January 7, 2004 (by Stefaan Vanhastel) - The Air Force has found quite a few defective engine parts in F-16s and has made repairs and ordered extra inspections of the aircraft to avoid future crashes.
Since June, at least 44 faulty turbine blades have been discovered in F-16 engines at Luke Air Force Base. Likewise, during inspections of about 90 F-16s in the Arizona Air National Guard's 162nd Fighter Wing, 10 similar cases have turned up.
The blades recently found to be flawed are relatively new. Ironically, they were installed since the late 1990s in a bid to correct earlier blade defects that caused several crashes in Arizona and elsewhere.
The Air Force ordered the latest service-wide engine inspections after a Luke F-16 crashed about 12 miles northwest of Gila Bend on June 10. That crash was blamed on a faulty turbine blade that broke loose and destroyed the jet's engine, investigators found.
Officials at Luke say the flawed blades have already been replaced, and the jet engines are being electronically inspected for microscopic blade cracks about once a month.
"We're very confident that we've got our arms around this," said Maj. Jodi Unsinger of the Oklahoma City Air Logistics Center at Tinker Air Force Base, which is responsible for most of the Air Force's aircraft engines. "We certainly feel as if things are under control," she said.
That's pretty much what Air Force officials said in the 1990s, when a similar inspection program was put in place to catch cracks in the old turbine blades causing crashes at that time. But that inspection effort was far from foolproof.
At first, the Air Force inspected the suspect engines after every 50 hours of operation at high temperature. As problems continued, the inspection rate was upped to once every 10 hours. But by 1999 some F-16 engines were failing as early as five hours after their last inspections.
The Air Force eventually ordered testing after every five hours and carried out a maintenance program aimed at fixing the problems.
In the last six months, the Air Force has tested more than 2,000 F-16s and F-15s with the suspect engines. A total of 324 faulty turbine blades, including the 44 at Luke and the 10 at Tucson, have been identified so far.
According to a December report in the Air Force Times, engine problems with F-16 and F-15 fighters are "widespread," and "affect 45 percent of the service's 1,380 F-16 Fighting Falcons and 80 percent of the 740 F-15 Eagles."
The fourth-stage, low-pressure turbines have been "suspect" for some time, Col. John P. Harris, commander of the AFB
Maintenance Group said, "but there was nothing certain" until the June 10 crash.
All of Luke's F-16s were grounded for "a couple of days in July until we had a better sense of the risks entailed in operating them," he said.
Once that risks were established, Luke began inspecting its F-16 turbine blades about 15 times per night utilizing an "eddy current" process that uses electrical currents to identify flaws, cracks or other imperfections or impurities in the blades.
"The bulk of the 44 failures occurred very early in the inspections, and it's been between 10 days and two weeks since we failed the last one," Harris said. "It's very rare now. As we weed the bad ones out of the system, there are fewer suspect blades to discover. We'll probably continue to find them periodically, but right now, finding one is rare."
The Air Force blames the problem on a manufacturing defect in Pratt and Whitney's F100-PW-100, -200 and -220 engines.
Pratt and Whitney spokeswoman Laurie Tardif said the problem stems from "a subtle manufacturing defect" in Pratt and Whitney's F100-PW-100, -200 and -220 engines, a flaw the company has traced to one of its suppliers.
"That defect has been identified and the corrective action is in place", Tardif said. "Pratt and Whitney is helping to inspect the fighter engines and replaces blades as needed."