ADS-B Out vs. ADS-B In: What’s the Difference?

Since there’s less than a year until the requirement (14 CFR § 91.225) for all aircraft to be equipped with Automatic Dependent Surveillance-Broadcast (ADS-B) Out when operating in US airspace that requires the use of a transponder (don’t throw that out, ADS-B doesn’t replace your transponder yet!), I thought it might be useful to have another look at ADS-B Out and In, and what it means to us as pilots.

The “I’m on short final and don’t have time so give me a quick summary” version:

  • ADS-B Out uses data obtained from your aircraft’s WAAS-enabled GPS receiver to broadcast your position, speed, and altitude, along with your aircraft ID.
  • ADS-B In does the same thing as ADS-B Out plus it also allows you to receive real-time traffic and weather information on your aircraft cockpit display, or your iPad/tablet if you have it linked by Bluetooth to your ADS-B In and are using an app like ForeFlight or Garmin Pilot.

The “I’m in the cruise and have run out of movies” version:

 ADS-B is a part of the FAA’s Next Generation Air Transportation System, or NextGen, their plan to modernise US airspace with the integration of new technologies, making flying safer and more efficient. ADS-B Out performs a similar function to what transponders currently do; however, instead of waiting for an interrogation pulse from a secondary surveillance radar or TCAS before it replies with its altitude (if selected) and squawk code, ADS-B Out will effectively continuously transmit your aircraft ID, position, speed, and altitude. This will allow air traffic controllers and other participating aircraft to use that information to improve situational awareness leading to reduced separation standards, safer operations, and more direct flight routes saving operators time and money.

Components. Source: faa.gov

There are four basic components that make ADS-B possible, two in your aircraft and two external:

  • GPS + WAAS satellite constellations
  • Ground stations
  • WAAS-enabled GPS receiver
  • 1090ES ADS-B system (required above FL180) or a UAT ADS-B system

Note: even though your aircraft requires a WAAS-enabled GPS receiver for ADS-B Out to work, that doesn’t mean you need a glass cockpit or a GPS such as a Garmin 430W. You would, however, need a cockpit display or an iPad/tablet to use the ADS-B In functionality, which we’ll get to next.

ADS-B In

ADS-B In provides the same data transmitting functionality of the ADS-B Out system, with the bonus of being able to receive Traffic Information Service-Broadcast (TIS-B), and, if your aircraft is equipped with a 978MHz Universal Access Transceiver (UAT), Flight Information Service-Broadcast (FIS-B); both are free services transmitted automatically to your aircraft. FIS-B includes the following:

  • Aviation Routine Weather Reports (METARs)
  • Non-Routine Aviation Weather Reports (SPECIs)
  • Terminal Area Forecasts (TAFs) and their amendments
  • NEXRAD (regional and CONUS) precipitation maps
  • Notice to Airmen (NOTAM) Distant and Flight Data Centre
  • Airmen’s Meteorological Conditions (AIRMET)
  • Significant Meteorological Conditions (SIGMET) and Convective SIGMET
  • Status of Special Use Airspace (SUA)
  • Temporary Flight Restrictions (TFRs)
  • Winds and Temperatures Aloft
  • Pilot Reports (PIREPs)

Obviously, FIS-B is a great tool for us pilots, there is one catch with the FIS-B service though.. Because it is only available on UAT systems, you won’t be able to use the service if you are flying an aircraft that is equipped with a 1090ES system (which is required on all aircraft that will operate above FL180). Here’s a helpful graphic from the FAA depicting the airspace requiring ADS-B from 1 January 2020:

Airspace Requirements. Source: faa.gov

Hazards of ADS-B In

Whether you’re like me and you spend most of your time flying a bug smasher around, or you fly something a little fancier, the added functionality provided by ADS-B In is a huge bonus! I’ve found that the traffic information service alone is extremely useful when flying around in the training area with students, as it really helps to improve situational awareness and safety. As with most new cockpit technologies though, there are a couple of hazards we must look out for:

  • Complacency – just because our cockpit display or iPad now shows other traffic also using ADS-B, doesn’t remove our obligation to maintain vigilance to see and avoid other aircraft (especially ones that may not be using ADS-B), by keeping a good lookout.
  • Distraction – make sure to learn how to use your ADS-B and associated cockpit displays before you go flying, keep your scan up, and avoid task fixation. Remember, fly the aircraft first.

Conclusion

On 1 January 2020, ADS-B Out will be legally required for all aircraft operating in US airspace that requires a transponder. ADS-B In is a fantastic tool that will additionally provide your aircraft with real-time traffic and weather information that can greatly improve safety and situation awareness if used correctly, but we need to guard against complacency and distraction.

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