ATC primary radar is pretty weak. Not showing up (particularly after changing flight direction) doesn't mean much. It's very odd (and illegal) for something to be up in flight levels without a transponder though.
Yeah I've heard stories of some people doing crazy, dangerous, illegal things in small planes and just turning their transponders off.
I was a passenger in a C182 once where the transponder antenna fell off midflight. It was very educational how much trouble ATC had seeing us. Even after telling them exactly where we were, flying the heading they gave us to present the broadside of the a/c to the radar antenna, they basically said "there's something that might be you there, but I can't really tell."
A big jet at FL370 should show up on primary, but I can see it depending on a bunch of factors.
I can’t read the article (paywalled), but I would expect primary radar isn’t going anywhere around airports.
We still have it, and our commercial planes have been required to have ADS-B transponders here for more than a decade. This is just for en-route tracking.
Yes. I am astonished that you do not already know that.
On 9-11, the combined maximal efforts of civilian and military aviation were unable to locate four airliners because their transponders were turned off. This occurred near the New York and DC metropolitan areas, some of the most carefully controlled air space in the world.
Without a transponder, an aircraft is just a raw radar return among, potentially, hundreds or thousands of other returns from civilian and military aircraft, weather, birds, balloons etc. Add to that glitches, ghosts and anomalies in busy air space and it is not surprising that a large aircraft without a transponder can hide in plain sight.
Have they said whether the transponder was active on the jet? They usually have the ADSB beacon live when flying near airports, but if it was turned off it would be a bit trickier to find. Also, if the retroreflector wasn't extended it might be hard for active radar to track it as well. Worst case scenario would be if it was in "full stealth" mode -- that would be the situation where we discover that NORAD air defense systems can't detect our own jets!
Secondary radar is very much alive in the US. Forget to turn on your transponder (whether or not you are ADS-B out equipped) and how long until ATC notices? For me, it's usually been before I'm through 400' AGL. Or, as tjohns mentions, just look at how often your reply light flashes.
From the FAA itself:
"The Mode S SLEP Phase 2 program will implement modifications to the Mode S system to sustain secondary surveillance service through 2028."
It’s not just about seeing you, it’s about seeing everyone around you too. ATC’s job is to separate aircraft and they can’t do that if they can’t see non-ADS-B aircraft. In fact just today I overheard an approach controller vector an American Airlines jet around VFR traffic at 1700’. That VFR traffic was in “non-rule” airspace, where ADS-B isn’t required. (I saw the jet and the VFR traffic from my cockpit.) They won’t be able to do that without radar.
That isn't really how it works. Low observable aircraft flying in friendly civilian airspace generally have radar transponders turned on specifically to make themselves visible to air traffic control and prevent collisions. Those transponders are turned off for combat missions. And ATC mostly doesn't use primary radar any more so they don't even get skin paints on regular aircraft.
No commercial aviation radar system even tries to output non-transponder altitude infomation. Many are secondary only and don't even pick up targets without transponders.
Military primary radar, like the one that picked up MH370, obviously can.
But I don't think any of those are designed for really accurate altitude measurements. That job is usually done with targeting radar which (at the expense of not being able to see multiple targets) can lock a single target and get it's exact position.
that you can turn on if you are flying into controlled airspace.
What I think they should have is a new system that pings the location and other data to satellites that can't be turned off and will work anywhere unlike radar transponders.
You only need a transponder when flying an aircraft in controlled airspaces (Class A, B, C). You can fly without a transponder in a lot of places as long as you are in VFR conditions and not within 30 miles of most airports. It's just not a good idea. This is why gliders and paramotors can fly without a transponder in VFR conditions.
This is just basic safety for vehicles that can't see each other traveling at 100-1000 miles per hour in conflicting space.
Although it's a little concerning that ADS-B makes it so much easier to identify WHO is flying the planes.
>Why hasn't it been made mandatory that all aircrafts should have a standardized transponder ?
In some parts of the world, it may be. For example, I don't know if Europe allows for aircraft without transponders. Even in the U.S. you must have a transponder to enter certain types of airspace (e.g. the airspace around major airports). As far as I know, no matter where you are in the world, you must have a transponder to fly IFR.
Installing a transponder is a non-trivial expense, especially in older aircraft (which are the aircraft most likely to not have transponders). For a lot of small aircraft in the U.S. this would represent an unnecessary burden on the owners. For example, crop dusters: they typically fly around low and slow in areas with very little traffic, under day VFR conditions, so they have no need to interact with ATC and therefore no real use for a transponder.
>It scares me a bit that, at the end of the day, we rely on pilots avoiding collisions by sight.
We don't rely solely on this: we have transponders (with TCAS in some cases), ATC radar, and (in some cases) airborne radar. All of these tools help us to avoid collisions. Unfortunately, none of them are 100% effective, and in most of the situations where they all fail, the good old Mark I Eyeball usually saves the day. See-and-avoid isn't perfect, either (if it was, we'd never have midairs), but it is still the most effective tool available for avoiding an impending collision.
Civilian air traffic control relies mainly on secondary surveillance radar including aircraft transponders, plus ADS-B. Primary radar coverage is limited to larger airports plus a few border and military areas. An aircraft can hide pretty effectively in most US airspace by just flying low with transponders switched off.
According to Flightradar24, https://twitter.com/flightradar24/status/1742136715253313938, the Japanese coast guard aircraft was not equipped with a ADS-B transponder. Probably because it's not a requirement for military aircraft. That can explain why the ATC and/or JAL was not aware of the exact location of the plane.
Inside the continental US, if you fly a small not-turbine-engine-powered airplane yourself and only go to rural airports with no tower, it is actually legal to have no transponder (see below, 91.215(b), 91.225(b)).
But, if the transponder is installed, you are legally required to turn it on at all times no matter where you are (see 91.215(b)(3), "all controlled airspace" means everything above 700-1200ft AGL (depending on exactly where)).
So for this to be legal, you can't just turn if off: you have to actually remove it from the airplane. Whether that is legal additionally depends on the airplane.
I gather that the point was they didn't require someone with radar to see them, they turned on ADS-B so it would show up on all the usual flight tracker sites.
reply