"By the way what section of the advisory has the TA only ? It’s not in 9.1"
This is copy/paste from Eurocontrol ACAS II bulletin #9 July 2007.
Degraded performance:
TCAS II provides maximum benefits when operated in RA mode and when all RAs are followed promptly and accurately. However, when the aircraft performance is degraded (e.g. an engine failure, an emergency descent, etc.), it might not be possible to comply with a “Climb” RA.
Therefore, airlines must define clear procedures to address degraded aircraft performance situations, having in mind that:
• When operated in RA mode, non-compliance with an RA will adversely affect the efficiency of the coordinated RA triggered on- board the other aircraft.
• When operated in TA-only mode, collision avoidance is still maintained by the TCAS II of the other aircraft
The use of the TA-only mode is described in the following note that will be included in the next version of the ICAO PANS-OPS, Doc 8168, due in November 2007:
“Note 2. - The normal operating mode of ACAS is TA/RA. The TA-only mode of operation is used in certain aircraft performance limiting conditions caused by in-flight failures or as otherwise promulgated by the appropriate authority.”
Note the comment: "airlines must define clear procedures.........." When I brought this to my Flt Ops attention there was a blank stare, especially as there had just been an extensive RST program emphasising emergency descent procedures. It took a good long while but it crept into the QRH eventually. However, it was the most missed item in any exercise. When I suggested the whole matter of TA Only should be discussed, especially on command courses, the blank stare reappeared. Is it going to take a mid-air to open eyes.