GRAHAM WARWICK / WASHINGTON DC
But with only one aircraft dedicated to clearing the flight envelope, testing has been slower than anticipated
After a slow start, Lockheed Martin/Boeing F-22 Raptor avionics flight testing is gathering pace. But the stealthy fighter is likely to enter US Air Force operational evaluation next year with significant limitations because of delays in clearing the flight envelope.
The eighth F-22 has flown and will join the test fleet at Edwards AFB, California, later this month, while the ninth and final development aircraft is on the flight line at Lockheed Martin's Marietta, Georgia, plant. "Testing is actually going quite well, now we are finally getting avionics aircraft out there," says Brig Gen Jay Jabour, USAF F-22 system programme director.
While there will soon be six aircraft involved in avionics testing, there is only one dedicated to clearing the flight envelope. "The long pole in the tent is the structural test," says Jabour. "We are limited to one aircraft, 4003, and testing has gone slower than anticipated. We are three months behind schedule." Testing is under way in the 7g+ regime. If initial operational test and evaluation (IOT&E) begins as scheduled in April next year, it will not be with the full envelope. "We have got to get to IOT&E with an envelope we can use. The air force is looking at how much envelope is needed," he adds.
There is "significant risk" in holding to the April 2003 date for the start of operational evaluation, says Jabour. "But there is no hard-and-fast reason for that date. It is driven by funding." IOT&E could be delayed, and the programme would still meet the schedule for a full-rate production decision, while initial operational capability (IOC) is still planned for December 2005.
There are no "show stoppers" in avionics testing, according to Jabour. The Northrop Grumman APG-77 active-array radar "has been a real success", he says, exceeding performance and reliability expectations. The second live firing of a Raytheon AIM-120 Advanced Medium-Range Air-to-Air Missile (AMRAAM), conducted in January, was "fairly difficult", Jabour says, but resulted in the weapon, which lacked a warhead, hitting the subscale target drone. To save time, most AMRAAM "shots" will involve an instrumented test vehicle which will remain in the weapon bay and simulate the missile fly-out.
Avionics flight testing involves Block 3.0 software, which provides radar, communication/navigation/ identification and electronic-warfare sensor fusion. Aircraft 4006 has been grounded for hardware modifications in preparation for the 3.1 software load, which brings in the intra-flight datalink and embedded training. Block 3.0 is performing well, but there are "stability issues", says Jabour. "When it runs, it runs well," he adds, but on some flights the software can recycle "two or three times". Stability enhancements have been incorporated into the 3.1.0 load.
Two more software releases are planned before IOT&E begins: 3.1.1 will allow training of operational testers to begin, scheduled for the third quarter; while 3.1.2, the software load planned for operational evaluation, will add more training, diagnostics and defensive electronic countermeasures. Definition of the Block 4 release for IOC and beyond is being finalised, Jabour says.
Source: Flight International
