| WASHINGTON, July 29
WASHINGTON, July 29 U.S. authorities have
loosened some flight restrictions on Lockheed Martin Corp's
F-35 fighter jets, allowing pilots to fly faster and
take tighter curves, as military officials investigate a massive
engine failure that grounded the entire fleet of warplanes for
over three weeks.
Pilots can now fly at speeds of up to 1.6 Mach, up from 0.9
Mach, and carry out turns with a gravitational load of 3.2 Gs,
up from 3 Gs, a U.S. defense official and other sources familiar
with the program told Reuters on Tuesday.
The changes will allow F-35 test pilots and trainers to
carry out additional maneuvers and flight tests, but it remains
unclear how much of an impact the grounding and restrictions
will have on the program's flight test schedule for the year.
U.S. airworthiness officials are still requiring inspections
of the Pratt & Whitney engines that power the jet every
three hours, but that requirement and other restrictions may be
revised as the investigation winds down, the official said.
The F-35, the world's most expensive weapons project with a
price tag of about $400 billion, was grounded for weeks after an
engine failure and fire that damaged a U.S. Air Force F-35 plane
as it prepared to take off from a Florida air base on June 23.
The incident prevented the jets from making their
international debut at two British air shows this month, and
could compound software development challenges detailed in a
report prepared before the grounding by the Pentagon's chief
arms buyer. A summary of the report was obtained by Reuters.
The report criticized a March 2014 master schedule developed
by Lockheed and forecast delays of up to 14 months in delivery
of certain software still under development, but said it did not
expect those delays to affect the schedule for the Marine Corps
and other services to start using the jets in combat.
The Pentagon's F-35 Joint Program Office (JPO) said it
agreed with eight recommendations made by the Pentagon report to
improve software development, and was implementing the changes.
Joe DellaVedova, F-35 program spokesman, said the program
had delivered 7.4 million lines of software code so far. The
overall program will include 8 million lines of code for the
aircraft, and 15.9 million lines for ground systems such a
computer-based logistics system, he said.
Lockheed spokeswoman Laura Siebert said the company was
working with the Pentagon to assess the impact of the grounding
and flight limitations on the F-35 flight test program.
"The development schedule has margins built in to allow for
discoveries and occurrences like these, and we remain confident
that we will complete 2B software to support Marine Corp
(initial operating capability) in July 2015," she said.
The flight restrictions will be lifted when the root cause
of the incident have been clearly identified, DellaVedova said.
Sylvia Pierson, F-35 spokeswoman at a southern Maryland air
base, said the Marine Corps' F-35 B-model jets and the Navy's
C-model jets were now carrying out five or six flight tests a
Officials have determined that the engine failure occurred
when a component in the third stage fan blade rubbed too hard
against an adjacent seal during a certain flight maneuver,
according to a briefing provided to U.S. lawmakers.
Details about the maneuver were not immediately available. A
second defense official said other jets in the F-35 fleet that
carried out the same maneuver did not exhibit signs of the
"excessive rubbing" seen in the engine that failed.
(Reporting by Andrea Shalal; Editing by Mohammad Zargham)