Ships Appear on TCAS

[Charles the Equestrian]

Out of curiosity, is there a reason certain ships (perhaps, military or Coast Guard) appear on a TCAS as a primary target? Recently, a ship has moored itself near the approach I frequent and it's a bit disconcerting to have to fly past that thing in IMC. We have verified this target as a ship, and we're not low either, probably 4000 ft when we first pick it up. Any knowledge or reasoning for this?

Thanks!


Charlie Ho!

[AuxBatOn]

Well, TCAS works on transponder return. Therefore, I think it's fair to assume that the ships has a transponder.

[Lurch]

It has a transponder?

I have picked up semi's on the highway before, another reason not to fly low.

Lurch

[taylor498]

If it's a primary target, wouldn't it's physical presence be enough to see it?

Correct me if I'm wrong but primary radar has nothing to do with a transponder return, just the signal bouncing off something. Doesn't TCAS work off xponder (secondary) returns only?

[GoinNowhereFast]

I know larger trucks are required to have things called transponders for the 407 ETR to collect the toll, but I doubt they'd work on the same frequencies as aircraft transponders.

As for ships, I know they have RADAR, harbor controllers and the such. Transponders in ships would only make sense. I would have thought they'd use a different frequency though.

[AuxBatOn]

You could see a ship with primary radar, sure. You can see birds, cars on the highway, everything that is big enough. I'm not sure if there is a velocity gate on the primary radars, but that would limit what you see.

TCAS works on transponder returns. Period. Unless your aircraft has a radar that can detect other airplanes (which I doubt you have), your TCAS returns will be based on transponder.

[Lurch]

Unless your aircraft has a radar that can detect other airplanes (which I doubt you have), your TCAS returns will be based on transponder.

How else would you expect my missles to lock onto those trucks going down the highway. It's really hard hitting those darn things with dumb bombs.

Lurch

[C-FABH]

The issue is that ship transponders do not transmit altitude data. Therefore the TCAS shows it as a ship 'in the sky'.

[AuxBatOn]

The issue is that ship transponders do not transmit altitude data. Therefore the TCAS shows it as a ship 'in the sky'.

Just like any mode A return, it will show a return. Period. It doesn't know if it's in the air or on the ground. It knows it's there. If someone with a mode A leaved his transponder on while taxiing, you'll see the same thing.

[Tim]

is it possible that its a helicopter onboard a military ship?

[bater]

Strange, they seem to operate on very different frequencies.

Ships AIS system(Transponder) Default frequencies:
AIS1 161.975 MHZ
AIS2 162.025 MHZ
AIS/DSC Transmitter:
Power output: 12.5 W or 2.0 W
Frequency range: 156.025 - 162.025 MHz


Aviation Transponders:
"All Aviation Transponders work on 1030 and 1090mhz. (which does fall in the L Band range)"

[AuxBatOn]

What would be relevant is what frequency does the TCAS receives. While it could be the obvious (aviation transponder range), maybe they can receive different frequencies.

The helo on a boat (hmmm ship) theory may be plausible. Did this happen close to Esquimault/Shearwater?

[iflyforpie]

For you to get a TCAS return, it not only has to be on the proper frequency, but it also has to respond to the unique interrogation from the TCAS unit. For this to be random would be quite unlikely.

[Spokes]

Military ships do indeed carry transponders. these work on the same 1030/1090 MHz (1030 for interrogation and 1090 for reply) system as aircraft transponders do. The also use the same octal coding system as aviation units do. These have nothing to do with the AIS system. That is something completely seperate.

As an aside, warships are also able to interrogate transponders, so they can see your transponder, as can radar operators on Aurora aircraft.

BTW transponder returns are 'secondary' returns, radar echo's are 'primary returns.

[Intentional Left Bank]

Unless your aircraft has a radar that can detect other airplanes (which I doubt you have)...

Not relevant to this discussion, but for interest sake, the 737NG has a weather radar that can accurately and consistently paint other aircraft out to twenty miles.

[Invertago]

I heard ATC giving a traffic advisory for either a slow aircraft or ship near YYJ once. They were not sure what they where picking up.

[Donald]

Military ships do indeed carry transponders. these work on the same 1030/1090 MHz (1030 for interrogation and 1090 for reply) system as aircraft transponders do.

However they don't always differentiate between friend and foe...

US shoots down civilian airliner
In the course of these escorts by the U.S. Navy, the cruiser USS Vincennes shot down Iran Air Flight 655 with the loss of all 290 passengers and crew on 3 July 1988. The American government claimed that the airliner had been mistaken for an Iranian F-14 Tomcat, and that the Vincennes was operating in international waters at the time and feared that it was under attack, which later appeared to be untrue.[46][48] The Iranians, however, maintain that the Vincennes was in fact in Iranian territorial waters, and that the Iranian passenger jet was turning away and increasing altitude after take-off. U.S. Admiral William J. Crowe also admitted on Nightline that the Vincennes was inside Iranian territorial waters when it launched the missiles. At the time, the captain of the Vincennes claimed that the Iranian plane did not identify itself and sent no response to warning signals from the Vincennes. Apart from Iran, other independent sources, for example the airport of Dubai, have confirmed that the plane did indeed identify itself to the American naval ship and also confirmed that "the civilian aircraft was ascending and therefore could not have posed a threat," agreeing with Iranian officials.[17]

According to an investigation conducted by ABC News' Nightline, decoys were set during the war by the US Navy inside the Persian Gulf to lure out the Iranian gunboats and destroy them, and at the time USS Vincennes shot down the Iranian airliner, it was performing such an operation.

In 1996 the U.S. expressed regret only for the loss of innocent life, and did not make a specific apology to the Iranian government.[46][49]

The shooting down of a civilian Iranian passenger plane Iran Air Flight 655 by the American cruiser USS Vincennes, was cited by an Iranian scholar[who?] as apparently giving Ruhollah Khomeini reason to withdraw from the conflict:[50]

An Iranian scholar present at the conference said a turning point in Iran's thinking came with the shooting down of an Iranian passenger plane in July 1988 by the American cruiser USS Vincennes. That incident apparently led Ayatollah Khomeini to conclude that Iran could not risk the possibility of U.S. open combat operations against Iran and he decided it was time to end the conflict.

[Spokes]

Ah yes, I remeber when this happened. There are several different 'modes' of transponder signals. To military radar operators, mode 3 is the label given to standard civilian transponders. 3/A for position info, 3/C for altitude. There are also 3 other 'modes' of transponder- 1, 2 and 4. The signal is basically diferentiated by the spaceing of a pair of framing pulse doublets around the octal code pulses. Modes 1 and 2 are set similar to how you would set your civilian transponder. Mode 4 is set with a crypto-coding device.

On most military aircraft of that day, the standard transponder used by military aircraft was the AN/APX-76. It was a single transponder unit, that function in modes 1, 2, 3, and when the proper crypto device was available, mode 4. Civilian transponders of course do not have all these modes available.

The Iranians unfortunatly did alot of mixing and matching of equipment. The air defence operators that day saw an aircraft that responded to one or more of the 'miltary' modes when interrogated. Because of this, they assumed they were tracking a military aircraft, likely one of the tomcats Iran had. I believe that in the aftermath, it was assumed that a working transponder was taken out of a derelict tomcat and swapped into a civilian airliner- or at least that was the theory I heard at the time. The overall circumstances were more complicated than what I have outlined, the track of the airliner, and failure to answer warnign calls on guard also came into play, but these are the basics.

[hazatude]

It's obviously a Decepticon laying in wait.

[BigglesNBella]

I heard ATC giving a traffic advisory for either a slow aircraft or ship near YYJ once. They were not sure what they where picking up.

Could have been me. YYJ tower has warned me of primary targets out near Active Pass twice now. Both times it was a BC ferry.

[Chuck Ellsworth]

Both times it was a BC ferry.

Some years ago I had Vancouver give me traffic at 12 o'clock and 2 miles opposite direction slow moving, I answered negative contact.

They then gave me the traffic still at 12 o'clock opposite direction slow moving...I answered negative contact it must be a B.C. ferry.

They said if it is it is squalking 1200.

[N181CS]

All "ships" that run in the Seaway system have transponders for seaway control and for other ships. Your Xpr show how far a head or behind and the speed that other ships are at in the seaway.

[iflyforpie]

Maybe there was a Beaver step-taxiing in the soup, oblivious to the CAVU conditions a mere 200ft up.