Comply with TCAS or with ATC?
Several contributers to this thread have asked the question, "Should a pilot comply with ACAS (ie TCAS II) Resolution Advisories (RA) or with instructions from ATC?"
The answer can be found in the guidance material published by ICAO - for international application - where two critical paragraphs state:
"When simultaneous, conflicting instructions to manoeuvre are received from ATC and an RA, the RA (should be) followed", and,
"If a justified decision is made not to follow an RA, the resulting existing vertical rate (must not be made) in a direction opposite to the sense of the displayed RA."
Earlier text, published circa 1997, contained similar advice but used slightly different words.
Of course, ICAO expects contracting States to reflect these guidelines in its regulations so that pilots and controllers know what to expect.
Increased emphasis is now being brought to bear by ICAO on States to require commercial air transport operators to address, "Policy, instructions, procedures and training requirements for the avoidance of collisions and the use of the airborne collision avoidance system" and on the expectation that pilots who receive an RA will comply with it unless doing so would jeopardise the safety of the aeroplane.
Because ICAO Standards and Recommended Practices concerning ACAS (TCAS II) apply only to the larger commercial air transport (CAT) aeroplanes, there is no direct connection between operations manual contents and guidelines on the one hand, and other aircraft that have ACAS/TCAS II, such as corporate/business aeroplanes, the smaller CAT aeroplanes, and some helicopters on the other. Nevertheless, until ICAO addresses this anomaly directly (and they are aware of it), we must hope that pilots who fly these other types will also follow the ICAO guidelines so that everyone applies the same procedures.