Traffic Information Service (TIS) – Aviation Safety

Introduction

The Traffic Information Service (TIS) represents a significant advancement in aviation safety, offering pilots real-time awareness of nearby air traffic. Developed to support the “see and avoid” principle, TIS bridges the gap between traditional visual scanning and sophisticated electronic surveillance, particularly in the U.S. National Airspace System (NAS) and other modernized airspaces worldwide.

TIS is not a replacement for collision avoidance systems but serves as a vital advisory layer, supplementing pilot vigilance with timely, relevant traffic data—especially valuable during high workload, limited visibility, or congested airspace operations. This glossary entry provides a comprehensive overview of TIS, including its operational principles, technologies (TIS-A and TIS-B), integration with other surveillance systems, limitations, and best practices for pilots and fleet operators.

What is Traffic Information Service (TIS)?

Traffic Information Service (TIS) is a ground-based, surveillance-driven tool that relays real-time data about proximate aircraft to pilots in the cockpit. Its core function is to enhance situational awareness by transmitting the position, altitude, heading, and relative movement of surrounding air traffic. Unlike airborne collision avoidance systems (like TCAS), TIS is strictly advisory and relies on pilots to visually confirm and react to traffic.

TIS information originates from ground radar stations and, in the case of TIS-B, is augmented with ADS-B (Automatic Dependent Surveillance–Broadcast) data. This information is then uplinked or broadcast to suitably equipped aircraft, where it is displayed on dedicated or integrated cockpit displays. The system is especially vital in “mixed-equipage” airspace, where not all aircraft are equipped with the same level of surveillance technology.

TIS-A (Traffic Information Service – Advisory)

How It Works

TIS-A is the original implementation of TIS, built upon Mode-S radar technology. Mode-S radars interrogate aircraft transponders (specifically Mode-S transponders), collect positional and altitude data, and then uplink this information to requesting aircraft. The uplink occurs at regular radar sweeps—typically every 4.8–5 seconds in terminal areas.

To ensure relevance, TIS-A uses predictive algorithms to estimate aircraft positions at the time the data is displayed, accounting for the inherent delay between radar interrogation and cockpit update. The transmitted traffic data includes:

• Range and bearing of proximate aircraft
• Relative altitude (+/- feet)
• Direction of flight (track or heading)
• Trend arrows indicating ascent/descent or closing/opening

Coverage and Limitations

TIS-A coverage is limited to terminal areas equipped with participating Mode-S radars. Not all Mode-S ground stations support TIS uplinks, and coverage may be restricted by terrain or altitude. Only transponder-equipped aircraft (Mode-A, Mode-C, or Mode-S) are visible to TIS-A clients; non-transponder aircraft remain invisible.

TIS-A is strictly advisory. It does not provide conflict resolution or maneuvering instructions and should not be used alone for separation or avoidance. Pilots must visually acquire and confirm targets before maneuvering.

TIS-B (Traffic Information Service – Broadcast)

NextGen Surveillance

TIS-B was developed as part of the NextGen airspace modernization initiative, leveraging the widespread adoption of ADS-B infrastructure. TIS-B fuses data from multiple ATC radar sources—including primary radar and secondary surveillance radars (ASR, ARSR)—and rebroadcasts this data via ADS-B ground stations to aircraft equipped with ADS-B In receivers.

How TIS-B Works

When an ADS-B In-equipped aircraft enters TIS-B service volume, the ground infrastructure forms a “hockey puck”—a 30 NM diameter, ±3,500 ft altitude volume centered on the aircraft. Radar-detected traffic within this volume is broadcast to the client aircraft, supplementing direct ADS-B air-to-air traffic data.

• TIS-B traffic includes non-ADS-B aircraft detected by radar (Mode-A/C/S transponders).
• The system correlates, filters, and predicts traffic positions to minimize clutter and maximize relevance.
• Update rates vary (from ~3 seconds for ASR to 13 seconds for ARSR), less frequent than airborne systems like TCAS.

Coverage and Advantages

TIS-B provides broader coverage than TIS-A, including en-route and terminal airspace wherever ADS-B ground stations and radar coverage exist. It is especially valuable in mixed-equipage airspace, ensuring that pilots with ADS-B In can still see non-ADS-B Out targets detected by radar.

As with TIS-A, TIS-B is advisory only. Visual acquisition remains imperative.

ADS-B (Automatic Dependent Surveillance–Broadcast)

ADS-B forms the backbone of modern air traffic surveillance:

• ADS-B Out: Aircraft transmit their position, velocity, and identification to ground stations and other aircraft.
• ADS-B In: Aircraft receive ADS-B messages, including TIS-B and ADS-R (Automatic Dependent Surveillance–Rebroadcast), directly from ground stations and other aircraft.

ADS-B operates on two main frequencies:

• 1090ES (1090 MHz Extended Squitter): Standard for high-performance and commercial aircraft, required above FL180 in the U.S.
• UAT (978 MHz Universal Access Transceiver): Used mainly by general aviation below FL180 in the U.S., also supports FIS-B (in-cockpit weather and information).

ADS-B data includes performance parameters (NACp, NACv, SDA, SIL, NIC) to verify position accuracy and integrity. Proper configuration ensures participation in TIS-B and other ADS-B services.

Mode-A/C/S Transponder

A Mode-A/C/S transponder is an aircraft device that responds to radar interrogations:

• Mode-A: Four-digit squawk code for identification.
• Mode-C: Adds encoded altitude reporting.
• Mode-S: Enables selective interrogation, data link, and compatibility with TIS-A and ADS-B.

Mode-S is essential for TIS-A clients and supports extended squitter (ADS-B Out). Aircraft with only Mode-A/C can still be detected by radar and included in TIS-B traffic for nearby ADS-B In-equipped aircraft.

Transponder reliability, correct coding, and maintenance are crucial for effective participation in TIS and ATC surveillance.

Cockpit Display of Traffic Information (CDTI)

A CDTI is an avionics interface (often integrated into a multi-function display) that presents real-time traffic data to pilots, sourced from TIS-A, TIS-B, or direct ADS-B In. Key features include:

• Graphical representation of nearby traffic (bearing, range, relative altitude)
• Trend vectors, closure rates, and traffic advisories
• Overlay with moving maps, terrain, and weather (where supported)
• Customizable symbology and orientation (track-up, north-up, etc.)

Effective use of CDTI depends on display clarity, pilot training, and understanding system limitations.

TIS-A vs. TIS-B

Both systems are advisory and not for primary collision avoidance. TIS-B is preferred in modern, mixed-equipage airspace.

Surveillance Update Rate

Surveillance update rate is the interval between data refreshes:

• TIS-A: ~5 seconds (Mode-S radar sweep)
• TIS-B: 3–13 seconds (ATC radar dependent)
• TCAS/TAS: 0.5–1 second (airborne system)
• ADS-B Air-to-Air: ~1 second

Longer update rates can result in outdated (“ghost”) targets, especially during rapid maneuvers. Pilots must understand this lag when interpreting traffic displays.

ADS-B Link Technologies: 1090ES and UAT

• 1090ES: International standard, mandatory for high-altitude/commercial operations. Interoperable with Mode-S and TCAS.
• UAT: U.S.-only, general aviation, supports weather (FIS-B) and traffic (TIS-B, ADS-R). Used below FL180.

Both are supported by TIS-B/ADS-R ground stations, ensuring broad accessibility for equipped aircraft.

ADS-B Performance Parameters: NACp, NACv, SDA, SIL, NIC

• NACp: Position accuracy
• NACv: Velocity accuracy
• SDA: System design assurance (probability of erroneous data)
• SIL: Source integrity level (undetected errors)
• NIC: Navigation integrity containment (radius of uncertainty)

ADS-B systems must meet minimum standards for these parameters to ensure their data is used for surveillance and TIS-B.

Mixed-Equipage Airspace

Mixed-equipage airspace is where aircraft with varying levels of surveillance equipment (ADS-B, Mode-S, Mode-A/C, or none) operate together. TIS-B is designed to bridge surveillance gaps by sharing radar-derived traffic with ADS-B In users. However, non-transponder aircraft remain invisible, requiring continued visual vigilance and adherence to “see and avoid.”

TIS-B Service Volume (“Hockey Puck”)

The TIS-B service volume is a moving, cylindrical area (30 NM diameter, ±3,500 ft) centered on each ADS-B In client. Only radar-detected aircraft within this volume are included in TIS-B broadcasts to minimize clutter and maximize relevance.

Regulatory and Operational Considerations

TIS and associated systems are governed by FAA, ICAO, and national standards, including:

• ICAO Annex 10 (Aeronautical Telecommunications)
• FAA Advisory Circulars and Technical Standard Orders (TSOs)
• National mandates for ADS-B equipage and performance

Operators must ensure proper installation, certification, and pilot training for all surveillance and display systems.

Best Practices for Pilots

1. Understand System Limitations: TIS is advisory; always visually acquire targets before maneuvering.
2. Maintain Equipment: Ensure transponders and ADS-B systems are correctly configured and maintained.
3. Monitor Surveillance Update Rate: Be aware of possible lags in displayed traffic.
4. Use CDTI Effectively: Integrate electronic displays with visual scanning.
5. Stay Informed: Keep current on regulatory changes, airspace mandates, and equipment upgrades.

Frequently Asked Questions

What is the purpose of Traffic Information Service (TIS) in aviation?

TIS enhances situational awareness by providing real-time advisory traffic data to pilots, helping them identify and monitor proximate aircraft and supporting safe, efficient operations—especially in busy or mixed-equipage airspace.

How do TIS-A and TIS-B differ?

TIS-A uses Mode-S radar for direct uplinks in limited areas, while TIS-B fuses radar and ADS-B data, broadcasting a broader traffic picture to ADS-B In-equipped aircraft across much wider regions.

What equipment is needed for TIS?

TIS-A requires a Mode-S transponder and compatible cockpit display. TIS-B requires ADS-B In equipment. Both depend on ground infrastructure coverage and proper aircraft installation.

Is TIS a collision avoidance system?

No. TIS is advisory only; pilots must visually identify targets before maneuvering and should combine electronic displays with visual scanning.

What are TIS limitations?

Coverage is limited by ground radar and ADS-B infrastructure, and only transponder-equipped aircraft are displayed. Update rates can introduce display lag, and non-transponder aircraft remain invisible.

Conclusion

Traffic Information Service (TIS) is a vital tool in the modern pilot’s situational awareness arsenal. By leveraging radar and ADS-B infrastructure, TIS (through TIS-A and TIS-B) provides timely traffic data, supports “see and avoid,” and helps bridge the surveillance gap in mixed-equipage airspace. Pilots and operators should understand system capabilities, limitations, and regulatory requirements to maximize the safety benefits of TIS.

For more information about integrating TIS or upgrading your fleet’s surveillance capabilities, contact our aviation safety experts or schedule a demonstration .