Hi, I am just wondering what would happen if you are cruising at or just below the certified maximum altitude and a tcas ra goes off? You obviously can't climb higher so what do you do?
Compared to doing nothing climbing is the better option is it not? Its not the absolute ceiling so there will be some room left to manoeuvre within and maybe 10 - 20 knots of speed to trade in short term, possibly a good reason not to climb to the maximum possible altitude straight away? If its that tight a margin on performance then perhaps the operator should mandate you put the transponder to TA only? Just a few thoughts, but I reckon following it as best you can would be the best bet.
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Most often max certified crz level is not an absolute level as someone above stated. It's often a certified altitude of a 2 % buffet margin or sometimes higher depending on the aircraft. Also governing the max crz alt is the maximum cabin pressure differential. But there is always a safety margin built into that so the aircraft most often can climb all the way up to an absolute altitude...
so always follow TCAS what ever it might say.
As a note, you should be aware of the new communication prescribed in case of a TCAS RA issued by ICAO in May 2008.
A review of this thread may be useful. TCAS is inhibited where the aircraft performance is inadequate to respond to the RA, this would apply for this case too.
Yes it does, when the system became mandatory at about the turn of the century, I was busy installing it into a lot of aeroplanes. I distinctly remember installing a particular fit into a B737-200 which would then be used to gain the STC for installation into other 737-200s so there was a lot of FAA testing and inspection involved. From memory I know there was an input from the flap switches (F40 to be precise) to ensure that with the flaps at 40 a climb RA would never be issued regardless of the scenario, there was also an input from the air data computers to ensure that at max certified altitude there would not be a climb RA generated. In testing we had to recreate these scenarios with test equipment and it all worked as advertised....
Just to elabourate on the answer I gave in that previous thread. I remember during the testing of that part of it the max certified altitude to which TCAS was not allowed to issue a 'Climb RA' was actually much higher than the max altitude the A/C would usually operate at, I can't remember the exact figure but it was either 40000ft or 50000ft.
Only because some things stick in the mind, whilst others don't, would I have posted that TCAS will not issue RA's outside of the aircraft's current performance capabilities to achieve the RA regardless of specified aircraft limitations so spot on.
Then begs the question - if TCAS recognises danger but also recognises a lack of performance ability what happens ?? Does it re-work any possible options to avoid the conflict - or does it default to (literally) throwing it's arms in the air and saying "too hard, not my problem!!"
If both aircraft involved in a conflict have TCAS, then between the two TCAS systems they will agree a solution. For example, if you are at Max Altitude, and someone is climbing to your level, although you may not be able to go up, they will still be told to reduce or stop their climb.
If TCAS cannot give you a resolution because of inhibit logic, it will give you a Traffic alert instead and let you figure something out. Actual inhibit inputs are airframe dependent, but can include air data inputs (altitude), gear position, flap position, and so on.
Slight change of thread - is it just my imagination, or have there been quite a lot of fairly basic TCAS questions on PPRuNe? I don't want to be rude, but isn't "everything you ever needed to know about TCAS" taught in pilot school any more?
Although there are lots of clever algorithms inside the box, the end result is actually pretty simple, and (at least I always thought) completely understandable in about 5 minutes.
Hi folk, If the question is from a 320 "Busdriver", the answer is that you will follow the RA. The 320 alt limit is more a result of Engine thrust avail than the aerodynamics of the aircraft. The aircraft is able to momentarily climb above without a problem. Follow the RA in all cases - except one. That is if you get an additional GPWS warning of "Terrain Pull Up". Then the GPWS warning takes priority. You may miss the traffic but if you don't follow the GPWS you won't miss the ground.
Max Certified aircraft altitude is setup with hardwired jumpers into the back of the Tcas computer. When I have tested aircraft on ground with the test box using a scenario of two aircraft at or near Max altitude and a conflict the RA is co-ordinated with sufficient time to prevent aircraft having to climb.
Hi...this is from a paragraph in a book titeled AIRCRAFT DIGITAL AND ELECTRONIC COMPUTER SYSTEMS quote: It is important to be aware that TCAS provides only vertical guidance...TCAS also ignores performance limitations, in other words, when flying at maximum altitudes, TCAS may still generate a climb command unquote:
now the term max altitudes was not elaborated upon so i don't know what to make of it bf
I believe that you have 1.3g to the buffet margin at max cert alt. That gives you plenty of room to manouvre at the height if you really need it. I would suggest in the case of an RA you need it. It is perfectly safe and reasonable, however your AFM is the authority.
Miles Magister, a reminder to avoid any misunderstanding, the 1.3 buffet margin is a turning flight requirement. TCAS manoeuvres are only vertical and are approximately defined by pull up (1.25 g), reaction time, and the required altitude/rate change; these factors (and configuration if applicable) define the TCAS limit at maximum altitude.
bflyer, the figures that I quoted were approximate, I do not know for sure that theyapply to all altitudes.
The Eurocontrol hosted document Operational use and Pilot training guidelines indicates that the maneuver requirements assume increments between 1/4g to 1/3g (1.25 – 1.33g) depending on the alert, and that the required VS is achieved in 2.5 sec; the information suggests that these apply at all altitudes. The technical information in this document should be crosschecked with the latest ACAS technical spec as some performance aspects may have changed with recent updates.
Not quite right PEI_3721. The required VS will be reached in however long it takes using the specified acceleration. The times quoted in the guidelines are the delay from the issue of the RA to the pilot moving the stick. For an initial RA the required acceleration is 1/4g with the manouevre starting no longer than 5 seconds after the RA is issued. For a subsequent change in RA the required acceleration is 1/4g (for weakening RAs or "normal" strengthening RAs) or 1/3g (for RA reversals and RAs strengthening to "INCREASE CLIMB"/"INCREASE DESCENT") in both cases starting no longer than 2.5 seconds after the change in RA is issued. These accelerations and times are indeed applicable at all altitudes.
This is all assumes of course that the robots flying the plane do exactly with the RA tells them to do. This is where judgement takes precident over a box.Your right in the coffin corner, do you climb because the RA tells you to? Your on approach at the MDA, IMC, do you decend because the RA tells you too? Your VMC right below the clouds on a visual approach...do you climb into the soup because the RA tells you to? I bought a TCAS I unit and chose not to go TCAS II for the extra $100k...I figured, the pilot should know when to climb or descend.
Thanks for the clarification fellman. Are you quoting from the same training reference that I used? The Eurocontrol training materials link has another reference stating ‘5 sec’, but without specific application, i.e. 5 sec from alert to achieved VS, or 5 sec during the maneuver – its unclear.
My recollection during testing a system many years ago was of 2.5 sec ‘surprise’ (reaction) time plus 2.5 sec maneuvering. The use of ‘g’ in a specification is fine providing the aircraft has an accelerometer, but in practical terms, a pilot requires specific guidance as to what a ‘smart’ maneuver is. Some of the training materials provide values of pitch change for speed, but the rate of pitch and feel of the maneuver will be aircraft specific, so practice is required.
Lookforshooter, the main point which has been made in many threads on ACAS is that pilots must follow the RA. This is a matter of discipline – airmanship. As already stated, when an aircraft is at it’s maximum altitude, no Climb instruction will be given so the pilot does not have to consider performance, nor weather. There are similar safeguards at low altitude so that ACAS will not demand hazardous flight towards the ground.
A danger in aviation is from those pilots who figure that they know better than the system. If you do not follow a RA then you may cause an accident – it will be your accident as you will be part of the collision; no thinking, no judgment, just follow the RA.
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except one. That is if you get an additional GPWS warning of "Terrain Pull Up". Then the GPWS warning takes priority. You may miss the traffic but if you don't follow the GPWS you won't miss the ground.
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