Stealth Fighter’s Crash Reveals a Design’s Limits

Maybe the U.S. Stealth fighter that crashed during NATO strikes over Yugoslavia suffered mechanical failure. Maybe it was hit by Serbian air defenses that just got lucky. Maybe it went down because of pilot error.

But what if the F-117A Nighthawk crashed because the Serbs penetrated the jet’s stealth, or radar-evading, design technology?

That’s a chilling scenario for many, because the U.S. government has spent more than $50 billion to build not only the F-117A but two other Stealth aircraft: the B-2 bomber, which is also being used in Yugoslavia, and the next-generation F-22 fighter jets due to be operational early in the next century.

If the Yugoslavs, with their 1960s ground-to-air missile system, could shoot down an F-117A, that would mean that the F-117A’s stealth design is starting to show its age, some analysts said. But the F-117A’s technology dates back to the 1970s, while the stealth technology used on the B-2 and F-22 is far more advanced, they noted.

“What should probably surprise is that our monopoly on stealth has lasted so long,” said Andrew Krepinevich, executive director of the Center for Strategic and Budgetary Assessments, a think tank in Washington. “This monopoly has lasted arguably since the early ‘80s. So it’s a matter of time.”

Unlike prior F-117A missions, in the Persian Gulf and in Panama, the strikes in Yugoslavia forced the aircraft to fly in ways that may have compromised its stealth characteristics, making it vulnerable to radar-guided missiles, Lockheed experts said in interviews Monday. Even though the aircraft is aging and its designers knew one would be lost during combat eventually, the first such casualty left them wounded.

To be sure, neither the Pentagon nor Lockheed Martin Corp., which developed the F-117A and then built 59 of the $45-million planes, has yet said why the jet crashed. Its pilot was later rescued.

An investigation is ongoing, and “we want to be very careful in pulling together as much information as we can about how it happened,” Pentagon spokesman Kenneth H. Bacon told reporters Monday.

Bacon said the F-117A is “still an integral part” of the North Atlantic Treaty Organization strategy in Yugoslavia. But he acknowledged that “we obviously have concerns about [the F-117A’s] vulnerability,” in terms not only of technology but of flight tactics, attack routes and other factors.

Lee Whitney, a spokesman at Lockheed Martin’s Bethesda, Md., headquarters, declined comment, as did officials at the company’s Palmdale facility.

But to engineers familiar with stealth technology, one look at the triangle-shaped aircraft speaks volumes about how far science has come since the F-117A first took to the air. The reason its body is made up of flat surfaces, for example, is that the 1970s computers used to design it couldn’t perform calculations to measure the radar resistance of three-dimensional objects.

Not Acknowledged to Exist for 7 Years

The Pentagon didn’t even acknowledge the F-117A’s existence until 1988, even though the fighter first flew in 1981 and entered active service soon after. The aircraft was developed and built in Burbank at Lockheed Martin’s famed top-secret Skunk Works plant, which was later relocated to Palmdale.

Despite the F-117A’s age, it remains the world’s most advanced operational combat jet and flew more than 1,200 sorties during the 1991 Persian Gulf War without a single craft’s being damaged by Iraqi fire.

That feat amazed even the Lockheed Martin engineers who conceived the aircraft. After all, their brainchild was flying through a daily haze of antiaircraft gunfire. One factor in the F-117A’s favor in the Gulf War was the terrain: flat, open deserts similar to the New Mexico and Nevada territory where its pilots trained.

Yugoslavia, by contrast, is marked by rugged hills where targets are more easily concealed. Such terrain is likely to force F-117A pilots to make quick turns--maneuvers that vastly increase the aircraft’s profile for radar trackers. Even a standard banking maneuver increases the aircraft’s radar profile by a hundredfold, sources said.

Alan Brown, the retired chief engineer of the F-117A design program, said the news that one had been shot down came “like a knife through the stomach,” but he said he doesn’t believe the Yugoslav forces have found a way to negate the plane’s stealth characteristics.

“I didn’t think the bottom had dropped out of the technology,” said Brown, now a consultant to Lockheed Martin, adding, “You just know that, one day, they’re going to have to get one.”

Even if the Yugoslav forces simply lucked out in their attack on the aircraft, analysts suggested they have raised the odds in their favor by clustering their radar installations along likely NATO flight routes. Bunching the radar stations together increases their power.

Experts discounted the notion that Yugoslav President Slobodan Milosevic’s forces have devised a technology to simply beat the F-117A’s radar invisibility.

“If the Yugoslavs have done it, it’s probably the military story of the century,” Krepinevich said. “Based on one incident, I think it’s premature to say stealth has been compromised.”

Stealthy, Yes, but Not Invulnerable

But analysts also said that the Pentagon and Lockheed Martin have never maintained that the stealthy design and materials of the aircraft made the planes incapable of being hit.

“They have never claimed that stealth was perfectly invisible, only that it makes it much less visible than a normal airplane,” said Lawrence Korb, director of studies at the Council on Foreign Relations, a New York think tank.

“You’re going to get some shot down, but you’re not going to get as many shot down as in the ‘50s and ‘60s,” he said.

Also, the F-117A uses an early generation of stealth technology. The stealth features on the B-2, built by Northrop Grumman Corp. in Palmdale, and on the F-22 from Lockheed Martin and Boeing Co. are far more advanced.

In fact, Saturday’s crash of the F-117A “may be an argument in favor of the F-22 because it does have a more advanced form of stealth,” said Daniel Goure, deputy director for political-military studies at the Center for Strategic and International Studies in Washington.

Goure said it’s unlikely the F-117A crashed because of mechanical failure, because “if that was the case, I would have expected the Pentagon to have said something by now. It would have been very reassuring to people worried about stealth’s effectiveness.”

But an “operating problem” could be the culprit, Goure said. The jet “is not equally stealthy in all conditions, for instance when it opens a bomb bay” and when it flies at low altitude, he said.

The F-117A also has had a reputation as a difficult plane to fly. At least two crashed while the aircraft was still a top-secret project in the 1980s. Another crashed during an air show in the suburbs of Baltimore in 1997.

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Sometimes Invisible, Sometimes Not

The F-117A Stealth aircraft is often referred to as a fighter but is basically a bomber that uses special non-reflective coating and design features to avoid enemy radar. It isn’t entirely invisible, however. When the bomb doors open, it will show up big and bright on enemy radar screens. And during the 1991 Persian Gulf War, British radar operators claimed that the F-117As were detectable on Britain’s older radar, which uses a long wavelength.

Stealthy but slow

Cost: $45 million

Number remaining: 56

Length: 66 feet

Wingspan: 43 feet

Speed: Subsonic

Height: 12 feet

Weight (fully loaded): 65, 800 lbs.

Range: Unlimited with air refueling

Date deployed:1982

Builder: Lockheed Martin Corp.

When It’s Vulnerable

By overlapping radar sites, Serbian radar operators can spot incoming planes at one site, then fire and track missiles at another.

1. Pilot levels out plane for optimal release of its two bombs.

2. When bomb bays open, the projecting doors give the F-117A a radar profile visible to enemy antiaircraft positions.

3. Pilot attempts to release bombs before enemy radar can lock on, then quickly closes bay.

4. Shoulder-carried missile launchers can also target F117A, but its infrared image is hard to read.

Sources: Jane’s How to Fly and Fight in the F-117A Stealth Fighter, Adm. Eugene Carroll, Associated Press, Times staff reports; researched by CHRIS ERSKINE and REBECCA PERRY/Los Angeles Times