TCAS, Mode S and not hitting 'tinks' .....

[PH-UKU]

Genuine flight safety question for the low-level flyers out there ......

If I'm pootling around the Scottish lochs in a seaplane, with Mode S switched on, how likely is this to assist you in knowing I am there .. ?

I know that Tucanos have got some form of TCAS fitted, and also the larger Nimrods and Hercs etc.... so I am guessing they will get a TCAS alert ... ?

... but what about Tornadoes, Typhoons and the Americans ?

Would my Mode S be picked up on any RWR ? Or will it only be picked up if it is being interrogated by a ground-based radar ?

What about the Hawks or numerous heliocopeters - do any of them have Collision Detection systems ?

Would like to feel that the £3k I have just spent (at the CAAs behest) might actually be making my flight (and those around me) safer....

'tink' is what US controllers call Cessnas and Pipers ... cos seemingly that's the sound they make when they bounce off a Boeing or Airbus ... :hmm:

[gashman]

It isn't going to help unless the other jet has it too. That rules out the RAF front line fast jets. Not sure if it needs line of sight too? If it does, 2 low aircraft on other sides of a hill may not get any info on each other.

Using the normal modes of your transponder is different and is advised. Most platforms in NATO capable of firing air to air stores have an interrogator on board. This asks transponders if they are squawking, and some of them also ask what they are squawking. If ATC know you are about, a crew may interrogate an area and expect to get a reply back before the radar has enough information to build a useable track. Something about your kit transmitting a location rather than a radar pinging out in all directions hoping to hit something.

At low level, if you are using your eyes to avoid the ground, so is everyone else. TCAS would be unuseable unless you were transiting above safety altitude. ATC is at best info only, sometimes nothing at all, see and avoid and be well lit when you are below 500' on approach.

[spheroid]

RN Helicopters normally use the LOTFW principle. However, with the advent of Mode S this has become a little more tricky. However, the collision detection system in a Grey Seaking is extremely reliable.

[brit bus driver]

It isn't going to help unless the other jet has it too.

Not true. If the other ac has a transponder squawking regular Mode C, TCAS will still provide a TA/RA. The only difference is that it will not be a 2-way process, so the other traffic may be doing the same as you.

Having been attacked by Hawks ivo St Rumble and F-18s in the circuit (an RA on finals for an 'against the flow' circling approach is always fun!), I can vouch for this.:ouch:

[Spam_UK]

I know that Tucanos have got some form of TCAS fitted, and also the larger Nimrods and Hercs etc.... so I am guessing they will get a TCAS alert ... ?



Nimrod MR2 still don't have TCAS, or any warning systems other than the Mk 1 Eyeball, or an attentive ATC person.

[Not Long Here]

"Nimrod MR2 still don't have TCAS, or any warning systems other than the Mk 1 Eyeball, or an attentive ATC person."

So I guess the IFF Interrogator built into Searchwater doesn't count then?

[Brain Potter]

A Mode S transponder does not provide the traffic avoidance function per se, but is a necessary component of a complete ACAS II system. 2 aircraft with Mode S transponders, but no ACAS system will have no more direct protection from each other than aircraft with Mode A/C or no transponder. If one of the aircraft has an ACAS II system, it can generate a collision-avoiding Resolution Advisory for it's crew to follow. If both aircraft have an ACAS II system, the RA is co-ordinated by communciation between the 2 ACAS processors through the Mode S transponders.

The RA action is only the vertical plane; the azimuth information is much less reliable and is presented to aid visual aquistion rather than to cue lateral avoidance. Contrary to what has been posted, the system works below safety altitude, and can issue a "Descend" advisory depending on radio altitude. The radalt input disables the RA function automatically when close to the ground for take-off and landing.


PH-UKU,

Your Mode S transponder has been mandated by EASA, citing that it is essential for the effectiveness of ACAS on commercial air traffic. As BBD has described, the ACAS II system takes equally effective unilateral action against an "intruder" with either a Mode S or a basic Mode C transponder. I suspect that Mode S, rather than just Mode C, has been mandated because of the additional benefits of the Mode S Elementary Surveillance (ELS) function to ATC.

I don't think that any of the RAF fast-jets have an ACAS system. The Tucano has a form of ACAS I (no RA information) but the Herc does have a TCAS (I think), so keep squawking and heed all the old advice about lookout.

[US Herk]

USAF Hercules have TCAS - don't think USAF Fast Jets have it though.

[TheInquisitor]

All RAF Hercs have a TCAS fit. It will give you TA / RA on anything with a mode C transponder, as will any TCAS / ACAS II fit. FJ do NOT have it fitted, for the simple reason that the very high ROC / ROD commonly encountered in a FJ will give you RAs up the yin-yang, since the system is not designed to cope with it. Does that answer the question?

[Double Hush]

Au contraire! As long as you classify the new Hawk T2 as a FJ! Amongst some of its other gucci kit, it has ACAS II and has proved its worth, avoiding a 180x0 with a pair of (non-ACAS) low level Hawk T1s in Wales a few weeks back.

[Brain Potter]

Inquisitor,

An ACAS II equipped fast-jet may well get RAs caused by it's own high rates of climb and descent. Equally though, non-ACAS fast-jets squawking Mode C are unknowingly triggering RAs in other traffic, which is why they have been asked to limit their manoeuvres to 8000fpm when near controlled airspace.

An ACAS II fit in a front-line fast-jet would have it's full utility reduced by being set to 'TA Only' whenever the aircraft was operating as part of a formation, which would be most of the time.