Ask Hackaday: How Did They Shoot Down a Stealth Aircraft?

It was supposed to be a routine mission for U.S. Air Force Lt. Col. Darrell P. Zelko, a veteran pilot of the 1991 Gulf War. The weather over the capital city of Serbia was stormy on the night of March 27th, 1999, and only a few NATO planes were in the sky to enforce Operation Allied Force. Zelco was to drop 2 laser guided munitions and get back to his base in Italy.

There was no way for him to know that at exactly 8:15pm local time, a young Colonel of the Army of Yugoslavia had done what was thought to be impossible. His men had seen Zelco’s unseeable F117 Stealth Fighter.

Seconds later, a barrage of Soviet 60’s era S-125 surface-to-air missiles were screaming toward him at three times the speed of sound. One hit. Colonel Zelco was forced to eject while his advanced stealth aircraft fell to the ground in a ball of fire. It was the first and only time an F117 had been shot down. He would be rescued a few hours later.

How did they do it? How could a relatively unsophisticated army using outdated soviet technology take down one of the most advanced war planes in the world? A plane that was supposed be invisible to enemy radar? As you can imagine, there are several theories. We’re going deep with the “what-ifs” on this one so join us after the break as we break down and explore them in detail.

Theory 1 – Lucky Shot

The Serbian Army was monitoring US and NATO UHF and VHF communications, which were oddly enough unencrypted. This combined with the fact that the stealth fighters were using the same entry and egress routes means they could have worked out the general area of where they were going to be and when they were going to be there.

Theory 2 – Radar Hack

It has been theorized that they modified the antiquated soviet radars to operate at longer wavelengths. So when the bomb bay doors opened, they could see the aircraft. But using a longer wavelength would have required modification to the radar antenna. Such modifications are not easy to pull off, and would require advanced test equipment and knowledge. Is it possible to do this in the field with no testing or equipment?

invisible man standing in rain

 Theory 3 – The Invisible Man in the Rain

Imagine Harry Potter had donned his invisibility cloak and was making his way out of the castle, when it started raining. Though other wizards and witches might not be able to see Harry directly, they would be able to see a disturbance in the rain. Want to see something invisible? Provide a medium and look for the disturbance within it.

It has been speculated that Colonel Dani tapped into the country’s cell phone network then looked for, found and targeted such a disturbance. But how would they pull this off? Would a stealth fighter, or any plane cause a visible disturbance in the RF field? If so, how do you detect it?

Theory 4 – Your Turn

How would you detect a stealth aircraft?

200 thoughts on “Ask Hackaday: How Did They Shoot Down a Stealth Aircraft?

  1. During war in Croatia it was same with every aircraft who come: Just wait ready with all weapons you have. The strongest weapons was fear and knowledge (weak points). Later in Serbia this F117 was seen with naked eyes and shot down by regular air-defense artillery. Forget stealth, radars, SAM. Missiles was “story for news”.

  2. Bomb bay actuator on this jet was stuck open (mechanical failure) leaving a nice square metal cavity for radar to bounce off and target. That plus the operator in that area later shot down a top F-16 squadron commander in the same area a week later. This radar op was one of there best radar operators and he proved many times before and after racking up hit after hit though he did luck out on the mechanical failure on this one. As it prior air force members who where working that area claim to have scene photos with the bay actuator stuck in the open position and mechanically this would not be normal.

  3. FFS, they interviewed the commander in charge of the radar for a documentary. (It’s on Youtube…. somewhere) and he said they kept getting attacked by “stealth” aircraft and noticed that by increasing the wavelength they could detect the F-117As easily. Sorry, can’t be bothered to find the link but it’s out there. They hacked the radar’s alectronics for a longer wavelength and job’s a good un.

  4. Theory 1. Could be. Simple observations of a patterned behavior and exploitation of the pattern. Commonly used by all of us… like where to set a mousetrap…

    Theory 2. Nada. Theory 3. Nada. Both pre-suppose some hacking genius that we’ve not heard of since. Such a trooper would have been decorated and promoted… and we would know it.

    Theory 4. Radar stealth techniques were designed to be most effective in straight and level flight with minimal control surface deflections. Rapid turns or altitude changes expose different surfaces and the radar return becomes stronger. If the bomb or landing gear doors are open or even ajar slightly the return becomes quite large. Firing so many hostile missiles was a good tactic! Made the pilot panic, turn, climb, dive, wiggle, wet pants, use large control inputs and thus large control surface deflections increasing the radar return, turning the belly towards the radar giving a large flat plane return from the top or bottom in a hard turn, leaving still little but enough target return to lock onto. Now, had Tom Cruise been flying hot, level and straight, the plane would never have shown enough return to give the position away.

    The Commanding Officer that came up with this plan was good! Plan was only one that could give them a good shot! And it worked. Relied on inducing panic which would make the pilot forego the critical bits about radar cross-section and the specifics of same for his aircraft.

    I did ecm for a long time. .

  5. All of you are not applying the concept of KISS (Keep It Simple Stupid). Most of the time the easiest explanation is the correct one. They were able to shoot down the F-117 because it was raining that day. Water built up on the outside of the plane giving it a radar signature. The Yugoslavian Army didn’t hack or modify anything nor did they get lucky by shooting a bunch of SAM’s in the air, thats just stupid. What the U.S. Government doesn’t like to tell the world is that a lot of their military equipment is in a sense similair to a Lamborghini; it’s amazing and exotic but extremely fragile.

  6. Having worked with the U.S. equivalent to the Soviet systems likely in use at the time, most stealth aircraft get “dropped” as a bad return. Basically, the systems processing rack (a refrigerator sized computer with power comparable to a BASICStamp) says “Oops, this is too small to be a plane, and it’s a wonky, erratic return… so we don’t care about it, and we’re not going to provide SIF Paint.”.

    SIF paint is a feature of most modern RADAR systems that utilizes a combination of data available, including the IFF/SIF transponder system to label identified returns on the display. However, weather phenomena, ground clutter, and yes even stealth aircraft typically won’t be given SIF paint, as they’re not really planes to the RADARs processing system. Even still, a competent operator with a working wristwatch could’ve probably plotted a repeating pattern of erratic returns (the flight path of the F-117a squadrons) over the course of a few days or weeks.

  7. Level of stealth varies with aircraft attitude. They design for straight and level. You crank the wings over hard and your aircraft radar return goes up, stealth goes down. If a canopy, bomb door, wheel door, or anything else is ajar a large loss in stealth is realized. If you were in a hard and heavy maneuver you present a much different and stronger radar return than straight and level. Add in that the control surfaces give a large return when they are deflected, such as in hard maneuvers.

    Add simple human observation that they are following a standard path and pattern when coming over. And add the everyday observation that people make mistakes when in fear or panic.

    So.. you launch a ridiculous number of easily visible missiles to create panic, the pilot turns, pulls up, etc, and each manuever is far from straight and level such that the radar return is greatly increased making it possible track even if only from time to time, but you don’t need a lot of time cause your missiles are already all over the sky and in the vicinity. You get a paint on a target and turn torwards it…. and with that many and that much fear-of-life-panic you stand a chance of getting enough returns to score. Plus, these missiles don’t hit… they fragment when close, increasing the chances of a hit.

    I did ECM for USAF. AN-ALQ T4 V4, and ran officers through repetetive training. Did AN-ASG 21 T! and AN-ASG15 T1 as well.

    There is no hacker magik here. If there had been some hacker doing magik we would know due to promotions and medals…. and you would know their name already. This was just a really smart commander blowing away lots of munitions to create panic that could be exploited.

  8. Another fact to add, on the night in question the moon was full or near full, I remember because I was out with my telescope, over in Serbia there was patchy cloud.

    “Stealth” is a relative term, the entire airframe is designed to reflect radar signals away from the aircraft but not back to the radar station, a bit like a grazing incidence mirror.

    An F-117 pretty slow and not very manoeuvrable, even the guys that designed and built the thing called it the “hopeless diamond” because of the basic shape and has the handling of a bathtub full of bricks/wheelbarrow full of walrus’.

  9. In the book Skunk Works this incident is explained rather thoroughly. I can’t quite remember where, but regardless of that it’s a seriously good read!

  10. It could also be a result of an pilot error. It may be that the IFF-transponder was accidentally left on, and when the plane entered the enemy airspace, they could receive an responce from the IFF-transponder.

  11. If you can see the plane and have an optically guided antiaircraft missile like a Stinger, you can shoot it down.

    Or it could have been like how the Black Hawk helicopters were brought down with RPGs. Throw enough crap in the air and some of it’s bound to hit the (turbo)fan.

  12. Set up your makeshift radar systems inside of metal drums pointing at the sky in the path you know the planes will fly (they were restricted in time windows and had to fly down strict air corridors within Europe). Tune the makeshift radar to receive TV/mobile signals where there should be none. You will receive multiple triggers when the plane flies over. record your results, move the passive radar about if you need to get better trigger timing results (this was not set up in one magic day – and the entry path was exactly the same every run). Do your maths for when the triggers happen so that you know exactly where, and when, you need to launch your missiles from and how long after launch they need to explode for a good chance of downing the plane. Final run when everything is right, you still need a good bit of luck, and loads of shredding shrapnel. It is not rocket science, well actually i suppose it is :)

  13. Couldn’t the community here on hackaday create a homebrew radar system that worked on a different frequency? If I have learned anything here it’s what a few creative people can do with a few off the shelf parts.

    The radar antennas should be resonant for reception at some other frequencies that are multiple/fractions of the original frequencies even if far less efficient. Some kind of matching could be used like a coil to keep the amps from blowing due to bad SWR. A new transmitter/receiver could be easily built for the new frequencies. The end unit would be far less powerful and cover a smaller area but if they already knew where to look it might work.

    Personally I’m leaning toward human error possibly in manufacture, maintenance, or user error.

  14. When operating LO aircraft, one doesn’t always know if the RCS is as low as that which it was designed. Many actions and events in the aircraft’s life can affect is RCS, e.g., maintenance, battle damage, erosion. Scattering centers may be produced on the LO aircraft by patches of dirt, production defects, exterior damage, or incompletely closed access doors. Such conditions may go unnoticed by maintenance personnel and pilots in the field. Furthermore, repairs and production defects may leave imperfections that may not be detected by visual inspections. As a result, the aircraft may be vulnerable to radar detection. Unless the aircraft is brought to an ISAR test range, these conditions will often remain undetected.

  15. Some things already said, but some skipped:
    1) F-117 is made to be stealthy for higher-frequency radars, and Serbian (old Soviet?) radars already work in VHF-range. You cannot (yet) make something to be invisible in full-spectrum of EM radiation, and people who made F-117 made choice to cover it from newer Russian radars. No hacks needed, only skilled operator and working radar.
    2) Standard procedure in AA combat using S-125 (called Neva in east) is to fire two rockets (out of four present on launch pad) at one target. No “salvos” nor “barrages” can be fired with that system. Rockets are guided by following radar beam from ground-based radar.
    3) Dani Zoltan is excellent troll. He was not at the “cabin” at the time of shooting-down, it was not his shift, no “additional homemade hackerish devices” were used…
    4) If airplane is already stealthy, and looks like a bird on radar screen, how can it reflect enough of radio, tv and cellular radiation to be spotted? And how can radar recieve all those signals that are out of its frequency range?
    5) Serbian forces did not have (and still do not have most of following) laser guided AA missiles, IR target finders, Tamaras, Veras, AWACS, flying saucers, alien alies, nor wizards.

    Care to do some investigation? Find out what fell in Spačvanske šume region in Croatia? What happened afterwards with location? How many B-2’s are still functional?

  16. Throw a large number of bananas into the air and follow the delicious scent of baked banana goodness coming out of the engine of the aircraft. It help if you also have a team of hungry spotter monkeys arranged in a grid covering the territory your are trying to protect.

  17. I’m from Serbia and my family fled from the country as the bombings became more and more aggressive. I still remember they shot down the plane, as it was on every local TV channel. One of them had interviewed the responsible soldiers. They explained the bomber was visible to them while the bomb bay was opened. Although I can’t remember he mentioned they modified the radar, he mentioned it was an old russian type they used. So I would go with theory 2.
    Why exaclty is such a modification necessary for the theory?

  18. There was an article in greek magazine ptisi saying that they were homing on the aircraft Radio-Altimeter back then -USAF- use Radio-Altimeter to flight nap of the terrain using spy satellite radar maps so yes limited if not the same route over again plus a small beacon “planted” in the aircraft that did the job.

  19. I am from Serbia, and I was bombarded among other people here then.. And I remember when they shoot it down..
    Here I heard that stealth plane were accompanied with several other planes and they were flying in formation (stupid). So radar guys seen planes and seen that there is no “head” of formation and just shoot there where should be plane in formation.. :)

    So, that is theory no. 4…

    Fanny thing was, after plane crashed, army was there, probably collect some of things and left other stuff there. Some gypsies came and collected it like it is worthless crap.. :)
    And small kids used to have joke: “Look I have part of that plane” showing empty hand opened. And if you ask where is it, they would laugh “here on my hand, it is invisible.. ” LOL…

  20. I worked for the first 3 years out of school in the low observables field. According to the “in the know” folks, the plane was detected via an array of nodes consisting of people watching multiple TVs set to different erroneous TV channel frequencies in the VHF band. When the aircraft was bombarded with a presumed A-band radar the redirected wave energy (what faceted stealth aircraft tries to do, besides absorb)would cause a visible & audible change in the TV’s within a relatively small distance to the aircraft (Theory 3 in the VHF band). I can’t remember their explanation of actually getting the missile to intercept.

  21. I think I know the answer! and it’s hacking the radar.
    In the prime of Iran’s revolution, the Iranian revolutionary guard installed some anti aircrafts around Jamaran, where the leader lived. It was because they feared being attacked by the US, in order to bring the Shah back. My father was an army general and he told me many times during the night these anti aircrafts shoot and it was because they made it so sensitive, they even detect a bird and shoot it down! So, it’s possible to hack a radar to lock the anti aircraft to even a bird and shoot. And the strealth aircrafts are like large birds in the eye of a radar. We don’t know how many S125s were fired that night to one hit an aircraft and the others hit regular innocent birds!

  22. Oppps! HAD started using a 2nd page if there are large numbers of posts. Didn’t know that. Pls excuse my dupe posting.

  23. The F117 stealth aircaft (and an B2 bomber too!) was shot down by an “Yugoslav” colonel (who has Hungarian ancestors, and derived from Transylvania ;) ) Zoltán Dani and his team. They used Sz-125M Nyeva anti-aircraft missile system and a modified P-18 radar.

    So the second theory is right

  24. Actually…prior to 2011 (on this particular “b” model), heat signature combined with certain weather conditions, would allow the very basic radar to find the 117. We have now, somewhat, cleaned that up.

  25. Сами виноваты! Надо было предупреждать, что этот самолёт — невидимка. Мы бы тогда сбивать не стали.

  26. I didn’t read every reply :( sorry – but my own take is Doppler effect. I believe a lot of what’s been said before could be possible too as the plane just wasn’t that great as we’d like to imagine. At said time that is however, previously it was great – just once identified to “public” a weakness would be found, and it was. However, one that did require some luck.

  27. Nicola Tesla before he died , he gives to his countryman special blueprint for all seeing radar.I am from Macedonia ( former republic of Yugoslavia) and i know form a friend who works in the army, and he speculated that we have some other crazy stuff hidden.

  28. It was not luck at all. First a little remainder – old Yugoslavia (SFRJ) was one of the biggest arm manufacturers in the world, and had one of the most powerfull armies. After decomposition of old country advanced knowledge about modern weapons remained and is being improved on.
    So both NEVA rockets and P18 radar were heavilly modified (some companies are offering this service commercially). Weather was not good, and airplane is shot over the flat land.
    A lot of antiradar missiles were deployed by US so Serbian radars were operating in specific mode – 30 seconds of operations, then relocate to another position and repeat. It was possible to sense F117 multiple times, obtaining possible trajectory, which enabled that next position is choosen in such manner to enable locking and firing the missiles. For this round, radar was left on 45 seconds to obtain lock and 2 missiles were launched before relocating, one of them hitting the target.
    Btw, it was not just one F117 that was hit by Serbian forces, one fallen on the Serbian ground so it was not possible to hide it. At least 2 more were taken down, one felt into the Bosnia on teritory controlled by muslims and UNPROFOR succesfully isolated site before anybody could gain proofs, other felt in Romania, again under NATO jurisdiction.

  29. Definitely hack, there is quite few videos in Serbian floating internet with Dani giving general explanation how they did it. Dani refused more than three multi milion offers by foreign armies to sell his knowledge and radar improvements. They made documentary movie about Dani and Zelko meeting after the war https://www.youtube.com/watch?v=bVQLiijbqRw
    This movie really restored my faith in humanity

  30. Stealth aircraft are only stealthy from some angles, as they rely on a mixture of absorbtion and reflection in a different direction from the transmitter.

    This makes the assumption that the transmitter and reciever are coproximate. If you separate them, ideally such that the line between them is parallel to the direction of the target aircraft’s path – easier than you might think by careful siting of AA and similar – and you get a strong “return” signal, making detection straightforward.

    Consider trying to illuminate a flying flat surface at an oblique angle with a torch. The reflected light from the torch is bouinced away from you, making it hard to see. If you get someone to shine the torch from the opposite side of the surface from you, then you can see it very easily, along with any other surfaces flying towards you.

    Radio transmitter/reciever pairs are only located close to each other for reasons of practicality. It wasn’t always so, and they don’t need to be. If you can also use a frequency different from that which the metallic spherules embedded in the aircraft’s paint are the optimal size to scatter, then it makes it even more certain that the pilot is going to have a long walk home.

    Has the F117 flown any combat sorties at all since then?

  31. Maybe it was already said here, I didn’t read every post…. “Stealth” means “Low observable” NOT “Invisible”…. If a bird gets close enough and it has an IR seeker, it is probably going to be able to engage…. the same holds true for seeker head radar proximity fusing… and it is possible that plain blind luck resulted in warhead “salvage fusing” that tells the bird to blow if there is a “signal anolomy” (i.e. a track is suddenly lost)

  32. The sky is big…
    To make this happen, the soviets would have to determine the appropriate Timing, angle, range… etc… to an unreasonably high precision.

    Therefore,
    either they were able to detect it, or they were able to narrow down the angle, timing, range etc… by interpolating patterns.

    Assuming the soviets knew exactly when, I would think that the “where” could easily differ by several hundred meters. It’s unreasonable to assume that the pilot could fly through his target zone precisely enough to allow for a lucky hit.
    Not to mention that the aircraft itself is supposed to be very difficult for guided missiles to track.

    However, If the soviets HAD detected a pattern they would have learned what general part of the sky to watch. Fill that region of the sky with some variety of energy (RF, Lasers, anything that would react to a big metal something flying through it…) and when you see something weird, Fill that space with angry things.

    So, probably some luck, but almost definitely some strategies to minimize the amount of luck required. After all, I don’t think they would tip their hand unless they had a reasonable certainty of success.

  33. I read an article about the stealth technology in F-117. I believe it was in an EAA mag, but I can’t be remember. The gist of it was that a lot of the stealth came from the special coating on the plane. When the planes had to be serviced, the thick coating had to be removed to uncover the access panel. The paint was very expensive and in short supply. It also required a specific procedure to re-apply it to the affected area to maintain the stealth profile.The USAF ground crews did not like dealing with it and often did a poor job replicating the original coating (sometimes despite their best efforts).

    I’m not saying this applied to the specific case in question, but it could easily explain a loss of stealth characteristics.

  34. As people have pointed out, the plane was not invisible. This has been somewhat common knowledge even before the airplane was hit. The French broke the news that it was not very hard to detect the plane.
    On top of that, how many non-stealth airplanes has been shot down, I know it happens occasional but compared with number of flights being made, the answer is close to none.
    The explanation that this plane was downed has mostly to do with that the US was foolish and started to believe it was invisible and that it was impossible to hit.
    What’s even more interesting is why this site did go down the drain.

    1. Also worth noting is that the Serbs were no hillbilies when it came to AA fire. The Russian school wasn’t that bad at all…

      1. I think you misunderstood something there, the Serbs where obviously cave men throwing rocks at this invisible aircraft. That they could down the plane is at the same level as if Jesus would shot down Santa with the avada kedavra curse. We need a conspiration and possibly a religion or two to explain this.

  35. The point everyone here is missing is:
    1. It didn’t matter if Humans could see the plane.

    The ability to hit the planes lies in the targeting systems in the missiles. According to the Wiki link from hackaday, if I am reading right, is guided by an accompanying radar based targeting “pod”. The amazing bit is that radar on this pod had to pickup, track, and constantly update the info to multiple missiles at once. All on basically Vietnam era technology. The fact that this feat was possible boggles the mind. But then I remembered that at least through the late ’90s, the Space Shuttle for NASA, only had 8Mb of RAM for all on-board systems!!! 0_o

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