For two years now, the U.S. Air
Force has been replacing the center wing box (the structure that attaches the
wings to the fuselage) for many of its C-130Es. That's because cracks were
discovered in the center wing box in over a hundred of these aircraft.
This was the first long range model of the C-130,
and all were built in the 1960s. The C-130E used two underwing fuel tanks to
get the extra range, and that put more strain on the center wing box. By the
late 1960s, cracks began to show up in the center wing boxes of C-130Es, and
this component was reinforced with stronger materials. But now, the fatigue
cracks have returned in a big way. Now the center wing box has to be replaced,
which costs up to seven million dollars
per aircraft. It's only possible to refurb about 18 C-130Es a year, so it will
take about a dozen years to upgrade the 155 C-130Es that need it.
The C-130Es have, since the 1990s, been transferred
to reserve units, where they fly fewer hours. But after September 11, 2001,
reserve C-130 units suddenly became a lot more active. That put more strain on
these aircraft, and brought on the center wing box fatigue sooner than
expected. Moreover, the need for all the air transport available has made it
impossible to retire the C-130Es just yet. Thus the program to refurb them with
new center wing boxes.