Pilot friend of mine says they do occasionally get alerts from ATC for unidentified primary radar targets near their aircraft while in flight. Usually this turns out to be a flock of birds, bunch of Mylar party baloons and such but in light of all these reports “We’ll be looking a bit more closely for flying tic-tacs now!” ;-)
If anyone saw an airliner on their radar, they probably wouldn't even try to confirm what it was. If they saw an unidentified object, then they'd call someone.
ATC radar regularly loses small planes on 'primary' radar (primary radar being pure radar), and has to rely on the transponder. There are many areas where you simply don't have primary coverage, especially close to the ground. I've flown through military controlled airspace where they lose radar contact with me in a Cessna less than 10 miles from the base.
The primary surveillance radars at airports are unlikely to detect an object as small as these, they just don't reflect enough and I suspect even if observed they would be ignored by software because of their small size and low speeds (basically, they do not look or act like airplanes).
The secondary surveillance radar, which is now the main system used by ATC, would be completely blind to them, as it relies on active equipment being installed in the aircraft. Requiring the installation of transponders in drones might be tempting, but they are large and expensive compared to a quadcopter, so it's impractical.
Any large set of hovering things grouped tightly enough to ensure damage to a passing F-22 would definitely show up on radar. Flocks of birds show up; a flock of drones would too.
Non-tactical aircraft don't really have radars like this to spot other planes.
TCAS exists and can provide collision warnings and some degree of information on where other aircraft are using secondary radar data, but it's very much a last line of defense.
Both planes are expected to see each other, and they're also expected to hear each other on the radio.
Cute, though I suspect the FBI have known the public knew about this, and alter their patterns for the most sensitive investigations. The real deal would be detecting when aircraft are in any cycle, regular or irregular, with similar visibility of a set of likely “targets”.
Primary radar is good enough to pickup a 2500# single engine airplane from 50+ miles away.
I flew from Detroit to Boston a few years back in a 4-seat, single engine airplane after an electrical failure. On a hand-held radio and with no electrics, ATC had a good primary target on me the entire way (at 5-9K feet). On controller handoffs, I would have to turn north for 1 mile for them to confirm the primary target they were looking at was me.
Up and down the Eastern seaboard, I pretty regularly get traffic called out as "primary target only" which also means ATC has no idea of the altitude. Those tend to be low, slow moving aircraft (often without electrical systems).
Another interesting aspect is the Lock-On detection of the enemy aircraft. Aircraft are able to identify when they're being tracked by other aircraft or homing missles. [1]
Regarding posts about spoofing and maintaining radar, it was my understanding that the radar sets that most ATCs used was not actually powerful enough to get direct returns from commercial aircraft, and relied on amplifying transponders to be able to see them. Supposedly only militaries operate radars powerful enough to see aircraft directly. Can anyone who knows more confirm or deny? If that's true, I guess we're already in a world were ATC info could be spoofed.
> It's secondary radar so it only sees planes with a transponder, but that's usually all of them.
In particular we're talking here about aeroplanes on an approach to a major airport (if they aren't on approach then by definition they aren't choosing between ILS and a visual clearance, and if it isn't a major airport why are we trying to bunch them up more?).
All US major airports have a "Mode C veil" which means there's a regulation requiring aircraft near those airports to have transponders ("Mode C" is a transponder mode in which the aircraft reports its own assessment of its altitude based on air pressure as well as a four octal identifier).
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