FAR 91.225 Explained: ADS-B Out Requirements Made Simple for Student Pilots

FAR 91.225 Explained: ADS-B Out Requirements Made Simple for Student Pilots

By Rhonda Simons-Chang, CFI/CFII

Automatic Dependent Surveillance–Broadcast (ADS-B) is one of the most important technology changes modern pilots must understand. FAR 91.225 lays out when and where ADS-B Out is required, and it’s a topic that comes up frequently during training, written exams, and checkrides. This guide breaks ADS-B down into plain language, explains the difference between ADS-B Out and ADS-B In, and shows how ADS-B improves safety and situational awareness for pilots.

What Is ADS-B?

ADS-B stands for Automatic Dependent Surveillance–Broadcast. That sounds complicated, but the idea is simple:

  • Automatic: The system works on its own—no pilot action required

  • Dependent: It depends on GPS position data

  • Surveillance: It’s used to track aircraft

  • Broadcast: Your aircraft broadcasts its position and information to others

With ADS-B, your airplane continuously broadcasts:

  • GPS position

  • Altitude

  • Ground speed

  • Aircraft identification (call sign or tail number)

This information is received by ATC and by other ADS-B–equipped aircraft.

ADS-B Out vs ADS-B In (What’s the Difference?)

This is one of the most common points of confusion for student pilots.

ADS-B Out

ADS-B Out is the required part.

  • Sends your aircraft’s position and information out to ATC and other aircraft

  • Replaces radar in many areas

  • Required by FAR 91.225 in certain airspace

Think of ADS-B Out as your airplane saying, “Here I am.”

ADS-B In

ADS-B In is optional.

  • Receives information from other aircraft and ground stations

  • Allows pilots to see traffic (TIS-B) and weather (FIS-B) on cockpit displays or tablets

  • Not required by regulation

Think of ADS-B In as your airplane saying, “Here’s what’s around me.”

Many aircraft have ADS-B Out only, while others have both Out and In.

How ADS-B Helps Pilots

ADS-B improves both safety and efficiency.

Better Traffic Awareness

With ADS-B In, pilots can:

  • See nearby traffic even without radar coverage

  • Spot aircraft that may not be visible visually

  • Improve situational awareness in busy airspace

Improved ATC Services

For ATC, ADS-B provides:

  • More accurate aircraft position data than radar

  • Coverage in areas where radar doesn’t exist (mountains, remote areas)

  • Faster and more precise traffic separation

Enhanced Safety

ADS-B reduces the risk of midair collisions by:

  • Making aircraft more visible electronically

  • Improving traffic alerts

  • Allowing ATC to track aircraft with greater accuracy

FAR 91.225: When Is ADS-B Out Required?

FAR 91.225 specifies where and when ADS-B Out is required. If ADS-B Out is required, it must be operational.

ADS-B Out Is Required In:

  • Class A airspace (FL180 and above)

  • Class B airspace

  • Class C airspace

  • Within 30 NM of a Class B primary airport (the Mode C veil)

  • Above the ceiling and within the lateral boundaries of Class B or C airspace, up to 10,000 feet MSL

  • Above 10,000 feet MSL (excluding airspace at or below 2,500 feet AGL)

If you’ve learned Mode C transponder rules, this list should look very familiar. ADS-B Out largely mirrors those requirements.

When Did ADS-B Out Become Mandatory?

ADS-B Out became mandatory on January 1, 2020.

Any aircraft operating in the airspace listed under FAR 91.225 must be equipped with compliant ADS-B Out equipment.

What Happens If You Don’t Have ADS-B Out?

If your aircraft is not ADS-B Out equipped:

  • You cannot legally operate in airspace where ADS-B Out is required

  • ATC authorization is extremely limited and rarely granted

  • Most training and cross-country operations require ADS-B–equipped aircraft

This is why nearly all training aircraft today have ADS-B Out installed.

Common Student Pilot Questions About ADS-B

Do I need ADS-B In?

No. ADS-B In is not required, but it’s highly beneficial for traffic and weather awareness.

Is ADS-B the same as a transponder?

Not exactly. ADS-B Out works with a transponder or as part of an integrated system. Many aircraft use a Mode S transponder with ADS-B Out.

Does ADS-B replace see-and-avoid?

No. ADS-B is a supplement, not a replacement. Pilots must still maintain visual scanning at all times.

Final Takeaway

FAR 91.225 and ADS-B Out are core knowledge areas for student pilots. In simple terms:

  • ADS-B Out: Required. Broadcasts your aircraft’s position

  • ADS-B In: Optional. Lets you see traffic and weather

  • Required airspace: Class A, B, C, Mode C veil, and above 10,000 feet MSL

Understanding ADS-B early in your training will help you fly legally, safely, and confidently—both on your checkride and in the real world.

By Rhonda Simons-Chang, CFI/CFII

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