Hercules Crash In Baghdad Points To Metal Fatigue In C130's Wing Center

Air Safety Week,  Feb 21, 2005  

• E-mail
• Print
• Link

"Whirl-Mode" Phenomenon May Also Be At Play

When a Royal Air Force (RAF) Hercules crashed about 19 miles northwest of Baghdad on Jan. 30, the natural assumption was that it had been brought down by enemy action. The brass weren't so sure because it had spun down from an altitude that should have been above the range of a shoulder-fired missile. An opportunistic insurgent group released via al Jazeera a hastily cobbled-together video of flaming wreckage and a non-MANPADS (man-portable air defense system) missile being fired.

But that fraud quickly fizzled and the mystery deepened. Had a sapper or insurgent managed to place a device aboard? It seemed unlikely given where the aircraft had been and the security there. The inflight "explosion" had torn the right wing off near the root at medium altitude in the cruise, the right wing being found some considerable distance from the main wreckage. A senior RAF spokesman said, "sabotage is a distinct possibility but even though metal fatigue is another option, it's considered much less likely."

Less than two weeks later, the U.S. Air Force (USAF) announced that it was grounding 30 of its C130Es and placing another 60 C130Hs on restricted flight status. Some of the grounded aircraft were operating in Iraq, Afghanistan and Kuwait. The USAF's Air Mobility Command (AMC) had been monitoring cracks in the planes' wing box structure since 2001, but evidently the grounding decision hadn't been premeditated -- but was comparatively sudden. Inspections of the aircraft in the past four years have revealed that cracks "were greater in number and severity than originally expected," the AMC spokesman at Robins Air Force Base, Lt. Dustin Hart, said. Replacing the older planes with new J models is "one of the options," Hart said. Accordingly, on Feb. 10, Gen. John Jumper, the Air Force chief of staff, told U.S. senators the service was rethinking its plan to end purchases of C130Js, and he dismissed criticism of their performance, according to Reuters news service. The Pentagon has admitted that two other C130 crashes had been attributed to metal fatigue.

Stuff Of Legends Cracking

Air forces the world over would find it hard to do without the workhorse C130. Its presence in war zones and on humanitarian relief missions is stuff of legends. But the immediate reflexive response from the UK Ministry of Defense (MoD) was that RAF C130s would not be grounded, as they are similar "but not identical" models. The RAF C130K is indeed very similar to the E model, yet the distinctions have more to do with perceptions of fatigue as related to age than reality, according to some ex-RAF pilots. The RAF's C130K, they say, is nothing more than a 1968-70 E model but with Dash 15 engines (as fitted to the later H model). Supposedly, the center wing-boxes are fabricated from the same type and strength of aluminum (as the C130E). The "K" model only designated UK specified avionics, i.e., it wasn't a bona fide Lockheed model designation.

Unlike the C130E, the UK's K model had no explosion suppressant foam in its tanks (which helps limit internal wing flexing to some extent). Most of the older RAF C130s were given new center-sections in the mid 70s to mid 80s at Marshalls of Cambridge, and the outer wings were rebuilt with new planks top and bottom. This was done specifically to address the fatigue problems with the older type wing. However, it has been the fatigue spectrum accumulated since the mid 80s that has aged the RAF fleet inordinately, particularly over the last five years. Over that same period, USAF Depot Level Maintenance revisit time was extended from a three-year cycle to a five-year cycle. Each airframe would take four to six months to refurbish. It was mostly at these teardowns that the picture of cumulative fatigue damage was realized.

Refocusing On The Metal

UK investigators are now focusing on metal fatigue because no evidence has been found of enemy action. An MoD source said: "It's hard to believe that there might be a structural failure after all the close monitoring we do, but there is a history of surprises about metal fatigue." British investigators are now examining evidence from a U.S. crash in 2002 in which metal fatigue caused a wing to break off in mid-air. The UK MoD has now taken the highly unusual step of calling in the civilian Air Accidents Investigation Branch (AAIB) to help find the cause of the crash of its 1965-built C130, number XV179, one of the six oldest in RAF service. In a Feb. 12 release, the RAF emphasized that the C130 "has an excellent safety record" and that its Hercules Fleet is "routinely and continuously monitored for metal fatigue." An MoD spokesman said that the investigation had reached no conclusions and that "if the president of the board of inquiry had had any concerns, he would have already grounded the fleet. ... If the U.S. thought there was a problem, they would have informed us."