Older Aircraft Subject To Metal Fatigue -- Shock News


Dan Goure of the Lexington Institute has a probing question: "Where are the F-35's critics when the F-16 develops fuselage cracks?"

He does go on a bit, but the gist of his argument is that critics hold the F-16 to less-demanding standards of performance than those they apply to the F-35 program. 

Guilty as charged, I admit.

The standard is different because the affected F-16s have been in front-line service for 20 to 30 years. Aerospace has made great progress over the years in understanding what cyclic strain does to metal structures, but both predictive tools and testing lose fidelity as the years and cycles go by.

The industry has moved to damage-tolerant design, based on the principle that cracks will occur, but that the structure can be designed and managed so that cracks will be found before they cause failure. According to the USAF, this is exactly what happened: the cracks were caught in a routine inspection. 

It has happened before and it will happen again. You can mill an airplane out of solid titanium, but it won't fly very well. 

Failures in testing are different. Goure is right to point out that some failures are to be expected and that is what testing is all about. But to take the still-unsolved June 23 engine fire as an example:  it is unusual and problematic because at this stage, 13 years into engine development, major problems that are not age- and cycle-related have historically been found and fixed. 

The F-35 gets held to higher standards in this and other respects. However, given the fact that its initial operational capability date with the USAF, in a limited configuration, will be 35 years after the F-16's combat debut, and that the program has cost almost $91 billion to date, that's not unreasonable. 

As Goure correctly observes, USAF leaders have warned that the service's fleet is reaching an unprecedented average age. He does not remind his readers that, in the case of fighters, there is a reason for that. Under the plans in place when the USAF stopped buying F-16s, the USAF would have 400 fully operational F-35s by now, with 110 new aircraft arriving every year, and the F-16 force would be on its way to a well earned retirement.

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