After seven months of flighttestus interruptus caused first by an electrical problem and then by the failure and subsequent requalification of the F135 engine, the first Joint Strike Fighter -- aircraft AA-1 -- is back in the air.

Next week will see another milestone as BF-1, the first short take-off, vertical landing (STOVL) F-35B, rolls out in preparation for hover-pit tests -- where the powered-lift system is run up as the aircraft stands on a grating over a deep trench.

BF-1 will be much more important than AA-1 next year. AA-1 itself was built to the pre-2004, overweight JSF design and is not fully representative of the production JSF; and the STOVL version is the long pole in the tent, because it needs more flight testing than either the F-35A or the Navy F-35C, and is supposed to enter service first, achieving IOC in early 2012.

BF-1 is due to fly in May 2008 and is expected to be flying in STOVL mode by the end of the year. Program vice-president Tom Burbage, talking at a conference in Oslo last week, says that the customer wants a test program in which the jet "backs in" to STOVL -- slowing down from conventional flight to progressively lower speeds in each sortie, finally reaching the hover -- rather than performing "push-up" tests from the hover pit as the X-35B test aircraft did in 2000.

Everyone in the JSF program will be watching the hover-pit tests, though. A key issue: as reported here and here, the jet (to say the least) has no thrust to spare in vertical-flight mode. So far, says Burbage, recent rig tests of the F135 and its lift fan are showing that thrust is higher than expected. (That was the experience in the X-plane program, where the jet popped up to 30 feet on the first push-up, to the consternation of the engineers.)

The team is not taking credit for the lift bump, but it will be a big relief if it's still there on the hover pit. At the same time, work is underway on a redesigned second stage for the lift fan, which optimizes the work split between the two counter-rotating stages and provides another vertical thrust boost.

What Burbage calls "constipation" in the production system is also a concern, because the front-loaded test program needs to get assets on time. The problem centers on the big main frames or bulkheads that hold the wings and body together: early frames were late and the effect is rippling through the line.

On the sales side, Burbage is in constant motion, still trying to set up a deal between multiple non-US customers and the US government to reduce early-aircraft prices. The issue is that export customers -- particularly Australia and the European F-16 founder nations -- need early deliveries from the low-rate initial production (LRIP) batches, but that these come with a scary price tag.

That's a cost of doing business for the US government, which plans to buy many, many more aircraft once production stabilizes, and buys year-by-year by law; but export customers who are ready to sign multi-year contracts see it as a raw deal.

Read more Av Week predictions about the JSF's 2008 fortunes at Military.com.

-- Christian