by Tech. Sgt. Jefferson Thompson
173rd Fighter Wing Public Affairs
3/25/2015 - KINGSLEY FIELD, Ore. -- Airmen
at the 173rd Fighter Wing here pioneered a critical fix Feb. 26
preserving airworthiness for the Air Force F-15C Eagle aircraft as the
airframes approach 40 years in service.
Master Sgt. Dusty McAllister, supervisor of the 173rd Sheet Metals shop,
asked one of his Airman, Tech. Sgt. Jeff Childs, who has a background
in machining, if it were possible to engineer an inspection point for
wing spars, which are inaccessible at field locations.
This inspection was in response to stress testing conducted by Boeing in
which an airframe was subjected to stresses proportionate to more than
20-thousand flight hours. Those tests revealed a vulnerability in some
"There was a catastrophic failure on the stress test aircraft on the
intermediate spar," said McAllister. "[The engineers] said they need to
find out if we can remove some skin in an area and check these, and we
said, 'yes, we will take a look at this.'"
McAllister, Childs and other members of the shop spent several weeks of
trial and error and created a fixture machined from a block of aluminum
that holds a carbide cutting tool and allows them to cut through the
titanium skin precisely enough to preserve the spar it touches.
"We take off thin layers in successive cuts until we get close, then we
hold our breath for the last cut," said Childs, the one who physically
performs all the cutting operations.
The operation has worked well enough that he visited the wing's sister
unit, the 142nd Fighter Wing in Portland, and showed them how to make
the fixture and helped them cut five wings.
McAllister says that depot maintenance thinks the design is excellent
and is sending it to all F-15 units to help them accomplish their
"A rough drawing of the fixture and a new [Time Compliance Technical
Order] has gone out to all the F-15 units to begin working the fix,"
He adds that they continue to refine the process and are looking at
using an ultrasound scan to help measure the thickness between cuts to
provide a wider margin of error.