Defense Technology International - January/February 2008 - (Page 54) INSIGHT EDITORIAL T he U.S. Air Force announced on Jan. 9 a return-to-flight plan for F-15C/ D fighters, grounded in the aftermath of a Nov. 2 mishap, in which an F-15C that was delivered when Jimmy Carter was president, and its pilot was 10, disassembled itself over rural Missouri. The announcement cleared 260 jets to start flying but left 180 requiring repairs. I spent most of a day over the Christmas break at the Seattle Museum of Flight on the edge of Boeing Field. One wing of the museum is the Red Barn, Boeing’s first factory, set up to show how planes were built in the 1920s. Old Soldiers Fade Away Beside one handcrafted wood-andmetal fuselage skeleton is a 1920s design handbook, which notes that the most important parts of the structure are not the transverse frames but the longerons that extend along the fuselage and do the same job as the keel of a boat. Longerons were what broke over Missouri, which is why the return to flight of the F-15s is good news only in a “thank God, the executioners didn’t have bullets” sense. The reason structures fail is that the information wasn’t good enough and the fatigue model didn’t reflect real-world loads. As the structure gets older, this gets progressively more likely. Lifetime is a projection multiplied by a safety factor, and errors in the projection will only accumulate over time. Modifications to the structure induce more uncertainties. Both factors are present in the F-15 force. The Eagles are outside any previous experience of fighter lifetimes. First, the F-15 was the first fighter capable of 9g sustained turns, and its power and wing loading lead to more dynamic flight profiles than older fighters saw. Second, the current force is older than any fighter force in history: Plans to replace all the C/Ds with F-22s were abandoned a decade ago. At the same time, investigators are looking at fixes that have been applied over time to the fighter’s aft fuselage. These may have made the rear fuselage sti er—in one of these “I-cannot-alterthe-laws-of-physics” consequences, this changes the stresses on the rest of the fuselage. It’s not hard to get the uneasy feeling that the Missouri accident could be one of 54 DEFENSE TECHNOLOGY INTERNATIONAL JANUARY/FEBRUARY 2008 those structural failures—like the crash of a 48,000-hr. 707 freighter at Lusaka, Zambia, in 1977—that makes people realize we don’t know all the answers. Any early, enforced retirements are going to put more stress on the rest of USAF’s fighter force. The generals have been complaining about this for so long that a lot of people have developed compassion fatigue—but maybe a visual image might help. The scene is a coalition flight-line in Nowhere-istan, 2014. Here is a line-up of Royal Air Force and Luftwaffe Typhoons, under eight years old. The same goes for those French Rafales and a joint force of Swedish and South African C/D Gripens. Over there is a flight of 10-yearold, armed-to-the-teeth Indian air force Su-30s, alongside a half-dozen UAE air force F-16Fs and some brand new Singaporean F-15SG Eagles. On the U.S. side of the airfield, the only relatively youthful jets are a few F-22s— the operation has limited use for pure air-to-air fighters—and a Navy/Marine contingent of Super Hornets, whose pilots get tired of telling their partners that they have closed their airbrakes, thank you. Of the USAF F-16s and F-15Es, only a handful are less than 20 years old, and many of them are close to the age of the jet that was lost in Missouri. If there are F-15C/D aircraft there, most are thirty-somethings. Any real rejuvenation of the force won’t start for another two years, when the F-35A enters fullrate production. This is not a warning. It’s the result of plans that were set in motion in the mid-1990s, when the Clinton administration bet the future on the Joint Strike Fighter. Cutbacks in the F-22 program, and delays in upgrades that would make it more versatile, have been another turn of the screw; it is only the Navy’s dogged pursuit of the Super Hornet Block 2 that has given that service a plan B. USAF leaders are going to be watching as the F-15s emerge from this standdown, as engineers use the lessons learned to take a fresh look at the F-16 and F-15E force, and as the F-35A heads toward flight testing. They will be nervous, and for good reason. I —Bill Sweetman Read Sweetman’s posts on DTI’s weblog, Ares, updated daily: aresblog.net www.aviationweek.com/dti http://aresblog.net http://www.aviationweek.com/dti
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.