Fire Down Below

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I’m sure that the spin experts are even now writing their reviews of the latest report on the F-35 program by Michael Gilmore, the Pentagon’s director of operational test and evaluation. And to save you some time, here are some of their comments:

- The “testing bureaucracy” always wants more testing, to keep its members in work.
- The DOT&E’s job is to take the glass-half-empty view; for the sake of balance, read the Lockheed Martin release.
- The report is about last year, and all the trends are positive for better performance in 2013 and beyond.

However, the awkward fact is that the DOT&E has been reporting on the F-35 program since its inception, and has been critical of the progress of the flight test program since the early days of flying, and (unless I have missed something) nobody has pointed to an example where their reports erred on the negative side. Which is not something that can be said for the JSF's supporters.

Indeed, they score a told-you-so point concerning their warning three years ago that the removal of check valves from fluid lines – which automatically stop the flow if the line is damaged downstream – would make the aircraft more vulnerable to hostile fire. That was before the start of live-fire testing at China Lake.

Now, testing has shown that the polyalphaolefin (PAO, related to synthetic motor oil) coolant in the avionics system poses a fire risk.“The threat in this ballistic test ruptured the PAO pressure line in the area just below the cockpit, causing a sustained PAO-based fire with a leak rate of 2.2 gallons per minute.” In engineering language: “a similar event in flight would likely cause an immediate incapacitation and loss of the pilot and aircraft.”

A fix for that problem is not impossible, although difficult: most check systems are triggered by higher leak rates, so designing a valve that shuts off below a catastrophic fire level, but that does not result in high false-alarm rates, is tricky.

Some of the issues identified are going to present more problems – and indeed, in some areas the program office has given up and accepted lower performance. Sustained g and transonic (Mach 0.8 to 1.2) acceleration specifications have been relaxed for all three variants – indicative of less-than-expected specific excess power, most likely due to higher drag.

The F-35C’s transonic acceleration has changed dramatically, increasing by 43 seconds compared to a 65-second threshold requirement (which was not exciting in itself – many fighters can do the same in half the time). Operationally, one impact of this change is on the time at supersonic speed available in any given mission profile: a long, full-power transonic acceleration burns a lot of fuel.

The F-35B has a full-page litany of mechanical problems with the powered-lift system, including a couple of issues –  redesigning the driveshaft, and a new clutch material – which have large lifetime and maintainability impacts and for which solutions are still in the design stage. No show-stoppers, but not the sort of thing that points to a low-maintenance system in service.

All versions are still restricted in maximum Mach number at altitude because of exhaust heat damage to coatings and structures on the horizontal tail surfaces, a problem that surfaced in 2011.

On the other hand, it might be argued that the above issues can all be solved easily before the aircraft enters service – because the critical item there has nothing to do with stealth coatings, aerodynamics or coolant. It’s software, and this is where the DOT&E report may be of most concern.

Software releases, the report says, ran late – and that is against the schedule adopted after the 2010 technical baseline review, which was carried out in part to correct optimistic projections made before that date. (The program’s leaders had underestimated the amount of regression testing – tests to make sure that changes had not induced problems in previously tested functions – and overestimated test rates and productivity.) Block 1 software is not complete. Lot 2 and Lot 3 aircraft have been delivered “with major variances against the expected capabilities”.

Block 2A, the initial training software, was four months late and less than half of it was available at the point where the report was written. Block 2B, intended to be the first combat-capable software, is late. Block 3i (interim), a bridge between 2B and the service-standard Block 3F, “has lagged in integration and laboratory testing.”

Software problems are part but not all of the reason for slow progress with weapons integration, along with optimistic and inaccurate assumptions about the need for margins and the availability of instrumentation and range support. “The impact of these delays will potentially require an additional 18 months added to the schedule for weapons integration events,” the report warns.

The report adds to the uncertainty surrounding the F-35’s initial operational capability dates. Last summer, Congress added language to the 2013 budget that called on the USAF and Navy to name IOC dates for all three versions by year-end – then changed the deadline to June 1 at the last minute. The most recent Selected Acquisition Report disclosed that Block 3F initial operational test and evaluation, a necessary event for IOC, would not be finished until 2019 – and that does not include any additional weapons integration time.

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