TIS-B, the Radar Ghost Fleet Hidden Inside Your ADS-B Display, and the Latency Numbers Every Pilot Needs Before Trusting That Traffic Warning

The traffic target on your ADS-B display may not be what you think it is. A significant portion of what you see comes not from aircraft broadcasting their own position, but from radar data the FAA is rebroadcasting through its ground network - a system called TIS-B. Understanding the difference directly affects how much confidence to place in any given traffic alert.

What Is TIS-B?

TIS-B stands for Traffic Information Service-Broadcast. It is a radar-to-cockpit relay system built directly into the ADS-B ground infrastructure. When a radar facility - typically an Air Route Traffic Control Center - detects an aircraft with no ADS-B Out capability, it converts that radar return into a digital traffic target and pushes it out over the same ADS-B frequencies your receiver is already monitoring.

The result is that non-equipped aircraft - those with only a Mode C or Mode S transponder and no ADS-B Out - appear on your traffic display alongside fully equipped aircraft. TIS-B makes those aircraft visible. It does not make them equivalent to ADS-B Out targets.

How the ADS-B Mandate Created Two Kinds of Traffic

The ADS-B Out mandate, which took effect in January 2020, requires aircraft operating in Class B or Class C airspace, or above 10,000 feet in the contiguous 48 states, to continuously broadcast position, altitude, velocity, and identification. That broadcast goes out on one of two frequencies: 978 MHz for UAT-based installations (common in general aviation piston aircraft) or 1090 MHz for Mode S transponder-based systems (airlines and most turbine aircraft).

Those broadcasts reach two audiences: FAA ground stations, which relay the data to ATC; and any aircraft equipped with ADS-B In, the voluntary receiver that displays traffic and free weather in the cockpit. ADS-B In is where TIS-B enters the picture. The ground stations that relay your position to ATC also push radar-derived traffic back down to your cockpit.

How Much Latency Does TIS-B Introduce?

An ADS-B Out-equipped aircraft broadcasts its own GPS-derived position at once per second, with position accuracy typically within a few meters. The total time from actual position to your display is roughly 2 to 4 seconds, accounting for broadcast cycles and receiver processing.

A TIS-B target follows a longer chain. The radar site picks up the return. That data moves to the Air Route Traffic Control Center. The center passes it to the TIS-B broadcast subsystem. An FAA ground station rebroadcasts it. Your receiver picks it up and your display renders it.

According to FAA documentation, TIS-B latency can range from 6 to 12 seconds - and in some cases, depending on radar site location and data forwarding paths, longer. An aircraft traveling at 150 knots covers roughly 2.5 miles per minute. In 12 seconds, that is approximately half a mile of potential position error in any direction.

That is not a reason to distrust the system. TIS-B provides genuine situational awareness value. It is a reason to interpret TIS-B targets with appropriate calibration.

How to Identify TIS-B Targets on Your Display

Most ADS-B In receivers differentiate between target types through symbol shape or color. On Garmin displays, a yellow diamond typically indicates a direct ADS-B Out target - a self-reported position. A white diamond or simplified target shape typically indicates a TIS-B-derived target. The exact symbology varies by manufacturer and software version.

This distinction is worth fifteen minutes with your receiver’s documentation. The symbols are not always intuitive, and knowing which shape carries which level of position confidence directly affects how you weight a traffic alert.

Where Does TIS-B Coverage Break Down?

The FAA’s Aeronautical Information Manual identifies two requirements for TIS-B service: an ADS-B ground station must be within range, and a radar facility must be covering that same airspace. Both pieces of the infrastructure must be present and functioning.

The United States has more than 700 ADS-B ground stations. Coverage above 10,000 feet across the contiguous 48 states is essentially complete. Below 10,000 feet, coverage is strong in most areas but has gaps - particularly in mountainous terrain and remote regions. Below 3,000 feet AGL, those gaps grow significantly.

For pilots flying low-altitude routes in the mountain West - Idaho, Montana, and comparable terrain - ADS-B ground station coverage may be limited at the altitudes the terrain demands. TIS-B in the cockpit may be spotty or absent in those environments. This is not a flaw in the design so much as a real constraint pilots operating in those areas need to factor into their situational awareness.

One critical distinction: the coverage limitation affects ADS-B In reception, not ADS-B Out transmission. If you are not receiving TIS-B traffic, that does not mean ATC cannot see you on radar. Those are separate data paths.

Why Do TIS-B Targets Disappear?

A TIS-B target that vanishes from your display does not necessarily mean the aircraft is gone. Several things can break the relay chain: the aircraft may have changed altitude outside your alert range, moved outside the ground station’s service volume, or descended below radar coverage. A radar facility handoff between facilities can also cause a brief data gap.

This is meaningfully different from an ADS-B Out target going quiet. A direct-broadcast target that stops transmitting has usually landed, powered down, or had an equipment failure. A TIS-B target that disappears may reflect any of those outcomes - or simply a momentary gap somewhere in the relay infrastructure.

What Aircraft Don’t Appear on TIS-B at All?

TIS-B requires a radar return, and radar returns require a transponder. Aircraft operating without transponders - certain experimental aircraft, ultralights, gliders, balloons - generate no radar return and therefore produce no TIS-B target in your cockpit.

This is the more significant surveillance gap. The latency on a TIS-B target is a known, quantifiable limitation. The complete electronic absence of an entire category of aircraft sharing your airspace is a different matter. See and avoid remains the legal and practical foundation of VFR flight. ADS-B In supplements that requirement; it does not replace it.

Understanding FIS-B Weather Latency

FIS-B (Flight Information Service-Broadcast) delivers free weather data through the same ADS-B ground infrastructure: NEXRAD composite imagery, METARs, TAFs, PIREPs, SIGMETs, AIRMETs, TFRs, and NOTAMs - no subscription required.

FIS-B NEXRAD imagery carries its own latency. The FAA specifies a maximum composite image age of 7.5 minutes, but accounting for image generation, broadcast, and receipt, the data on your display can realistically be up to 15 minutes old. Near convective weather, a cell that appears 15 miles from your route may actually be 12 miles out and closing.

The appropriate use of FIS-B weather is strategic awareness, not tactical decision-making near active convection. Garmin GTN and G1000 systems display the weather age explicitly. If you are not checking that timestamp before acting on what you see, you are not working with the full picture your own equipment is providing.

Where Is TIS-B Technology Headed?

The FAA’s surveillance roadmap reflects the radar infrastructure that was already in place when ADS-B was developed. The broader trend is toward space-based surveillance. Aireon’s system, now operational, places ADS-B receivers on the Iridium satellite constellation to capture ADS-B Out broadcasts from aircraft anywhere on Earth - including oceanic airspace where neither ground stations nor radar exist. The FAA, Nav Canada, and other air navigation service providers use this data for oceanic separation.

For domestic airspace, the pressure is not toward more ground stations but toward better data sharing across existing infrastructure. The FAA’s System Wide Information Management (SWIM) program is developing architecture to move surveillance data between facilities closer to real time - in ways that could eventually reduce the latency embedded in TIS-B. Whether that closes the current 6-to-12-second window for cockpit traffic display is an open engineering question. For now, the system operates on the latency it has.

Key Takeaways

• TIS-B targets carry 6–12 seconds of latency, producing up to roughly half a mile of potential position error at 150 knots. Direct ADS-B Out targets carry approximately 2–4 seconds.
• Know your display’s symbology. Garmin typically uses a yellow diamond for ADS-B Out and a white diamond or simplified shape for TIS-B. Other manufacturers differ - check the documentation.
• TIS-B requires both ground station coverage and radar coverage simultaneously. In low-altitude or remote mountain terrain, one or both may be absent - even when your ADS-B Out is transmitting normally.
• FIS-B NEXRAD imagery can be up to 15 minutes old. Use it for strategic weather awareness and check the age timestamp before making decisions near convective activity.
• Aircraft without transponders - ultralights, gliders, balloons, certain experimentals - are invisible to TIS-B entirely. Visual scanning remains the primary separation tool in VFR flight.

Advisory Circular 90-114 covers TIS-B service volumes and performance standards in detail. Aeronautical Information Manual, Chapter 7, Section 1 provides operational guidance on interpreting cockpit traffic information.