Which FAA regulations require compliance with TCAS II Resolution Advisories?

Question

I've always heard that complying with a TCAS II Resolution Advisory is a required action for pilots qualified and operating an equipped aircraft. I am not familiar with the regulatory basis for this, though. I'd like to get a bit more specific with the context. For aircraft operating under 14 CFR 91, is there a regulation that can be referenced?? For aircraft operating under 14 CFR 135, is there a regulation that can be referenced? And what about for 14 CFR 121?

I'd also like to know if there are exceptions to any regulatory requirements.

This answer mentions that aircraft must respond within 6 seconds. I believe the source is AC 120-55C but I'm not totally sure.

Answer 1

The requirement to respond to the TCAS II resolution advisory is somewhat indirect. one key fact is that any TCAS installation has to be approved:

14 CFR §91.221 Traffic alert and collision avoidance system equipment and use.

(a) All airspace: U.S.-registered civil aircraft. Any traffic alert and collision avoidance system installed in a U.S.-registered civil aircraft must be approved by the Administrator.

(b) Traffic alert and collision avoidance system, operation required. Each person operating an aircraft equipped with an operable traffic alert and collision avoidance system shall have that system on and operating.

Key points here: 1. The installation must be approved. 2. If it's installed, it has to be used.

From Part 121:

14 CFR §121.356 Collision avoidance system.
Effective January 1, 2005, any airplane you operate under this part must be equipped and operated according to the following table: {Detail omitted}

This says anyone under Part 121 must have A TCAS installed and operating.
If you go back to Part 21, you can find that the installation approval requires a Type Certificate, Supplemental Type Certificate, or an Amended Type Certificate.

Part of getting that installation approval is a requirement for Airplane Flight Manual (AFM) or an AFM Supplement. With regards to TCAS, the airworthiness approval is addressed by

AC 20-151B Airworthiness Approval of Traffic Alert and Collision Avoidance Systems (TCAS II), Versions 7.0 & 7.1 and Associated Mode S Transponders

Chapter 5 and Appendix A cover the requirements for the AFMS for TCAS.

While the AC is advisory, it is spelling out a means of complying with the rules, which in Part 23 (small A/C) and Part 25 (air transport) require a flight manual.

Elsewhere:

14 CFR §91.9 Civil aircraft flight manual, marking, and placard requirements.

requires operation in accordance with the limitations of the AFM.

In Part 121, airlines operate in accordance with their Op Spec, which will include similar rules.

And there is specific wording to address clearances and response to TCAS:

14 CFR §91.123 Compliance with ATC clearances and instructions.
(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.
(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.
(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.

This basically acknowledges that pilots will respond to an RA and that they should report it as soon as they can after the fact.

Answer 2

14 CFR 91 Appendix G Section 2 (g)

Traffic Alert and Collision Avoidance System (TCAS) Compatibility With RVSM Operations: All aircraft. After March 31, 2002, unless otherwise authorized by the Administrator, if you operate an aircraft that is equipped with TCAS II in RVSM airspace, it must be a TCAS II that meets TSO C-119b (Version 7.0), or a later version.

14 CFR 121.356

Effective January 1, 2005, any airplane you operate under this part must be equipped and operated according to the following table...

14 CFR 135.180

Unless otherwise authorized by the Administrator, after December 31, 1995, no person may operate a turbine powered airplane that has a passenger seat configuration, excluding any pilot seat, of 10 to 30 seats unless it is equipped with an approved traffic alert and collision avoidance system. If a TCAS II system is installed, it must be capable of coordinating with TCAS units that meet TSO C-119.

TSO C-119

Also see AC-120-55 for information about operational use and required training for parts 91, 121, and 135. Specifically Section 12 "TCAS Operational Use" outlines how the crew is required to respond to TA's and RA's. It is a few pages long so not appropriate to duplicate here.