Avoidable TCAS RAs ?
 

Picture this. Commercial aircraft cruising at FL180. Base of CAS FL175. As far as I'm aware (in this case) aircraft can safely cross at FL175 without any separation implications. (Perhaps there are other caveats to that please corret me if wrong).
I am concerned, however that particularly military aircraft are within their rights to execute a rapid climb to a level 500ft beneath a commercial aircraft in these circumstances causing a TCAS RA which has the potential (however unlikely) to injure (or worse) those on board the passenger aircraft. Although common sense may tell you not to execute such a manoeuvre beneath a passenger aircraft, it does happen. Is this a problem ? Perhaps I'm overreacting. It wouldn't be the first time :}.
Any thoughts ?

P.S. (Chewbydoo ? There you go. Now you can explain your bizarre answer previously because I have absolutely no idea what point you were trying to make. Perhaps you misunderstood the question initially).

When assigning climb and descent at once to two aircraft dircetly over and below eachother, I will always teel them about the other for this reason. I am aware that in some areas in my Centre, the controllers assign 2000ft between in this situation. When you are talking 500ft, an RA is going to occur with any rate of closure anyway. No cure for stupidity.

Seem to remember reading somewhere that TCAS II went for a miss distance of between 500 and 700ft, so conflicting traffic could be 200ft outside CAS in level flight and still trigger TCAS. Almost certain that manoeuvring traffic is not allowed to use the base level of an airway (if expressed as a flight level).

3.142

Thanks for the replies guys.
Tobzalp - I'm talking about 1 aircraft (on freq) cruising in CAS and 2xmil aircraft (not on freq) playing maverick outside CAS.
The last radar recorded FL on the (2x Mil aircraft) was 173. (Although given rate of climb before mode c er....disappeared I wouldn't be surprised if they didn't climb a little more). I have been told that the mil aircraft were perfectly within their rights to do this. That I accept although I really thought it had to be at a right angle and surely not a good idea to 'attack' a civil aircraft (head on) when you know you are close to CAS. Some of the older boys in ATC feel it's not a problem - this happens all the time outside CAS. My problem is though, it WAS CAS. It seems to me to be, at the very least, foolish and at worst downright dangerous. Let's be fair TCAS RA to a mil aircraft is a flick of the wrist with pilot happily strapped in a 5 point harness. It's slightly different for Mr and Mrs Jones stood up in the cabin of a passenger plane with nothing strapping them to the airframe.

Have seen this problem where mil a/c working below CAS have taken a climb of 8000ft pm+ and although have levelled off well below CAS it has initiated an RA from GAT on route due to ROC. :sad:

I don't think you can manoevre at the base level; I believe you may cross at the base level in VMC.
I've never heard of this causing a problem, but i suppose, theoretically it could.

I have official feedback which states that the mil aircraft was operating within the rules. Perhaps due to the highest recorded level being 200 ft below the base level, however the addition to the feedback was that aircraft CAN operate at the base level at right angles - but these aircraft were flying down the centreline of the airway head on to the GAT so I don't understand that point. Oh well, thanks again for the replies. This is just another area of ATC where an injection of a little common sense would work nicely but that doesn't seem possible. The interface between mil and civil seems a little lacking at times. We share these problems, appreciate each others difficulties in the working environment and then nothing useful seems to be done to remedy the situation.

Few years ago whilst I was working at Scottish we had a civil cruising at FL290 and military coordinated DA20 climbing to FL280. The DA20 climbed quickly which set off the civil TCAS and the pilot reacted IAW the RA. DA20 leveled as cleared at FL280. Still made a splash in the papers even though everything was done correctly :ooh:

BD

Are you sure these aircraft were working military ATC?

BD

TCAS....
 

good question......cant talk for the higher levels but it causes problems closer to the ground!

i frequently have to stop aircraft off at 3.5A as there is VFR traffic well within their rights flying outside CAS at 2.4A.

just saves the paperwork....

BDiONU I am fairly certain that they were under military control in 1 of the north sea training areas. I say 'fairly certain' because I'm thinking back to about 2 months ago and although I'm pretty damn sure about it I don't want to misrepresent the people involved if I've remembered incorrectly the report. (Infact, I'm adding this after, I remember the mil bod calling my coordinator about it (and being a little defensive too)).

126.825, despite the fact that I can legitimately have traffic at the lowest flight level I do take your point about added caution. Belt and braces, etc and why not! Like you say, saves us filling forms in ! Unfortunately I think that in the airspace in question, the bases are so high that some companies may push their aircraft types just up into CAS just to receive a better service. Even more reason to make damn sure they get that service to my mind !

By 'military control' do you mean ATC or Air Defence because the two are very different. The interface between Mil ATC and civil ATC is generally very good. However its often very difficult to coordinate with air defence, particularly if the aircraft causing you a problem are being controlled by AWACS.

BD

The scenario is just one of those things. Aircraft operating below the base are deemed to be outside controlled airspace and separation is therefore 'assumed' from anything within. Note that it does not have to be to the same degree as you would provide between 2 IFR aircraft under your control. They are separated as deemed by the authorities, who presumably would carry the can if there is a nasty as a result.

I agree with your comments Pprune Radar but I also think these acceptable separations were deemed acceptable before TCAS was established. TCAS as we have all seen in many different scenarios can add major complications in certain circumstances as well as add a very useful safety barrier. Perhaps the authorities should have another look at these things. It's always small, seemingly insignificant things that cock us up in this game.
(BD - I think it was MIL ATC that we are often in contact with but I can't remember exactly.. My point was that I think we have good relations but not a lot seems to come from observations made.)

Cheers for your thoughts guys....
:ok:

Would the U/T that posted and then possibly removed post please recontact me out of interest. Ta. (I was par terre btw).