WASHINGTON -- Tires that wear out too soon are adding to the troubles facing Lockheed Martin Corp.'s F-35, the Pentagon's costliest weapons system.
Landing-gear tires made by Dunlop Aircraft Tyres for the Marine Corps version of the fighter have "been experiencing an unacceptable wear rate when operating as a conventional aircraft," according to Joe DellaVedova, spokesman for the Defense Department's F-35 program office.
He said the tire, which costs about $1,500 apiece, demonstrates "adequate wear" when the aircraft performs short takeoffs and vertical landings intended for amphibious warfare vessels and improvised runways.
While replacing worn-out tires may pale as a challenge compared with keeping combat-ready software on track, fixing jittery images in the pilot's helmet and reining in rising production costs, it's emblematic of challenges that the Pentagon must resolve to reduce what's now a $1.1 trillion estimate for operating and supporting a planned fleet of 2,443 aircraft for 55 years.
Marine Corps Air Station Beaufort will be home to three combat squadrons and two training squadrons of the F-35B, which will replace the F-18 Hornets currently flown at the base.
Deliveries of the first jets are expected early in 2014; the air station's readiness date to begin the process is Jan. 1, according to Capt. Jordan Cochran, base public affairs officer.
The first training squadron, Marine Fighter Attack Training Squadron 501, will move to Beaufort next summer from Eglin Air Force Base in Florida, squadron commander Lt. Col. David Berke said last month.
The F-35 has a projected price tag of $391.2 billion for development and purchase of the fleet, up 68 percent from the projection in 2001, as measured in current dollars.
The Pentagon is working with Lockheed Martin and Birmingham, Britain-based Dunlop Tyres on a new design for the landing-gear tires that will be introduced next year, DellaVedova said in an emailed statement. In the meantime, Dunlop has provided a tire that's "improved but still unacceptable," he said.
Michael Gilmore, the Defense Department's director of operational test and evaluation, said the Dunlop tires are "wearing more quickly than expected" because of a "poor design," according to a statement from spokeswoman Jennifer Elzea.
John Butters, a spokesman for Dunlop Tyres, said in an emailed statement that the initial tires "are experiencing high wear rates" and the interim model has "better tread wear." The company says on its website that it makes "world class aircraft" tires "and nothing else."
The Marine Corps model of the F-35 "faces a unique and challenging operational environment" demanding a tire "that can operate without damaging the landing surface," Butters said. The F-35B model also is being purchased by Britain and Italy.
Gilmore said that all three versions of the F-35 are falling short of their planned reliability as measured by flying hours between critical failures and failures that stem from contractor issues. The Air Force model is at 65 percent of its planned reliability, the Navy version at 63 percent and the Marine Corps model at 61 percent, Gilmore said.
While lawmakers, the Pentagon's independent testing office and the Government Accountability Office have said the F-35 is making progress on reliability, top Pentagon officials say more needs to be done.
"We're not where we need to be on reliability now, and I think we can do better," Frank Kendall, the Pentagon's undersecretary for acquisition, said at Senate hearing in June. "We're lagging our own goals" by "a significant margin right now," Kendall said.
Laura Siebert, a spokeswoman for Bethesda, Md.-based Lockheed, said in an e-mail that the company is working with suppliers to reduce defects and unreliable parts. She said there's been a 68 percent reduction since 2009 in supplier- caused defects and defect rates are dropping 10 percent per new construction contact.
"The quality performance of the program is comparable to" earlier Air Force jets "at this stage, while setting a trajectory that will support long-term fleet performance expectations and production rate increases," Siebert said.
DellaVedova said that tires made by Michelin & Cie and Goodyear Tire & Rubber Co. for the Air Force and Navy carrier versions, while running down sooner "than originally desired, are currently averaging adequate wear rates."
Military personnel at flight test centers and training locations "discovered that the tires were wearing out too quickly or becoming too thin," Gilmore said.
Goodyear spokesman Scott Baughman said in an e-mailed statement that the company "works closely with its customers to meet tire specifications." Michelin North America spokesman Brian Remsberg said in an e-mailed statement that "we have not received any complaints or requests for tire redesign."