TCAS/UFO

[commercialdriver]

While on the bridge departure from JFK, my TCAS showed a target converging and we had to take an evasive action. The radar controller was asked about this airmis. He simply said that it was a UFO and his radar didn't show anything. How did it get on my TCAS? if there was no XPDR on board the UFO?

[10W]

Were you given evasive action by the TCAS (i.e. climb/descend) ? If not, what evasive action did you take and why ??



------------------
10 West
UK ATC'er
[email protected]

[FurryDice]

I have seen quite a false few contacts on TCAS 'dance' around the aircraft before now, causing a 'TRAFIC' alert but as yet never had an RA. Last one I saw (last week) started from behind the aircraft accelerated rapidly past the left wing and disapeared. Nothing seen. Seems to be a TCAS thing....

[Three-Twenty]

cd - as 10W asks, how did you take evasive action? Based on the lateral display alone?

I would be extremly reluctant to manoeuvre based on lateral info from the TCAS, having seen (VMC) the frequent difference between where the aeroplane IS and where the TCAS says it is...

Have to agree with Fuzzydice - TCAS seems quite funny sometimes

PS I hope you don't mean that a 'UFO' is extra-terrestrial...if it was, how did he get a slot? :)

[RATBOY]

Radar feed for New York TRACON is a wierd and wonderous thing... 6 different primary radars and at least as many secondary (beacon) all mixed carefully (not shaken) and filtered to construct the display the controller has.

Be tempted to say it is a "TCAS thing" and there really wasn't anything there.

[Capt Pit Bull]

Try a search on TCAS.

There have been several threads about TCAS, and one in particular about target peculiarities.

I'm too dumb to figure out how to post a link, however if you also search on my user name you should find it.

Another possibility is that the traffic in question was being filtered by the radar.

E.G. Controllers may filter out certain sqawks, e.g. 7000, to declutter their display and make it manageable. However, if someone with a filtered sqawk gets lost and goes somewhere they shouldn't....

CPB

[This message has been edited by Capt Pit Bull (edited 15 October 2000).]

[Galla]

Flying overhead Southend target 800' below and climbing rapidly. We got a TCAS warning:
"CLIMB,CLIMB NOW"
Radar couldn't detect anything. It scares the hell out of you.
Apparently it is a TCAS fault.

[Midnight Blue]

Recently we saw a 737 shaped UFO with the letters "AIR BERLIN" on it, overtaking us about 1000ft higher. There was nothing to see on TCAS display. Other targets were shown properly. I wonder, if we got the Walmart-Version of TCAS or if the 737 collegues broke their transponder?

[Dan Dare]

I've had a number of aircraft reporting TCAS traffic at about 4 mile final where there is blatantly nothing on the radar in controlled airspace where I do not believe there was any traffic. One reported traffic in a position which was below gound level!

Is it possible for an interrogative squitter to trigger a reply from a ground reflection?

I sometimes lose some SSR replies due to the angle of climb/shielding of aerials for a number of sweeps. I expect this would also explain the Air Berlin.

I still want to know what stops ground TCAS trials from triggering TA/RAs when they are pumped up to altitiudes above surface.

[Midnight Blue]

Might be the connection to weight-on-wheel-switch?

[Lucifer]

Slightly off track, but I have heard of some radar systems not picking up light aircraft, as they have been filtered to only pick up things at speeds greater than 110-120kts. Sounds silly, but it is true: ie. you might pick them up, but not ground based radar.

[RATBOY]

The ATC primary radar uses a number of electronic tricks to avoid useless targets. One of the tricks is a moving target detector (MTD) that filters out any target moving slower than some certain speed. There are also filters to dump out "targets" that appear on one sweep of the antenna but don't appear on subsequent ones. With modern software controlled primary radars you can specify an azimuth/range/altitude to ignore the target return from because you know there is a building/billboard/whatever there but not an aircraft.

Secondary (beacon) radars rely on the transponder response with codes, altitudes and such and sometimes the beacon doesn't respond for a time around or two or the interrogation pulse isn't received. For this reason ideally the targets on the ATCO's tube is made up of an integration of primary and secondary returns on the theory that if one doesn't work well the other will and the targets provided on the display will all be valid and all have a pretty little data block attached.

TCAS uses the transponders of equiped aircraft and will either interogate itself or use the transponder replies to ATC interrogations depending on the flavor of TCAS you have. The raw responses are processed and displayed and in the ultimate version of TCAS resolution advisories provided based on the logic embedded in the TCAS firmware.