"TCAS RA" Call

[Wornout Rubber]

Can someone explain the logic of making a "TCAS RA" call to ATC during a TCAS recovery?

A TCAS RA manoeuvre is a short time, high workload recovery. The PNF/PM should be giving his full monitoring capacity to ensure the PF is flying the TCAS RA recovery accurately. During the TCAS RA recovery the TCAS is the Air Traffic Controller, and all intructions from ATC must be ignored.

A call to ATC of "TCAS RA" is potentially dangerous, as it degradres the monitoring capacity of the PNF, may distract the PF and may invite a clearance from the ground controller which conflicts with the TCAS clearance. Confusion may result.

A safer and better procedure would be for radio silence during the TCAS RA manoeuvre, and a call made to ATC made only after the "Clear of Conflict" aural. This will ensure that both pilots can give their undivided attention to perform the TCAS RA manoeuvre accurately and without any unnecessary distractions.

[Tarq57]

Can someone explain the logic of making a "TCAS RA" call to ATC during a TCAS recovery?

In a nutshell, it's so the controller is then aware that the aircraft he/she may have been expecting to do one thing is in fact likely to be doing something else. This might then "save the day" vs other traffic the controller might have been about to clear for a descent/climb into the area of conflict.
(Example in English: If we see an aircraft has descended through level X, another aircraft above can then be cleared to descend to the level just vacated by the one below. If the lower one then starts to climb in response to an RA, there is no separation. Of course, a subsequent RA, or even a series of them, is likely.)

The other big reason, is that if the controller notices an aircraft climbing when it should be descending (for example) and observes a potential loss of separation about to occur, control instructions - perhaps quite agitated control instructions - will continue to be passed.
Making that call should ensure that the controller knows to immediately stop controlling the event. Without that call, the controller will/should keep attempting to provide separation.
(In practice, it takes a bit of conscious will power to "butt out". Goes against all prior training. That's probably part of the reason there are quite a lot of anecdotal reports of "butting-out" not really happening.)

[n5296s]

Flying a VFR transition through the San Francisco Class B (which for all practical purposes means you are flying under IFR, as far as interactions with ATC are concerned) a while back, I was visual with an airliner and he called to say he had an RA (which was obviously me). He sounded annoyed but didn't change course - there was no risk since he was at my 11 o'clock and flying to my left, and climbing fast. I don't know how an RA works when one of the aircraft isn't TCAS equipped (I just have Mode S).

n5296s

[AltFlaps]

If ou didn't have TCAS, then it wasn't an RA ... most likely he got a 'Traffic' call

[Tarq57]

A TCAS equipped aircraft will still get an RA from a non TCAS equipped aircraft. All that is required is an operable mode C (or better) transponder. The only difference is that it will not coordinate a response with the other aircraft.

[muduckace]

The only resolution authority I have not experienced but have second hand information had resulted in structural damage to the horizontal stab of a DC10-30. There is no time (and should not be considered) to contact ATC until the RA has been performed, this was at cruise over Columbia.

High altitude reporting over countries that still allow communications other than English contribute to this. FANS is supposed to be the solution.

None the less TCAS is vital as the priority to allow a reactive solution, communication falls second as a proactive and safer method to avoid airborne collision.

[llondel]

Surely they're missing a trick here - if the TCAS system can tell the pilots of affected aircraft, it shouldn't be too hard to have it notify ATC. Of course, cost of modification is probably the limit, especially if there's not much evidence of accidents caused by TCAS RA and ATC conflicting. I can only think of one offhand, but that was ultimately a pilot training issue where the pilot followed ATC when instructions from the TCAS said something different. Adapting the squawk would be an obvious mod, then there would be immediate visual on the ATC radar that an aircraft was doing its own thing. However, $$$ is always going to be the issue.

[Dani]

and I know a story to tell, in which some 70 people still would be alive if one of the two crews would have reported what they are doing. They both descended, one ordered by ATC, the other by ACAS (TCAS), until they hit each other. The place was Überlingen, Germany, in 2002.

[Tarq57]

Adapting the squawk would be an obvious mod

I've for some time wondered how straightforward it would be to have a transponder automatically squawk something from the 7000 series when an RA is triggered.
And whether this would in fact be a good (at least short term) solution, or if it would present more problems.
Sometimes simple is best.
I suspect that getting everyone to consider and agree to such an idea might be a larger hurdle than the tech aspects.

[llondel]

some 70 people still would be alive if one of the two crews would have reported what they are doing. They both descended, one ordered by ATC, the other by ACAS (TCAS)

That's the one to which I was referring. Had they both done what TCAS told them, there wouldn't have been a problem, no need to tell ATC their intentions. However, one crew was trained to obey TCAS in case of conflict with ATC, the other was trained to obey ATC. Now they're all trained to follow TCAS, so they shouldn't collide with the other aircraft involved. Of course, that doesn't stop a secondary alert being triggered as they move into conflict with other traffic.

[hollingworthp]

It takes hardly any time to transmit the "TCAS RA" message on the current frequency while monitoring and assisting the PF and as posted above, 'helps' to reduce RT from ATC during the manoeuvre.

[falconer1]

the new Mode S TXPs

installed in 99.9% of the air transport fleet nowadays could in fact already transmit data downwards to the controller that two aircraft are in a TCAS RA situation, making any verbal comms by the crews redundant and unnecessary..that's not the problem..

problem is, at least in Europe that Eurocontrol has not updated the groundstations here to be fully compatible with what 99,9% of the aircraft already can do..

Why?? every country still has different software and despite charging huge Nav Fess, those fees are not correctly spent by our European politicos..

so in most aircraft all that would be needed is some restrapping of on the transponder connectors, if at all.. doesn't cost a thing..

but unfortunately useless unless ATC updates their equipment

[Denti]

Mode S is a standard part of every ACAS II installation as that is required to provide the datalink channel for coordinated manouvers. And that sends out a RA alert mesage which could be displayed on the controllers screen, but sadly is not in most installations.

I do not know how all over europe the mode-s ground infrastructure is at the moment, however it seems that the local ATC provider are working on implementing mode s into their infrastructure. In germany all radar sites have been upgraded to be mode s compliant, however most of the mode s data is not used and displayed to the controller. At the moment only the Flight ID tag is displayed as far as i know. The official reason is that as long as the flight ID still shows a failure rate of more than 1% (most of it crew-induced) it has to be assumed that the other data is invalid as well and therefore cannot be used.

[Dani]

Quote by IGh:
There were at least two fatal RA-induced upsets

If they really did that, it's not the fault of TCAS. TCAS evasive maneuver do not call for abrupt procedure. In fact, TCAS reactive procedure are very smooth, you deviate from the original altitude only a little. Lateral maneuvers are not required.

But you can abuse every system. Those pilots didn't do their job correctly.

Anyway, what has it to do with the topic? It's about calling ATC.

Dani

[Rainboe]

There is plenty of time for an ATC call to alert ATC and other traffic that a RA is ongoing. The manouevre is gentle and easy. It doesn't matter what speed or altitude is used, the response is easy and can be monitored whilst the manouevre is taking place. It's not a problem.

[Flare-Idle]

TCAS RA and Structural Overload

Regarding structural overload risks of TCAS/ACAS RA maneuvers :

Initial RA command requires 1500 ft/min climb/descent to be reached within 5 seconds with max pitch g-load of +1.25g or +0.75g. If subsequently more progressive RA action required 2500ft/min to be reached within 2.5sec with loads of +1.35g or +0.65g. Far away from limit load of +2.56g or -1.0g, if you follow the VS command correctly. On HUGS equipped aircraft TCAS/ACAS RA maneuvers more easy to follow since Fly-To-Box displayed on the combiner...

Cheers

FI

[Denti]

Dave Learmount recently talked in his blog about airbus developing an additional autopilot mode that will execute RAs on its own. Background for that is that many RA manouvers are flown with exessive (sp?) control inputs.

[lalbak]

I agree with Rainboe, there is enough time to make a simple "TCAS climb/descent" call while monitoring the PF. Even if you miss the ATC response who cares, you will follow the RA despite ATC instructions. In my experience ATC won't give you any instructions until you call "clear of conflict" anyway...

[Graybeard]

Creeping Socialism

Back when TCAS was developed, pilots were insistent that the TCAS not be a command, but an advisory, hence, Resolution Advisories and not Resolution Commands. Now you say it's going to be automatic. Uh, oh; Big Brother is taking over.
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I was involved with an accident investigation in which an FA was injured. The 757 was at 18,000 feet on descent when ATC alerted the pilots to oncoming military traffic 1,000 feet below. TCAS then issued a TA, which was followed by "Whoop, whoop, Pull Up!" The startled pilot hauled back on the yoke and dumped the FA.

TCAS was not at fault. The #1 Radio Altimeter momentarily sensed the fighter below, and ran its indicated altitude down to 1,000 feet. The GPWS jumped on that and issued the Pull Up.

Sundstrand had issued an optional service bulletin to add some filtering to the GPWS warnings, which would have avoided the incident, but the airline had a policy of refusing to pay for optional bulletins.

GB

[Spodman]

I've for some time wondered how straightforward it would be to have a transponder automatically squawk something from the 7000 series when an RA is triggered.

This would mean the controller would lose positive identification of which aeroplane is which in the situation at a fairly critical time. Dumb idea.

In both the TCAS RA I have been involved in I was able to reassure the pilot there were no aircraft anywhere near him (that I knew of anyway). If there had been another I could have passed the traffic, which could help ensure a coordinated response, or I could have passed a reacting pilot traffic on a third aircraft his reaction has compromised separation with, or even arrange separation with that third aircraft.