ADS-B and Call Sign Confusion

The ADS-B mandate has arrived, and with it comes the potential for another source of confusion. Most pilots flying with ADS-B systems have a display of traffic in the cockpit, either on a moving map that’s part of a GNSS navigation system or on a tablet like an iPad running an app such as ForeFlight, Garmin Pilot, or FlyQ. These traffic systems usually show the identification of other aircraft, either the registration number or the airline flight number.

ADS-B traffic (TIS-B) as shown in ForeFlight

When ATC issues traffic advisories–for example, “Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737”–it might be tempting to include the target identification in your acknowledgement. For example, “Cessna 1234A, we have Southwest 2345 in sight,” or “Southwest 2345 in sight, Cessna 1234A.”

If that sounds odd, watch some aviation videos on YouTube. At least one pilot flying an airplane with a new glass panel has made a habit of such replies.

For obvious reasons, it’s a bad idea to include another aircraft’s identification or call sign when you respond to ATC. In fact, the FAA’s December 2019 update to AC 90-114 Automatic Dependent Surveillance-Broadcast Operations anticipates this issue: Unless initiated by the controller, pilots should typically not use the call sign or Aircraft Identification (ACID) of observed traffic in radio communications, as this could create confusion for both ATC and pilots monitoring the frequency.

AC 90-114B

So even if you’re equipped with the latest technology, stick to the standard replies when ATC points out traffic:

“Cessna 1234A, traffic 2 o’clock, 4 miles, a Southwest 737.”

“Cessna 1234A, we have the Southwest 737 in sight,” or “Traffic in sight, Cessna 1234A.”

New ADS-B Advisory Circular

FAA has updated AC 90-114-Automatic Dependent Surveillance-Broadcast Operations. just as the ADS-B mandate becomes effective at 0001 local time on 2 January 2020.

This advisory circular (AC) provides users of the NAS guidance regarding how to conduct operations in accordance with §§ 91.225 and 91.227. The appendices in this AC provide guidance for additional operations enabled by ADS-B, including ADS-B In…This AC contains an overview of the ADS-B system and general operating procedures in compliance with the airspace and performance requirements of §§ 91.225 and 91.227. The appendices provide guidance on additional ADS-B Out and ADS-B In operations that may be authorized by the Administrator.

The AC provides detailed information about many topics, including:

4.1 General Operating Procedures
4.2 Operator Familiarity of the Installed ADS-B System
4.3 ADS-B Equipment Operations (U.S. Airspace)
4.4 Flight Plans (FP)
4.5 Preflight Requirements (U.S. Airspace)
4.6 Flightcrew Entry of Required ADS-B Data

The AC also discusses issues associated with aerobatic and formation flights, the ADAPT process for applying for exemptions to the ADS-B requirement, and other details not provided in the previous edition.

Flight Information Service (FIS-B): Weather and Info in the Cockpit

Like many pilots, I have long used portable GPS navigators with SiriusXM aviation weather to display NEXRAD, weather reports and forecasts, and TFRs in the cockpit. Having regularly updated (if not truly real-time) information about the weather has been a boon to safety and efficiency, making strategic decisions about weather-related diversions and other changes to the original plan for a flight much less cumbersome.

The introduction of aviation apps for the iPad and other tablets and the completion of the ADS-B ground infrastructure has more pilots using the free Flight Information Service (FIS-B) products that can be integrated into products such as ForeFlight, WingX, FlyQ, and Garmin Pilot–provided you have an ADS-B receiver, such as the Stratus, Garmin GDL 39, or Dual XGPS170, among others.

(SiriusXM has announced a new, stand-alone receiver for its subscription services. It works with the iPad and a dedicated app. Details here.)

SiriusXM and FIS-B: What’s different?

If you’re switching from the satellite-based weather and information services to FIS-B products, it’s important to understand several key differences between the information each provides, and the limitations of the FIS-B services, especially for typical general aviation pilots operating below the flight levels who want to check the weather more than 375 nm ahead.

Of course, it’s also important to understand that SiriusXM information is available even on the ground, assuming the antenna has a clear view of the sky. FIS-B services, based on line-of-sight transmissions from ground stations, typically are available only after you climb at least above pattern altitude; higher minimums often apply. You can view a map of and learn more about ADS-B coverage here.

First, the set of weather reports and forecasts available via FIS-B doesn’t include all of the products from SiriusXM (depending on the subscription plan you choose).

FIS-B includes the following text reports (see AIM 7-1-11):

  • Aviation Routine Weather Report (METAR) and Special Aviation Report (SPECI)
  • Pilot Weather Report (PIREP)
  • Winds and Temperatures Aloft
  • Terminal Aerodrome Forecast (TAF) and amendments
  • Notice to Airmen (NOTAM) Distant and Flight Data Center

FIS-B includes the following products in both text and graphic forms:

  • Airmen’s Meteorological Conditions (AIRMET)
  • Significant Meteorological Conditions (SIGMET)
  • Convective SIGMET
  • Special Use Airspace (SUA)
  • Temporary Flight Restriction (TFR) NOTAM

FIS-B also displays graphical regional and national NEXRAD composite reflectivity information.

Update Schedules

AIM Table 7-1-1 FIS-B Over UAT Product Update and Transmission Intervals shows the intervals at which fresh information is transmitted via the ADS-B network.


Look-Ahead and Altitude Tiers

To avoid overloading the ADS-B transmitters, the amount of information sent to aircraft depends on the altitude of the receiver. The altitude tiers are described in AIM Table 7-1-2 Product Parameters for Low/Medium/High Altitude Tier Radios:


Figure A-2 in AC 00-63A defines the altitude tiers:


Most of us flying normally aspirated, piston aircraft fit into the medium altitude tier, which means that some information (e.g., METARs and TAFs) is available only when the reporting airport is within 375 nm of our present position.

The advisory circular notes that:

Pilots need to consider the performance of the aircraft as well as the update rate for a specific product. For example, a pilot of a light twin aircraft, flying at a medium altitude with a tailwind could easily have a ground speed in excess of 200 knots. Thus, traveling at over 3 NM per minute, a pilot may not have enough time to receive and decipher a pop-up TFR based on the 100 NM look-ahead and a 10-minute transmission interval.

Future FIS-B Products

AC 00-63A notes that FAA plans to add new FIS-B products in June 2018.

For more information about the new products, see this item from AOPA.

These products include:

  • Lightning. Graphical representation of each lightning stroke in a past 5-minute period.
  • Turbulence NOWcast. Two-kilometer resolution grid containing an eight-value turbulence intensity scale in each grid cell. The intensity scale depicts a weighted average turbulence for flight levels (FL) of 10,000 ft and above.
  • Icing NOWcast. Two-kilometer resolution grids, where each grid represents one of the eight 3,000 ft ranges from FL 030 to FL 240. Within each grid, each grid cell contains the four-value icing indication and the presence or absence of Supercooled Large Drop (SLD) formation.
  • Cloud Tops. Two-kilometer resolution grid indicating the altitude of the cloud top to an accuracy of 3,000 ft, ranging from FL 030 to FL 480.
  • One-Minute Automated Weather Observing System (AWOS). More frequent updates of METAR-formatted information.

More Information and Key References

You can find detailed information about FIS-B in the following key references:

In June 2012, NTSB released a Safety Alert about the limitations of NEXRAD displays in the cockpit.

AOPA ASI offers a free online course, IFR Insights: Cockpit Weather, to help you learn more about datalink weather.

Draft AC 90-114A: Automatic Dependent Surveillance-Broadcast Operations

FAA has published a draft update to AC 90-114A: Automatic Dependent Surveillance-Broadcast Operations. It contains useful definitions and references for pilots who want to learn more about ADS-B.

ADS-B Advisory Services: Coverage Essentially Complete in Lower 48

According to the latest maps available from the FAA, the network of ground-based transmitters for ADS-B Broadcast Services (TIS-B and FIS-B) now provides coverage throughout the continental US.

Update: The FAA published a press release on April 14, 2014 announcing the completion of the ground infrastructure, which includes 634 radio stations.

The following diagram shows the locations of the operating transmitters as of late March 2014.


And here’s a diagram that shows the coverage provided by the network. Note that these service volumes assume you are high enough to receive the broadcasts, typically at or above about 1,500 feet AGL, depending on your distance from a transmitter.


Here’s an FAA video that describes ADS-B Broadcast Services.

ADS-B Coverage Map Expands

Sporty’s Pilot Shop has published an updated ADS-B coverage map. The holes in the ADS-B ground network are filling in. You can read the background information at Sporty’s iPad Pilot News, here.