TCAS Equipment Use

FAR 91.221 — TCAS Equipment Use

FAR 91.221 requires TCAS in U.S.-registered civil aircraft to be FAA-approved and turned on during operation. Study guide for pilot students.

In Plain English

FAR 91.221 covers the Traffic Alert and Collision Avoidance System (TCAS) — the onboard equipment that warns pilots of nearby traffic and, in advanced versions, issues climb/descend commands to avoid collisions.

The rule has two simple but important requirements:

Approval: Any TCAS installed in a U.S.-registered civil aircraft must be approved by the Administrator (the FAA). You can't bolt in a non-certified collision avoidance unit and call it TCAS.
Operational use: If your aircraft is equipped with an operable TCAS, you must have it turned on and operating whenever you fly.

Why it matters: TCAS is a critical last layer of defense against midair collisions, especially in busy airspace. Turning it off — even to reduce alerts or workload — defeats the safety benefit and violates Part 91. If the unit is installed and works, it stays on. The rule does not, by itself, require you to install TCAS; it governs how installed systems must be approved and used.

Regulation Text

14 CFR § 91.221

§ 91.221 Traffic alert and collision avoidance system equipment and use. (a)Any traffic alert and collision avoidance system installed in a U.S.-registered civil aircraft must be approved by the Administrator. (b)Each person operating an aircraft equipped with an operable traffic alert and collision avoidance system shall have that system on and operating.

Oral Exam Questions a DPE Might Ask

Q1If your aircraft has TCAS installed and working, are you required to use it?

Yes. Per FAR 91.221, any operable TCAS installed in the aircraft must be turned on and operating during flight.

Q2Can you install any collision avoidance unit you like in a U.S.-registered civil aircraft?

No. FAR 91.221 requires that any TCAS installed in a U.S.-registered civil aircraft be approved by the Administrator (the FAA).

Q3What should you do if the TCAS is inoperative before flight?

FAR 91.221 only requires an *operable* TCAS to be on and operating, so an inoperative unit doesn't violate this section — but you must still address it under the inoperative equipment rules (e.g., FAR 91.213) and any applicable MEL.

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Related Sections in Part 91

§ 91.1

Part 91 Applicability