Singapore is “in the advanced stages of evaluating the F-35,” according to its air force chief. The U.S. has been asking other partner countries on the Lightning II to commit to a block buy. But that prospect has now receded for a couple of years, after the latest report on the stealth fighter by the Pentagon’s own weapons tester, released on February 1.

The Director, Operational Test and Evaluation (DOT&E) listed a range of deficiencies in the Block 2B software that was loaded on the U.S. Marine Corps F-35Bs when they declared initial operational capability (IOC) last July. He also described problems with the Block 3i version with which the U.S. Air Force wants to declare IOC on the F-35A next August. And the development and test schedule for the ultimate Block 3F software was judged “unrealistic.”

In the U.S. system, the services can declare IOC before the DOT&E conducts a formal IOT&E (Initial Operational Test and Evaluation). The IOT&E for the F-35 is supposed to start in August 2017, upon completion of the jet’s System Development and Demonstration (SDD) phase. But in his latest report, the DOT&E warned the U.S. and its F-35 partners against committing to a block buy before the IOT&E is done.

“Significant discoveries requiring correction…[and] will continue to occur throughout the remaining developmental and operational testing,” he noted. All the aircraft delivered to date need modifying before they are combat-ready, he added. Lockheed Martin and the F-35 Joint Program Office (JPO) began calling for a block buy last year in order to drive down unit costs to the $80 million goal for the F-35A version.

The JPO said there were no surprises in the latest DOT&E report, which had not given enough credit for the program’s efforts to solve problems that arose. Recent technical challenges that had been successfully overcome included the F135 engine rub, the F-35B auxiliary inlet door, and the F-35C tailhook. “Risks do still exist but are understood and manageable,” it added.

At a briefing in Washington last week, JPO chief Lt Gen Chris Bogdan said there were currently 419 deficiencies in the program that needed correction, but another 700-plus had already been addressed. He said that the proposed block buy would not now take place until U.S. Fiscal Years 2019 through 2021, although it had the potential to save the U.S. and international F-35 partners over $2 billion in savings.

In the meantime, the JPO is in the final stages of negotiating Low Rate Initial Production (LRIP) batches 9 and 10 with Lockheed Martin and engine maker Pratt & Whitney.

More than 150 F-35s are now operational, and together with the 18 SDD aircraft, they have logged more than 48,000 hours. Five partner nations–Australia, Italy, the Netherlands, Norway and the UK–are now flying the jet. Israel and Japan will receive their first examples this year. Training of pilots and maintainers is progressing well, the JPO said. It listed eight significant achievements in 2015, including 90 flight test separations of seven weapons–the DOT&E report noted the “limited weapons carriage, i.e. two bombs, two air-to-air missiles,” of the Marines’ F-35B at IOC.

The JPO conceded that much work remained to be done on the mission systems software. The DOT&E said that Block 2B suffered from “deficiencies in fusion” and “ambiguous threat displays.” Block 3i was supposed to re-house Block 2B onto new core processors without modification, but the U.S. Air Force has “insisted on fixes for five of the most severe deficiencies.” Flight testing of the definitive Block 3F software began last March but probably can’t be completed before January 2018, the DOT&E believes. It also describes a separate and serious set of problems relating to compilation of the mission data files.

The DOT&E report also mentioned the flight-testing of the F-35’s ‘dog-fighting’ capability, the report of which was leaked last July. This subject has been controversial for years–and some say the jet represents a new warfighting regime in which close air combat capability is irrelevant. Anyway, 17 engagements were staged between an F-35A and an F-16D that was restricted to 7g by carrying fuel tanks. Nevertheless, the F-35A “remained at a distinct disadvantage on every engagement,” the DOT&E reported.

The DOT&E noted problems with the ejection seat (see Box 1); over-pressurization of the wing fuel tanks (a fix is under review); and the structural life of the F-35B bulkhead (see Box 2). A host of other issues were identified in the 50-page report but the JPO pleaded for these to be taken in context. It is during development that “issues are expected to be discovered and solutions are implemented,” it said. Development is now 80 percent complete, the JPO added.

Some Other Points from the DOT&E Report

- Despite the fielding of version 2, many critical deficiencies remain in the Autonomic Logistics Information System (ALIS), and its cybersecurity has not yet been properly tested.

- Test pilots are reporting positively on the Generation III helmet-mounted display system (HMDS). This is designed to solve the problems of jitter, latency and ‘green glow’ that afflicted the previous Gen II design.

High-fidelity simulation of the full range of threats and scenarios is not likely to be available to the IOT&E team, which will mean more actual flights being needed.

-Fleet availability in 2015 averaged 51 percent versus a goal of 60 percent, and hardly improved over 2014. The numbers are depressed by the F-35B version.

-The Marines’ suitability demonstration of six F-35Bs on the USS Wasp last May suffered from poor reliability and required extensive contractor logistics support.

-There are heat build-up problems in the weapons bays.

-Live-fire and EMP vulnerability testing is as expected.

-All three variants are meeting their empty weight goals–but only just for the F-35C.

The Ejection Problem

The DOT&E report provides more detail on this safety issue that has emerged. Lighter-weight manikins wearing the new and slightly heavier Gen III HMDS, that were ejected at 160 knots during sled tests last July and August, revealed neck injuries. As a result, pilots weighing less than 136lbs are currently banned from flying the F-35.

Martin Baker’s design of the jet’s US16E seat included a trio of airbags that inflate in a two-stage process during ejection as head and neck restraints. The company has now designed and sled-tested a fabric mesh support panel that fits behind the pilot’s head and between the parachute risers. It seems to work, but more testing is required and the mod could take a year to install on the fleet.

In addition, a ‘heavy/light’ switch has been designed. When in the light(weight) position, the switch delays extraction of the ejection seat parachute by milliseconds, which should further reduce shock and stress on the pilot’s neck. – C.P.

Structural Life Testing

Earlier this month, BAE Systems reported that the structural design life of the F-35–8,000 hours–had been tested twice over on an F-35A test airframe in the company’s facility at Brough in the UK. The 350-tonne test rig there includes more than 160 loading actuators, 2,500 strain gauges and 20 miles of wiring. Having ‘flown’ 16,000 hours, the airframe will now be subjected to a third lifetime of testing, before being dismantled for analysis.

But it’s the F-35B STOVL version which has proved more problematic, with a wing carry-through bulkhead severing in 2013 after 9,080 hours. This caused a redesign and a 16-month delay before structural testing resumed. There were some more discoveries in 2015, leading to another five-month pause. Meanwhile, cracks were discovered in the front wing spars of the F-35C structural test airframe last October, after 13,731 hours. The cause has not yet been defined. – C.P.