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TCAS procedures
My company which flys aircraft from 3 different manufacturers all include in the respective TCAS procedures elements of the pilots looking out to visually identify the intruder aircraft....
my simple questions is "why do we bother doing this?" The TCAS alerts the crew, and if a RA occurs, one takes the appropriate vertical deviation as generated by the TCAS unit. Who cares where the aircraft appears (if the crew can see it all) and of course you would never ignore a TCAS just because you can see the intruder aircraft. So for procedure simplification's sake why don't we just wait for an RA and if it happens, follow it. Procedure done. All this nonsense about adjusting ND scales etc, PNF looking seem to take our attention away from the primary and only important step of maneuvering the aircraft vertically. Are there some certification requirements from the early days of TCAS II that required the crew to attempt to visually acquire the other aircraft?? thanks in advance. 767-300ER |
It's called Spatial Awareness and good airmanship!
A good look out is thrust upon us all (or at least should be) from a very early stage in training. In a commercial environment a good look out should be adhered to aswell IMHO! Why: Climbing at a 'good rate'! - many contacts in your vicinity, always a good idea to observe TCAS and outside to gauge where, what, when etc... Military Trafffic! - You may not observe the military guy on TCAS:E, but a good eyball and help from ATC may help you in your decisoin making process. GA aircraft, especially on departures and arrivals into airfields with both GA and commercial operations. Wake Turbulance! - A good eyeball can tell you to reduce your ROC, ROD to avoid possible wake etc.. Visual Approaches! - self explanatory me thinks!!! Probably lots more reasons to keep an eye on what's happening outside, but obviously you must observe your TCAS and what it's telling you should you get an RA. Oh, TCAS RA phraesology has changed too: CHANGES TO ICAO RULES REGARDING TCAS RAs (as of 22 Nov. 07) By Stanislaw Drozdowski Stanislaw Drozdowski is an ATM Expert at EUROCONTROL HQ in Brussels, working in the area of ground and airborne safety nets. Previously, he worked as a system engineer with Northrop Grumman and as an Air Traffic Controller in Poland and New Zealand. In the last issue of HindSight, in my article about TCAS and STCA (see TCAS and STCA - not just anagrams, HindSight 5, July 2007, page 19) I remarked that ICAO rules concerning RA reporting would change in the near future. ICAO has now published the changes that will become applicable on 22 November 2007. Below is the summary of the changes to ICAO PANS-ATM (Doc 4444) and ICAO PANS-OPS (Doc 8168). PHRASEOLOGY The first change concerns the RA report phraseology. The new phraseology is: “TCAS RA” The controller response to the RA report is an acknowledgement (“Roger”). This change was implemented to simplify RA reporting. Previously, pilots were required to include the direction of the movement in their RA report (i.e. “TCAS Climb” or “TCAS Descend”). That sometimes led to ambiguous situations as no phraseology existed to report the most common RAs (Adjust Vertical Speed) and pilots often improvised their reports creating extra confusion in the situation that was already stressful for the controller. For example, an “Adjust vertical speed” RAs calling for the reduction of the climb rate due to another aircraft above were sometimes reported as “TCAS Climb”. In fact the aircraft was still climbing but at a lower rate. That gave the controller a false indication that the TCAS resolution was telling the pilot to continue the climb towards the other aircraft. That caused, in some cases, the controller to issue an instruction during the RA, resulting in confusion at the flight deck and prolonged radio exchanges. On the other hand, the controllers should note, that the new phraseology may limit their awareness as to the direction of the movement of the aircraft responding to the RA. The pilots are now required to explicitly announce the TCAS “Clear of conflict” message when the conflict is over: “CLEAR OF CONFLICT, RETURNING TO (assigned clearance)” or “CLEAR OF CONFLICT, (assigned clearance) RESUMED” The controller response to the “Clear of Conflict” report is an acknowledgement (“Roger”) or provision of an alternative instruction. The clear indication of RA termination will now allow the controller to recognize when the RA is completed and when he/she can start issuing clearances or instructions to the affected aircraft. In the event that the controller issued a clearance or instruction contradictory to the TCAS RA, the flight crew will follow the RA and inform the controller: “UNABLE, TCAS RA” The controller response to that RA report is an acknowledgement (“Roger”). Previously, the “unable” phraseology included the direction of the RA (e.g. “Unable, TCAS climb”) – this change is in line with the RA reporting changes as described above. WHICH RAs MUST BE REPORTED? The second significant change concerns the types of RAs that must be reported. Previously, the pilots were required to report all RAs to ATC. With the change applicable on 22 November 2007 the pilots will report only those RAs that require a deviation from the current ATC clearance or instruction (“As soon as possible, as permitted by flight crew workload [the pilots shall] notify the appropriate ATC unit of any RA which requires a deviation from the current air traffic control instruction or clearance”). This change should eliminate reports of RAs that are not significant for ATC, i.e. those not leading to deviation from the current clearance. That should cover the majority of RAs issued to the fast climb or descending aircraft approaching their cleared level while another aircraft is immediately above/below. ICAO believed that these reports cause unnecessary workload for the flight crews and for ATC and, therefore, excluded them from the reporting requirement. It should be noted that in some cases pilots may have difficulty to determine whether the RA is requiring a deviation from the current ATC clearance. WHEN DOES THE CONTROLLER CEASE TO BE RESPONSIBLE? A change has been made clarifying the controller responsibility during an RA. Now, the defining moment when the controller ceases to be responsible is the departure from clearance or pilot report of an RA. The amended paragraph 15.7.3.3 now reads: “Once an aircraft departs from its ATC clearance or instruction in compliance with an RA, or a pilot reports an RA, the controller ceases to be responsible for providing separation between that aircraft and any other aircraft affected as a direct consequence of the manoeuvre induced by the RA. The controller shall resume responsibility for providing separation for all the affected aircraft when: a) the controller acknowledges a report from the flight crew that the aircraft has resumed the current clearance; or b) the controller acknowledges a report from the flight crew that the aircraft is resuming the current clearance and issues an alternative clearance which is acknowledged by the flight crew.” PROVISION OF TRAFFIC INFORMATION Until now, controllers were required to provide traffic information to the aircraft responding to the RA. This requirement has been removed as it is believed that at that point ATC traffic information provides little added value to the flight crew and might be distracting. Moreover, traffic information may be inadvertently inaccurate as the position and altitude information are delayed in surveillance processing. In some case controllers found issuing traffic information difficult due to the proximity or overlap of the aircraft labels and symbols on the screen. Also, traffic information and the visual acquisition of the intruder could prompt the pilots to stop responding to the RA. The amended paragraph 15.7.3.2 reads as follows: “When a pilot reports an ACAS resolution advisory (RA), the controller shall not attempt to modify the aircraft flight path until the pilot reports “Clear of Conflict”. Note – the most important principle of this paragraph remains in force – once an RA has been reported, the controller shall not attempt to modify the aircraft flight path, until the pilot announces “Clear of Conflict”. |
If the threat's transponder is switched off/becomes US, or stops reporting altitude then there will be no RA despite the fact that you might be on a collision course - you will then need to rely on see-and-avoid which will be a lot easier if you are already visual with the threat.
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767-300,
I agree. The first priority must be to get be ready to follow any RA accurately, and that means both crew, to make sure it is done correctly. Get your finger on the AP disconnect button and think about how much (or little) you are going to pull or push when bitching Betty squawks. Peering out the windows looking for an aeroplane that in a busy piece of sky may well not be the one causing the problem should be secondary. That said, fellman does raise a valid although probably less-likely scenario. |
I think CAT1 REVERSION's first point is important. Experience has shown that, despite how simple it sounds, there are many incidences (and at least one accident) where RAs aren't followed properly. There are a number of EUROCONTROL papers, I think from the same series as posted, detailing mistakes that were made. A concern is people overshooting the green zone and causing another conflict with somebody else.
Acquiring the target visually gives the pilot a spatial picture of the situation, with ranges and bearings, so that the pilot is in the same mindset as TCAS, which probably leads to more confidence in the RA, and better execution. Current traffic displays are bad at this: a 2-D snapshot picture of a inherently 3-D plus time conflict. Also, check out the new Airbus auto-TCAS system, which got recently certified. |
The reason the RAs don't work is because pilots don't follow them. The Russians got it completely wrong. Simple. In my opinion having pilots trying to second-guess or outwit the TCAS by attempting to dodge other aircraft visually should be left to fighter pilots. You have no idea what the other pilot might do during an encounter that will, in all probability, be over in a few seconds. We don't have time to visually assess the appropriateness of a RA and then do it.
Leave it to the TCAS. As for overshooting the VS during an RA, that's training. In a typical jet at typical speeds and levels, 1° of pitch attitude change will result in a VS change equal to your Mach No x 1000. If you're doing Mach 0.7, 1° will result in about 700fpm VS change. Not very much pitch change is required to comply with a VS RA (and you have 5 secs to achieve it). Practice it in the SIM. Your life may depend on it one day. |
767-300ER . . . you're going to get a "traffic" alert before any "RA," and getting a "traffic" alert in itself may not even result in a "RA" . . . so there's nothing wrong with first looking outside; it's an instinctive reaction by most pilots. Not you? :ooh:
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767-300ER . . . you're going to get a "traffic" alert before any "RA," and getting a "traffic" alert in itself may not even result in a "RA" . . . so there's nothing wrong with first looking outside; it's an instinctive reaction by most pilots. Not you? http://images.ibsrv.net/ibsrv/res/sr...ies/icon25.gif 100% RIGHT.... Airmanship, Airmanship, Airmanship. the basics are fast becoming a thing of the past. It's unbelievable how many posts I read where automation and apathy result in confusion and incidents:eek:! Of course you follow your TCAS, thats what we are trained to do, but are you telling me 767-300ER, you want to just sit in your seat heads in and ignore outside visual cues that could save you from having to perform an RA manouvre? Rubbish......Get your eyes out and have a look if it's an alert, if it worsens to an RA, different ball game, you have to be heads in. Answer to your original question, No I don't think we should just wait for the RA and follow it if a good visual can avoid it in the first instance, and I'm sure your training department would advise the same!!!! Goodness me, are some Pilots getting that lazy????? |
767-300ER,
I take your post as a clear example of the level of negative training that has come along with the invention of TCAS. Your basic contention is that your primary means of avoiding a collision is "Sit, wait, and follow the RA" TCAS is a last ditch, emergency system that escalates to RA mode after giving you several cues that things are not as they should be. Aquisition of potential collision traffic during proximat phase or, as a final chance, TA phase and maneuvering to avoid an RA is surley much preferable to putting you and your passengers lives in the hands of a last ditch maneuvre that will provide 1-200ft seperation IF both pilots respond to the RA correctly. If we miss a staionary mountain by 200ft, we call it a very close call, yet you seem content to allow an automated system to guide you to a very small seperation from an object with which you have 900kts closure. Should we "Wait and prepare ourselves for the Terrain Avoidence maneuvre once we get an EGPWS warning", or keep clear of terrain without ever setting it off? Try this next time you are in the Sim- While your partner is flying, flick your TCAS to TA only (which is the only alert you recieve if the target aircraft is only squawking mode A), and watch as he patiently waits for the RA that never comes to save him. Don't get me wrong- if it get's down to an RA, the RA guidence should be followed by SOP, but there is NOTHING in TCAS procedure that stops you visually aquiring and avoiding a possible collision before it ever gets as close as an RA. You have no idea what the other pilot might do It is still enshrined in international air law that two aircraft on a collision course shall both alter heading to the right. |
but there is NOTHING in TCAS procedure that stops you visually aquiring and avoiding a possible collision before it ever gets as close as an RA. I'd guess about 0.0000001% Unless you're a trained Air Force fast air pilot with interception skills I doubt a pilot can accurately gauge a collision risk. If every time a pilot looked out and saw an aircraft that looked like it was at co-altitude and risking a collision course and reacted as suggested, there would be aircraft climbing and diving all over the skies. No I am not "contending" that we sit back and wait for TCAS...but again, with 900 kts of closure for two aircraft approaching head-on, please explain how long the average pilot has to: a/ see the the traffic b/ determine whether there is a collision risk, and c/ make an appropriate maneuver to avoid this collision (all being done visually). |
B767,
We see a target on the TCAS go from interest to proximate. It is at 1 o'clock by the display, with a constant relative bearing and showing an altitude deviation of zero. As we look out the window, the target turns yellow and a "Traffic Traffic " is anouinced. We see an aircraft contrail 8 miles away We now have 30-45 seconds to PCA, knowlwdge of where the target is, and can be sure it is at our level. Do you sit, wait, and follow the inevitable RA, or initiate a right turn which will give you much more clearence, and still leave you able to follow a subsequent RA should it occur? Out of interest, what does your manual state as SOP for a T/A? Everyone I have read says "Attempt to aquire tartget visually and maneouve as required". The fact that most pilots DON'T attempt to avoid the RA is, as I stated, the result of negative training as simulator senerios artificially produce RAs (by, usually, ALWAYS occuring in IMC) in order to train the RA maneouvre, without stressing that in the real world, there are opertunities to ensure avoidence before it gets to that last, emergency manoeuvre. |
Wiz,
Out of interest, what does your manual state as SOP for a T/A? Everyone I have read says "Attempt to aquire tartget visually and maneouve as required". Maneuvers based solely on a TA may result in reduced separation and are not recommended. As for your scenario, have a read of event 4 in this document: http://www.arinc.com/downloads/tcas/...our%20JULY.pdf That could well happen to you when the other pilots spot you and do a similar dodgem manoeuvre. As for correctly giving way to another aircraft at 900kts closure and with only a few seconds to visually acquire the other aircraft, "your ego's writing cheques your body can't cash". ;) |
You obviously don't fly Boeing 737s because the FCTM says: Maneuvers based solely on a TA may result in reduced separation and are not recommended. Look for traffic using traffic display as a guide. Call out any conflicting traffic If traffic is sighted, maneuver if needed. |
NEVER attempt to fly an avoidance manoeuvre based purely on a TA unless you are 500% confident that you have visual contact with the traffic that has caused the TA, and an actual risk of collision exists.
Wait for the RA and fly the vertical solution that is generated. Also be aware that TCAS azimuth information on the VSI is not 100% reliable. Your `home made` avoidance turn in response to a TA or perceived interpretation of proximity traffic azimuth info COULD WELL MAKE THINGS WORSE! |
Manueuver is not needed until you get an RA...
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You can never be sure what you've acquired visually is what caused the TA/RA.
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Why not look out the window and if you see the traffic, turn to avoid conflict rather than just follow the green on the TCAS. Remember TCAS only controls vertical separation. Why not have both vertical and lateral separation? Blind faith in the TCAS might not always work. Follow the green but turn too for insurance if you see the suspected conflict.
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Follow the green but turn too for insurance if you see the suspected conflict. Wiz, read your FTCM on TA response. |
CB, I don't think bank has anything to do with TCAS. TCAS gives alerts based only on altitude of your aircraft and the conflicting aircraft altitude. You could be inverted, it only reads transponder altitude and climb or descent rate of the other aircraft. Just turn out of the way.
Remember how we did it 30 years ago, see and avoid? |
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