After start checklist asks for transponder/TCAS to TA/RA instead of ALT ON

[DanielR]

Hi,

the "after start" checklist asks for the transponder/TCAS mode set to TA/RA. As per the procedures I'm used to, shouldn't this be ALT ON instead?

TCAS is being enabled (TA/RA) only when entering the runway, not already on taxi-out?! The "before takeoff" checklist has ATC TA/RA, so this would be redundant if already done in the "after start" flow - another indication that the "after start" one is probably wrong.

Best regards,
Daniel

[Pils]

43 minutes ago, DanielR said:

Hi,

the "after start" checklist asks for the transponder/TCAS mode set to TA/RA. As per the procedures I'm used to, shouldn't this be ALT ON instead?

TCAS is being enabled (TA/RA) only when entering the runway, not already on taxi-out?! The "before takeoff" checklist has ATC TA/RA, so this would be redundant if already done in the "after start" flow - another indication that the "after start" one is probably wrong.

Best regards,
Daniel

It was changed to be more universally applicable, feel free to edit the checklist.xml and do your own SOP.

[DanielR]

I don't understand that argument. In what scenario does it make sense to go through the taxi checklist, enabling TCAS prematurely, and not going through before takeoff checklist?

To quote https://skybrary.aero/articles/tcas-ii-activation:

Quote

However, present-generation TCAS equipment may cause interference to radar surveillance systems, which operate in the same frequency band (1030-1090 MHz), and to other (airborne) TCAS systems. Because of this, it is very important that aircraft only select their TCAS to TA/RA when approaching the holding position for their departure runway or, if so desired, when approaching to cross an active runway during taxiing. In the latter case, the setting must revert to ‘Transponder Only’ once clear of the active runway. It is equally important that TA/RA is deselected as soon as possible after clearing the landing runway. This circumstance is addressed in ICAO PANS-OPS Doc 8168 (and also the ACAS Manual Doc 9863) where it is recommended that TCAS II not be operated (at all) whilst taxiing.

This is pretty clear. Enablement of TCAS in the before-taxi checklist is, sorry, plain wrong and against strong real-world recommendations.

STDBY on parking, ALT ON for taxi, TA/RA when entering any runway, back to ALT ON after leaving runway, STDBY on parking.

I'm really interested what scenario made you deviate from that.

[Peter Clark]

U.S. AIM 4-1-20 paragraph 3 says the same thing, “on“ before surface movement.

[Graeme_77]

This is something that was discussed during development and testing. The real world operator that has been assisting Hot Start has TCAS selected TA/RA before taxi, and this reflects my airline experience of operating in TA/RA mode during taxi without limitation. TCAS 7.1 hardware does not have any issues with this behaviour.  As Pilsner mentioned, you can customise it yourself at will, but the SOPs supplied are in use on real aircraft operating globally.

Please remember there is a whole wide world beyond FAA procedures ;-)

As to why it exists in two places on the checklist, the original procedure allowed for ALT ON only, or if there is a specific airfield prohibition so the second item verifies. Airbus checklists do the same with Flaps on both after start and before takeoff, to accommodate taxi in contaminated conditions.

 

Edited January 31, 2022 by Graeme_77