TCAS safe for ATC?
 

:confused:

Acft transmits blind on ATC freq that head-on traffic as same level. ATC descent the aircraft to a lower level. Opposite traffic calls thereafter that it already iniated TCAS desent. What know? Has any recommendation regarding the use of TCAS after the Ueberlingen accident been adressed already?

Should've been adressed after the incident in Japan (January 2001) already...

http://aviation-safety.net/database/2001/010131-2.htm

From the report:

The commission recommended a.o. that the International Civil Aviation Organization (ICAO) put priority on computer orders over instructions from controllers to prevent similar incidents.

1.5 years later Ueberlingen happened...

In the US from the very onset of TCAS, ATC has in our rule books that we NOT intervene as soon as we know that a TCAS RA is taking place. We do issue traffic but we don't do anything else until the aircraft advises that they are finished with the TCAS event.

regards

Scott

Of course we only know of a TCAS RA by pilot reports. The controller will be ignorant of an RA for at least 5-10 seconds and possibly up to 20 or more seconds, that's plenty of time to issue an instruction which may be opposite to TCAS.

There seems to be more of a tendancy to give avoiding action in the horizontal plane only now, but will pilots follow this advice when a bank angle of more than 5 degrees can cause errors in TCAS ?

In the original question the "other" ac has taken the RA, so the pilot of "our" aircraft must be getting an RA and should therefore disregard ATC level instructions and follow the RA.

At least that's what I think!!!

Also, if a pilot reports an RA I will always give traffic info and, IF I THINK IT IS RELEVANT, avoiding action in the horizontal plane only...

Usually yes Barry. The other aircraft would indeed also receive an RA, and in most western companies that RA will take priority over any ATC instructions.

However, if the other aircraft has no TCAS (fortunately more and more rare nowadays), but only a mode-C transponder? 'Our' aircraft will create an RA based on the current vertical behaviour of the other aircraft. If ATC now issues an instruction to the other aircraft opposite to what it was doing it could at least cause a problem with the RA instruction. It may be revised to a more aggressive manouvre, or of course it could be worse...

TCAS resolutions are supposedly confined to the vertical plane; for this reason it might be better to limit ATC instructions to turns - of course you may only make matters worse, depending on the radar resolution - or better still to only give traffic info.

I can safely say that I would not follow any advice from anybody until the TCAS RA is over, you don't even do what your eyes tell you, the aircraft you see might not be one the generating the RA.

Actually, it is my experience that TCAS RA's are announced just about immediately over here...

regards

Scott

Scott, how can you know that ? You'd have to be on the aircraft and hear the RA to know for sure.

The reason I mentioned the delay in reporting an RA is the tragic Lake Constance example when there was a delay in the DHL RA report. I don't mean to lay any blame, just to show an example of the pilots' first priority to aviate and navigate before communicating an RA.
In an ideal world one pilot would fly the RA and the other announce it immediately. In the real world a delay of 5-20 seconds doesn't seem unreasonable.


Max Angle said

Is that what we might expect all pilots to do ? Are ATCO's training for this ? Is it worth giving any avoiding action during an RA incident ?

Here's the FAA 7110.65:

2-1-27. TCAS RESOLUTION ADVISORIES

a. When an aircraft under your control jurisdiction informs you that it is responding to a TCAS Resolution Advisory (RA), do not issue control instructions that are contrary to the RA procedure that a crew member has advised you that they are executing. Provide safety alerts regarding terrain or obstructions and traffic advisories for the aircraft responding to the RA and all other aircraft under your control jurisdiction, as appropriate.

b. Unless advised by other aircraft that they are also responding to a TCAS RA, do not assume that other aircraft in the proximity of the responding aircraft are involved in the RA maneuver or are aware of the responding aircraft's intended maneuvers. Continue to provide control instructions, safety alerts, and traffic advisories as appropriate to such aircraft.

c. Once the responding aircraft has begun a maneuver in response to an RA, the controller is not responsible for providing standard separation between the aircraft that is responding to an RA and any other aircraft, airspace, terrain or obstructions. Responsibility for standard separation resumes when one of the following conditions are met:

1. The responding aircraft has returned to its assigned altitude, or

2. A crew member informs you that the TCAS maneuver is completed and you observe that standard separation has been reestablished, or

3. The responding aircraft has executed an alternate clearance and you observe that standard separation has been reestablished.

NOTE-
1. AC 120-55A, Air Carrier Operational Approval and Use of TCAS II, suggests pilots use the following phraseology to notify controllers during TCAS events. When a TCAS RA may affect an ATC clearance, inform ATC when beginning the maneuver, or as soon as workload permits.

EXAMPLE-
1. "New York Center, United 321, TCAS climb."

NOTE-
2. When the RA has been resolved, the flight crew should advise ATC they are returning to their previously assigned clearance or subsequent amended clearance.

EXAMPLE-
2. "New York Center, United 321, clear of conflict, returning to assigned altitude."

----------------------------------

Once again, the danger lies in the lack of standardization around the world. For something a critical as TCAS/ACAS RA's, we very much need to be on the same page.


ATC 24/7

Regarding how ATC respond to TCAS RA's it is 'good practice' not to give any vertical avoiding action once an RA is notified. (Having said that, in the proverbial heat of the situation I'm sure some controllers may try to climb/descend an a/c back to where they thought it should've been.

Traffic information is encouraged but we're encouraged only to give avoiding action in the horizontal plane and wait until you report 'back under my control'.

"You'd have to be on the aircraft and hear the RA to know for sure"



We as pilots are of course trained to respond to RA's. We also are aware a response may cause us to deviate from altitude and the relative comfort that an assigned altitude provides. It only takes one guy to handfly the escape maneuver, the other is taught to immediately advise ATC so they are in the loop. Many times a RA is not a great surprise. Watching the TCAS we see someone heading towards us, it turn to a TA and finally a RA. This allows time to think about impending requirements such as ATC notification.

Del;

What West Coast said, also I have been both in the sims watching the training as well as in the jump seat (back when we could) and have watched it first hand (With VFR's who were 500 feet away, which by the way is perfect separation.). Also we can see that the aircraft hasn't even started the manuver yet when they report the RA... It's a training thing here that we started at the onset... One of the nice things of having ONE aviation authority for a LARGE bit of airspace <G>...

regards

Scott

Pilots will normally advise ATC of RA immediately. That is the job of PNF. In the DHL accident from recollection, one of the pilots were out of the seat (had just gone to the toilet), so the SOP of PF performing the manoeuvre and PNF advising ATC of RA was flawed. The PF did what he was trained to do but there was nobody in the other seat to report the RA. It is a damning indictment of the aviation training setup. We practice standard "abnormals & emergencies" but never seem to think outside of the box.

Standardise procedures - worldwide
 

ATCEA.com - the need to standardise ATM procedures worldwide is possibly the most safety critical aspect we need to undertake at this time - urgently. ICAO set the standard which almost all countries have signed up to.

Eurocontrol (representing 41 European States) are working very hard on this aspect, in all areas of ATM. See eurocontrol.int/acas/ and go to the Bulletin pages for more info. Some good stuff there, based on the ICAO provisions.

One example: "One of the main messages for pilots to note from the ACAS training material is an emphasis on the need for pilots to ‘follow the RA’. Indeed, ICAO Doc.8168, ‘Procedures for Air Navigation Services – Aircraft Operations (PANS-OPS)’, Volume 1, Part VIII, Chapter 3, Paragraph 3.2 c) 1) of Amendment 12, states that: "in the event of an RA [Resolution Advisory], pilots shall respond immediately by following the RA as indicated, unless doing so would jeopardise the safety of the aeroplane".

Now wouldn't it be nice if the same could be said for the FAA, where they could standardise phraseology aspects on the other big issue, Runway Incursions, and move from "taxi into position and hold" to the ICAO parlance of "line up and wait". Everyone can be a winner.

Where theres hope.......:ok:

Blue, thanks for the references. Your reply is both thoughtful and informative.

I agree the the US and the FAA are often the "culprits" in the efforts to standardize precedures. For many years, I believe our attitude has been, "We're the Big Boys - you wanna play, you play by our rules!"

Slowly but surely, that attitude is changing for the better. A good example is the FAA's acceptence of ICAO METAR and Airspace Classification procedures. I agree, however, we have a way to go yet.

ATC 24/7

Ok, to throw the bomb out there, just what is wrong with "position and hold." vrs Line up and wait???? Don't say just cause that is ICAO. That doesn't hold water with me. ICAO makes changes, just like that stupid one not so long about on changing to taxi to holding position.... Looks to me like they CAUSED more of a problem.

regards

Scott

Prepare for thread liftoff...

tcas ra's
 

I was working two days ago. Had two a/c, one climbing, one descending, nose to nose, with 1000 ft. vertical assigned ( the right way) and acknowledged. Passed traffic to both a/c. When a/c were approx. 5nm nose to nose, descending a/c, about 300 ft above cleared level, had an RA.
He announced TCAS climb, but only climbed about 100 ft, before announcing he was resuming ATC cleareance. The opposite direction climbing a/c did not get an RA. Climbing a/c was within 200 ft. of his cleared level.

I have been told by pilots, and assumed, when traffic is passed in similar cases, pilots decrease their vertical rates to avoid RA's.