Proper response to TCAS Alerts

[torrence]

I've been mostly flying with Traffic in "Low conflict random loop" mode.  This still produces occasional TCAS alerts - I hope at lower probabilities that real life, but I found I was having trouble complying without getting into over- or low- speed conditions.  I realized that my basic problem was I was trying to climb, descend, increase rate etc. using the MCP autoflight settings - duh, where have I heard that before.  I got much better results when I just disconnected Auto Throttle and Auto Pilot and used the throttle as primary to control climb/descend TCAS commands. I haven't seen this discussed in the various tutorials, so my question is basically 'what are the standard procedures for TCAS responses?" 

Summary of my question is "Is response to TCAS alerts basically just "Click-click Click-click", then maintain course and control altitude and rates with throttle while staying out of red-bricks?"  I don't mind if this is a stupid question - this forum has a very enlightened (there are no stupid questions) view on this.

Cheers,
Torrence

[Hardy Heinlin]

Hi Torrence,

I'll leave the questions to the others; I just want to add that conflicts will be even rarer when the "Start a semi-random preset" checkbox is selected (the 5th checkbox).


Cheers,

|-|ardy

[double-alpha]

Hi Torrence

I don't fly the 747, but according to an old QRH:

If maneuvering is required, disengage autopilot and disconnect autothrottle.
Smoothly adjust pitch and thrust to  satisfy the RA command.
Follow the planned lateral flight path unless visual contact with the conflicting traffic requires other action.

[double-alpha]

If you fly an airbus a340 :

Traffic advisory: "TRAFFIC" messages:
PF - Do not perform a maneuver based on a TA alone.

Resolution advisory: All ″CLIMB″ and ″DESCEND″ or ″MAINTAIN
VERTICAL SPEED MAINTAIN″ or ″LEVEL OFF, LEVEL OFF″ or ″MONITOR VERTICAL SPEED″ type messages:
PF - AP (if engaged).......................OFF
PF - BOTH FDs.................................OFF
Respond promptly and smoothly to a RA by adjusting or maintaining the pitch, as required, to reach the green area and/or avoid the red area of the vertical speed scale.
Note: Avoid excessive maneuvers while aiming to keep the vertical speed just outside the red area of the VSI, and within the green area. If necessary, use the full speed range between Vαmax and VMAX.
PF - Respect stall, GPWS, or windshear warning.
PM - Notify ATC.

The GO AROUND procedure must be performed, when a RA "CLIMB" or "INCREASE CLIMB" is triggered on final approach:
Note: Resolution Advisories (RA) are inhibited below 900 ft.

When "CLEAR OF CONFLICT" is announced:
Resume normal navigation in accordance with ATC clearance.
AP/FD can be reengaged as desired.

[Hardy Heinlin]

Follow the planned lateral flight path unless visual contact with the conflicting traffic requires other action.
[...]
If you fly an airbus a340 :
[...]
PF - BOTH FDs.................................OFF

How will you follow the planned path when the FDs are off? By including the ND in the instrument scan?

Why should the FDs be off anyway? To see the RA command better?


Regards,

|-|ardy

[double-alpha]

AFAIK Airbus doesn't give instruction to follow the planned lateral flight path... I guess you should follow the ND ... Anyway, during OPC checks, TCAS RA doesn't last very long, I keep wings level during the procedure.

You don't need FDs because you only have to follow the green area of the vertical speed scale.

But you MUST set FDs OFF once Autopilot is disconnected :
- to ensure the A/THR (autothrust) automatically reverts (or remains in) SPEED/MACH mode (*),
- and to avoid possible confusion between FD bar orders and TCAS aural and VSI orders

(*) for example, you are in climb, A/THR is in THR CLB mode, and you have a "DESCENT / DESCENT" TCAS RA.
The crew forget to switch OFF both FDs.
A/THR remains in THR CLB mode during the descent in manual... when speed reaches speed limit : high speed proctection activates (the pitch nose-down authority smoothly reduces to zero!)

Cheers

[torrence]

Thanks for the rapid response.  Sounds like the main difference between 747 and airbus in this case is making sure the throttle control is put in appropriate mode - for the 747 simply disconnecting autothrottle with the  buttons on the throttle, for Airbus the FD off ensuring the proper SPEED/MACH mode? 

Hardy - thanks for the reminder on the various Traffic modes.  I remember now I had most of my situ's set in low conflict mode to get some TCAS response practice without being swamped with dodging intruders all the time.   

Cheers,
Torrence

[IefCooreman]

In case of TCAS RA (not the TA's), Boeing requires you to disconnect AP and AT and fly the maneuver manually. FD commands are not to be followed, although you will encounter pilots who (ask to) flick off the FD on their side if it bothers them.

The PFD shows you "attitude zones to steer away from". The maneuver calls for "smooth pitch adjustment" avoiding aggresiveness at all cost to avoid unwanted high/low wing loading (wich happens quickly if ie you are in a high speed descent). TCAS RA's are supposed to give you time to do the maneuver. The TCAS RA's that end up in red zones on the upper and lower side of the attitude range can be tricky, which is one more reason it is more prefered to be gentle but precise than too aggresive with less preciseness (if that's a word...?)

[simonijs]

A little late with this reply, but nevertheless...:

Eurocontrol so far has published 22 "ACAS Bulletins", each one containing four to five events in which pilots were not responding properly to an RA, or were maneuvering based on a TA instead of following ATC instructions. Each described event is followed by Learning Points (usually for pilots) and extracts from ICAO (PANS-OPS DOC 8168; ACAS Manual DOC 9863).

Although the bulletins primarily are meant for pilots, not very many of them are aware of the existence of such informative material.

The link to the list of the ACAS bulletins: http://www.eurocontrol.int/publications?title=&field_term_publication_type_tid=233&year[value][year]=

Kind regards,
Simon

[double-alpha]

Torrence, are you OK now with your Tcas?

Regards

[torrence]

Yes indeed.  Thanks for the helpful background.  I had figured that disconnecting the autos and making primarily throttle adjustments was the best RA response (vs fiddling around with VNAV, FLCH, V/S etc.).  Glad to have the addition info of smooth adjustments, ignoring (or turning off) the FD, and staying out of the red zones.  Also, I had probably being too aggressive in response when that "Descend, descend NOW" message comes on (Adrenalin shot).  Nice to know the alert logic is supposed to allow time for the response.

Cheers,
Torrence