving sooner because we’re riding them harder,” Thompson said.

In 2005, the Navy extended the Hornet’s service life from 6,000 to 8,000 flight hours and is trying to extend them again to 10,000 flight hours. But some Navy officials doubt the second extension is realistic based on a recent analysis, known as “Phase II” of the service-life assessment program.

“Given the Phase II results, the 10,000 [flight-hour] life limit extension is optimistic and will require inspections and modifications to achieve,” Marcia Hart-Wise, spokeswoman for tactical aircraft program at Naval Air Systems Command, said in a written statement.

The planes found to have cracked hinges have flown 5,000 to 7,500 flight hours.

Thompson said the planes may begin to have significant problems around 8,500 flight hours. While the full 10,000 flight hours might be a stretch for the Hornets, “9,000 looks like it might be doable,” he said.

Despite the aging aircraft, the Navy has recorded a drop in Class A mishap rates for the entire F/A-18 fleet. In 2003 and 2004, the rate was four to five mishaps per 100,000 flight hours. That has decreased to 1.3 per 100,000 hours in fiscal 2008, the lowest rate in almost a decade, according to data from the Naval Safety Center.

A Class A mishap is one that causes death, the destruction of an aircraft or more than $1 million in damage.

Flight hours for F/A-18s have remained mostly constant since 2003, Safety Center statistics show.

The cost of maintaining an aircraft usually rises significantly as that aircraft ages.

“Most of the life cycle cost for a fighter aircraft occurs after it leaves the factory — and that ascends progressively as the plane ages,” Thompson said.

“Once the limits begin to be reached, there are all sorts of problems that potentially crop up that makes the readiness of the aircraft suspect. This isn’t just about safety. It’s about the readiness of the airframe and whether you can count on the aircraft in the course of normal operations.”