WASHINGTON -- Ever since a U.S. Air Force F-117 was downed over Yugoslavia on March 27, Pentagon officials have puzzled over what could have brought down one of the world's stealthiest warplanes.
Two weeks later, after extensive interviews with the pilot, a review of technical clues and an analysis of how the Serbian air defenses have been operating, a secret Air Force inquiry now believes a combination of tactics, quick learning and luck came together in one brilliant moment to shoot down the premier attack jet in America's arsenal.The culprit, they believe, is an SA-3 surface-to-air missile. But it probably was not used in the normal fashion, with its operators relying only on their own local radars to detect the target.
Instead, Air Force and other military officials now believe that Serbian spotters in Serbia, and perhaps in Bosnia and along the Montenegrin coast, may have patched together enough quick glimpses of the warplane from scattered radars to track the elusive aircraft, however briefly, to fire a missile from a battery near Belgrade.
The Serbs used their radar sparingly in order to avoid a counterattack by the NATO fighter.
For the Serbs, it was a longshot, low-tech solution to a challenge posed by one of the most sophisticated warplanes in the world, Pentagon officials said. In the end, it may have been tactics aided by a lot of luck, and not technology, that brought down the F-117 and gave Belgrade a propaganda windfall.
"We think whoever did this won the lotto that night," said one senior American officer.
NATO and Pentagon officials have such respect for Yugoslavia's air defenses that low-flying attack planes have flown only a handful of strike missions. But shooting down an F-117 showed unusual skill. In addition to its radar-absorbing skin and radar-scattering angles, the Nighthawk, as the F-117 is called, typically flies a zig-zag pattern to avoid tracking.
The F-117 is not invisible, but barely visible to most radars. It is most vulnerable when turning suddenly at low altitudes, which can reflect radar beams to receivers, or when opening its bomb bay door.
What American military officials now suspect is that Serbian spotters, perhaps starting with spies in Italy watching the F-117s take off, were able to determine a rough schedule of how long it took the planes to cross the Adriatic, and how long to fly to Belgrade.
Knowing this, Serbian radar operators would have a better sense of when and where to watch. Once a shadowy figure crossed their screens, they would alert the operator down the line. The downed F-117 had already dropped at least one of its laser-guided, 2,000-pound bombs near Belgrade, so that was another clue.
Analysts are unsure now whether Serbian gunners were able to integrate this net of far-flung radars to feed the location of the plane to a missile launcher, or to cue up the SA-3s own radar so the operator had only to briefly flip it on to track and fire.
Since the stealth plane went down, other planes on bombing runs have recorded instances when the Serbian forces lobbed surface-to-air missiles at them without radar guidance. This is clearly less reliable, but it lets the Serbian missile sites avoid counterstrikes by NATO's fighters, whose own missiles can home in on the beams of Serbian ground radars.
"Given the limited air space over there and the sophisticated air defense system they have," the senior American officer said, "there's always the possibility of a kill."
Officially, the Pentagon says the cause of what downed the plane is still under investigation. But military officials familiar with the inquiry say this account is emerging as the most likely explanation of what caused the first-ever F-117 lost in combat, and the only manned aircraft felled so far in the aerial bombardment of Yugoslavia.