O.K., maybe I’m an idiot, but the news this morning indicated that outside of Boston, a United 757 had a near-miss collision with an F-117A Stealth Fighter on a training mission.
The idiot part of my question is, how the hell did the airliner ever know? They say the collision warning system on the airliner indicated they were close to hitting another plane. Ummm…last time I checked isn’t the ‘stealth’ part of a stealth fighter supposed to indicate that it is INVISIBLE to radar? Is the stealth feature something they can turn on and off on the F-117A. I thought the general shape of it made it look like a bird or other non-threating object on radar.
Whoops, that should read ‘near miss’ OR ‘near collision’. They didn’t ACTUALLY hit each other. The Air Force has now said they weren’t actually that close together now. The CNN story is at:
I don’t think the collision warning system aboard commercial airlines depends solely (if at all) upon radar. I seem to recall pilots saying that they use a type of transponder? to detect other aircraft. However, I don’t think all planes have these and I would really be surprised if stealth aircraft did.
Stealth aircraft are equipped with stuff to make them “visible” to radar when they are not in attack mode. I would think that a training mission over New England would require that the identifiaction equipment be turned on (as opposed to a training mission over Nevada where they would leave it off and stay out of the standard flightways).
Another thing to consider is that the F-117 is not absorptive of radar like the B-2. The F-117 achieves its stealthiness by using flat surfaces, which will reflect a radar signal very well in one direction each. So a radar far away on the ground would be unlikely to have any return signal, except those very few and very brief occasions where one of the flat surfaces was pointed right back at the radar. Those few times, the operator will think that it’s some kind of bogus noise.
But closer up, like right below another plane, it could be reflecting a large amount of that plane’s radar. At least this is the explanation I came up with when I read the story.
I remember hearing that the surface of the F-117A is carcinogenic. How so? What would you have to do to get cancer from it? Touch it? Lick it? Do that for like a year, 20 hours a day?
The F-117 is equipped with a removable radar reflector just so it CAN be seen when it needs to be. Maybe this one didn’t have it on?
Newer commercial airliners do indeed have the TCAS transponder system so they can detect each other and take evasive maneuvers if need be. The TCAS systems “talk” to each other and play an audio instruction in the cockpits (i.e. “Whoop! Whoop! Pull up! Pull up!”). They are not used on military aircraft (yet), nor on older airliners either.
I could be wrong on this, but I though that ALL civilian aircraft, even down to Piper Cherokees, are required to have an identification transponder “squawking” while in flight. My further understanding is that this transponder signal is generally what the ATC radars, collision-avoidance radars, and such are detecting. That’s a bit different from the radar blasting out a signal and listening for the return “ping” - I’ve heard warnings that planes with nonfunctioning transponders are invisible to most control tower radars. Can somebody confirm or correct this?
Military aircraft also have such transponders, and I’m sure that they’re required to have them on when operating in airspace that’s not off-limits to civilian aircraft. To do otherwise seems homicidally stupid. Obviously, when you’re trying to hide it’s another matter…
Is it just me, or is that “757” in the photograph at the top of the article not clearly a 747? :eek: 757’s don’t have a large hump containing a 2nd deck. At least they got the manufacturer right…
Not all civilian aircraft are required to be equipped with transponders. Class B airspace (your typical large airport – LAX or SEA, for example) has a “30nm Mode C Veil”. Mode C means that you are equipped with and are using a transponder that transmits altitude information. Mode C must be used whenever you are flying within 30nm of a Class B airport. As long as you’re flying in an area that doesn’t require a transponder (I’d have to pull out my FARs and AIM to get the specifics – I’ve never flown without a transponder), you don’t need one. Even if you’re flying an airplane that doesn’t have an electrical system, you can fly in areas that would normally require a transponder, radio, etc. as long as you make prior arrangements with the controlling agencies.
What a transponder does is send out a signal that says, “Here I am!” It is “interrogated” by ATC’s radar, and “replies” with a coded signal. You may be told to “squawk 1204”. In that case you’d tune the transponder to 1204 and that’s how you’d be identified on ATC’s screen. You can squawk 1200, which is the “general” code. If you haven’t been assigned a code, that’s the one to use (usually).
I was flying a Cessna 172 in the L.A. area, and the transponder was not working. We “squawked and ident-ed”, but ATC was not receiving our transmission. They were able to get a “skin paint”, though. That is, the radar signal bounced off of us and back at them.
Military aircraft have IFF – “Identification, Friend or Foe”. I’m pretty sure this is their version of a transponder. The IFF is interrogated and returns a friendly signal. No signal means the target needs to be investigated.
>> No signal means the target needs to be investigated
I guess that’s military speak for shoot first, ask questions later.
>> Another thing to consider is that the F-117 is not absorptive of radar like the B-2. The F-117 achieves its stealthiness by using flat surfaces, which will reflect a radar signal very well in one direction each.
This is so easy to visualize. Sit in a room with a lightbulb just behind and above you and he someone hold a polished, rounded metal object in front of you at a certain distance. No matter the angle you get a reflection because at some point of the object the angle is right.
Now have that person hod a mirror. Unless the mirror is in the exact requiered angle you will see no reflection.
Slight nitpick - it is not INVISIBLE to radar, of course, just harder to see. I would guess that even in stealth mode, if an F117 was this close to a radar, it would be visible.
IIRC, the F117 has roughly the same radar cross-section as a large bird. Sadly, most radars are smart enough to realize birds don’t travel at several hundred miles per hour…
Smeghead,
There are lots of birds that fly at hundreds of miles an hour! They are the ones splattered on the fronts of all the various jets we are talking about!
Regarding this friend-or-foe transponder thing, again, forgive my naivety on this having never flown a plane…Don’t the enemy planes have a system to figure out the correct message to send back that makes them ‘look friendly’? I can’t believe with all the advances we have had over the years that something like mimicing a ‘friendly’ message can’t be done.
Then again, I am assuming this is a fairly simple thing. In reality, I’m sure it changes for every mission and every squadron, etc. Still, I would think there would be a way to capture the signal from another ‘friendly’ and use it yourself to raise havoc if you were the enemy.
I believe the radar cross-section of an F-117 is more like a marble than a large bird. One of the problems when building it was that they had to figure out how to make a cockpit so that the pilot could see out without radar seeing in. The pilot’s helmet would appear far larger on radar than the plane otherwise.
Also, the F-117 is coated so as to absorb radar. The reason it has flat panels and the B-2 doesn’t is that when the F-117 was built, it was too difficult to perform the necessary calculations to determine how the radar would reflect for curved surfaces. By the time the B-2 was designed, they had computers capable of that sort of thing.
>> …Don’t the enemy planes have a system to figure out the correct message to send back that makes them ‘look friendly’?
Yarster, I know nothing about this but I figure it is quite easy to exchange encrypted information.
Suppose I am the AWAC coordinating the whole thing and I send a message out: “The question is 155, what is the answer?” the friendly plane says “I am your friend Black Cat, your question is 155 and this message is digitally signed with my signature”
Since the question is changing continously and the response is too, how can the enemy mimic it? The only way is to decrypt the key to the signature
Those cheeky b***ards! They done changed the picture since earlier today. The one up there now does, indeed, have a 757. Earlier, there was a photograph of a United 747 parked at a gate, right above a caption identifying it as a 757.
One more point - the closer you are with a radar, the easier it is to get a return signal. The return signal is inversely proportional to the distance raised to the fourth (!) power.
Mode 4 of the IFF transopnder system is made up of an encyrption system plus a key that is changed daily worldwide. The key is programmed into the transopnder with a mechanical device on the ground so that the key itself is never transmitted. Capturing a box that has been keyed does little good as the key is erased when the box loses power or the cover is opened to program the key. I’d describe the key guns used for the APX-72/76 and the UHF radio encryption but then I’d have hunt you down like a dog and…I’ve said too much, time for the amnesia ray.
