TCAS RA

[qualityjet]

Hi!

What do you think, can TCAS give you a climb command when you are flying your max FL? So does it know anything about ac's performance?

Just thinking...

[deptrai]

Follow the RA, trade speed/inertia for height (and avoid stalling), you're trying to avoid a collision, not to cruise. Generally TCAS are not aware of aircraft performance, though many inhibit climb RA above a certain altitude (check with your outfit). Where that is the case, when 2 level a/c are on collision course, TCAS will generate a descend RA for one and keep the other level.

[Wizofoz]

TCAS takes performance into consideration- it will give you a climb at max altitude, but one your residual performance can handle.

[tubby linton]

At altitude the pitch change to achieve the required miss is quite small if you have a TAS of 7-8 miles per minute.

[deptrai]

TCAS takes performance into consideration- it will give you a climb at max altitude, but one your residual performance can handle.

Afaik TCAS is NOT aware of actual performance limits, e.g. degraded performance due to loss of an engine, but some limits have been taken into consideration during certification.

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_120-55C_CHG_1.pdf :

(1) Aircraft not inhibited to climb when at maximum certified altitude should climb in response to TCAS climb RAs.
(2) Aircraft that are climb-inhibited from TCAS climbs at maximum certified altitude will be issued a “DO NOT DESCEND” RA.

and (courtesy of airbus)

AC 20-131A defines the maneuvers that the aircraft must be able to perform.
• In particular, the aircraft must prove that it can respond to a TCAS RA CLIMB order, even when it is at its maximum altitude.

( AC 20-131A here: https://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/22190 )

[Wizofoz]

Correct depral- so you CAN comply with an RA even if it is "CLIMB" while at max altitude.

Also right about single engine- which is why S/E checklists (on Boeing anyway) include putting TCAS into TA only.

[Thai Pom]

During the installation there is Pin Programming that is done that sets the aircraft ceiling. TCAS should not issue a climb RA if this height will be reached.


Cheers, TP

[latetonite]

..and the pin is changed with Every weight?

[Wizofoz]

Thai Pom,

Not the impression I was under- do you have a reference?

[Thai Pom]

No it is part of the certified engineering package, based on the certified Ceiling from the OIM. I believe in later installs it can be changed visa the MCDU but I am not sure on that.


TP

[deptrai]

Generally aircraft have been tested that they can comply with RAs in most scenarios. During installation, various inhibit parameters can be set, most obviously AGL, but also configuration; this will depend on manufacturer/type, and your outfit.

[JAR]

Embraer 170-195:

TCAS​ WARNING​ INHIBITIONS

No​ CLIMB​ commands​ or​ INCREASE​ CLIMB​ commands​ are​ issued​ at​ or above​ 34000​ ft​ MSL.​

[Pin Head]

Read a circular once from the European safety agency before EAsA and ITBASICALLY implied instigate some sort of a climb (even the slightest) at max altitude as it will relay and coordinate with the other a/c and force him into a descent.

Pin

[GlobalNav]

"( AC 20-131A here: https://www.faa.gov/regulations_poli...cumentID/22190 )"

There is a more current AC now - AC 20-151B and here's a brief excerpt:
2-16. Aircraft Performance Considerations. Use paragraphs 2-16 through 2-17 and Table 1 of this AC to help you evaluate the need to inhibit TCAS II CLIMB and/or INCREASE CLIMB RAs resulting from inadequate aircraft climb performance. The collision avoidance maneuvers posted as RAs by TCAS II assume an aircraft’s ability to safely achieve them. If it’s likely the required response to CLIMB and INCREASE CLIMB RAs are beyond the performance capability of the aircraft, then TCAS II must know beforehand so it can change strategy and issue an alternative RA.

[ACMS]

Really?
So what if both Aircraft are operating at their max altitudes?

Bang?

Doubt it.

[West Coast]

Page not found

[Thai Pom]

One of them would be given the "descend" command ?

[ACMS]

Thai----obviously one would, posters here said that a RA to climb would not be given above Max Alt.

I'm simply pointing out that idea is wrong.

[ACMS]

From the A330 FCTM, it says you MUST follow the RA even if above Max Alt

If a RA is generated:
• The flight crew must always follow the TCAS RA orders in the correct direction, even:
‐ If the TCAS RA orders are in contradiction with the ATC instructions
‐ At the maximum ceiling altitude with CLIMB, CLIMB or INCREASE CLIMB, INCREASE CLIMB TCAS RA orders
‐ If it results in crossing the altitude of the intruder.

[deptrai]

that a RA to climb would not be given above Max Alt. I'm simply pointing out that idea is wrong.

again, it depends on type.

[ACMS]

I very much doubt any Jet wouldn't have energy to fly a little above Max Alt trading a little speed for height in an RA situation.

Look at AF447 and how far above Max Alt they went before they totally deep stalled......quite a way. ( not that I'm suggesting that crazy a pull back ever!! )

[deptrai]

agreed. Most modern jets do not have a problem at all to climb above their max altitude. However, there are exceptions. The altitude at which 1500/2500 fpm climb can no longer be achieved is determined by the manufacturer, and if necessary, programmed into the TCAS processor. That altitude is pretty low in a 747-100 in partial flaps configuration, hence 747-100 TCAS climb RAs are inhibited based on altitude and flaps. Jet mentioned Embraer 170-195. In some types, climb RAs are inhibited based on performance parameters. A330 is not one of them.

(and some thread drift: speaking of crazy pull backs...I remember reading somewhere that most pilots overreact to RAs. Edit: cue automation debate. Airbus has determined that switching off AP and FD and adjust pitch to get the proper V/S is "quite unfamiliar" and disruptive, which adds to the stress level of an RA. Apparently A380 and A350 have an AP/FD TCAS mode, and Airbus offers this as an upgrade for other types)