There are approximately 19 pieces of information that your ADS-B is required to transmit through the entire operation – both during flight and while taxiing.  Per 14 CFR 91.227 and 91.225, each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times, unless authorized by the FAA or directed by air traffic control (ATC).
FAA inspectors expend many staff hours contacting owners/pilots of aircraft known to have ADS-B systems that are either not broadcasting or are broadcasting incorrect information.

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Do not rely on ATC to advise you that your ADS-B is inoperative. ADS-B Out systems are required to indicate a failure to the pilot, per FAA AC 20-165 (ADS-B Installation guidance).
You should know that your ADS-B system has two major components, either of which could fail:

• ADS-B transmitter
• Position source (GPS or WAAS)

Your ADS-B installation documents or Pilots Operating Handbook should tell you how to recognize whether your ADS-B has failed (device failure) or the GPS input to your ADS-B has failed (function failure). Some installations use the existing transponder fail light, while others have a dedicated indicator.  Major ADS-B manufacturers including Garmin, L3Harris, and FreeFlight have confirmed to the FAA that their products comply with the annunciation requirements.

Below are the relevant portions of AC 20-165B, Airworthiness Approval of Automatic Dependent Surveillance - Broadcast OUT Systems

• 3.7.2.1.1 ADS-B Device Failure
  • If the ADS-B equipment is unable to transmit ADS-B messages, the system should provide an appropriate annunciation to the flight crew.


• 3.7.2.1.2 ADS-B Function Failure
  • The ADS-B system depends on a position source to provide the data to populate the ADS-B messages and reports. If the position source or its interface with the ADS-B equipment fails, the ADS-B system will not be able to broadcast the required ADS-B data. In this case, the ADS-B equipment has not failed, but it cannot perform its function due to a failure to receive the position source data. The ADS-B system should distinguish between a position source or interface failure and an ADS-B equipment failure. The installer must provide documentation, in the applicable flight manual, or flight manual supplement, that explains how to differentiate between annunciation of an equipment failure and a function failure if the failure annunciations are not independent.

Please note: Technical challenges associated with the device failure and function failure may exist when installing a Universal Access Transceiver (UAT) on aircraft with only a Mode C transponder. However, most manufacturers still include those failure annunciations in their UAT products.

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Failure indications do not tell the whole story.  The ADS-B rule has a performance component specified in 14 CFR 91.227.  Because of its many inputs, it’s possible for your system to not indicate a failure, yet still not be performing correctly.

You can determine if your ADS-B Out system is meeting rule performance requirements by requesting a free Public ADS-B Performance Report (PAPR).

Requesting a PAPR is the best and easiest way to check that your equipment is meeting all the requirements of 91.227.  You can request a PAPR as often as you like, after any flight.

The FAA recommends that aircraft owners and operators check their equipment’s performance after installation and periodically afterwards, particularly after any aircraft maintenance is performed, since avionics performance can change over time.

For more information on how to check your ADS-B performance, please view the virtual PAPR seminar.

Please note:  The FAA discourages pilots from contacting Air Traffic Control to verify the operational status of their ADS-B.  Asking a controller creates unnecessary frequency congestion and distracts them from their primary task of safe separation of traffic.  Also, while the ATC system uses your ADS-B Out information for tracking, by design it only makes available the information controllers need for the purpose of air traffic separation -- they do not have the information to determine that all aspects of your ADS-B are functioning in compliance with FAA regulations.

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It’s important to know how your ADS-B is powered and how to turn it on/off.  This will help your awareness of whether or not your ADS-B system could be inadvertently disabled.

For example, in UAT installations powered by external aircraft lights, the pilot controls whether or not power is applied to the ADS-B system.

The FAA recommends adding a preflight checklist item to ensure that your ADS-B system is turned on for every flight – day or night, regardless of the airspace you plan to fly in.
Please note: In accordance with § 91.225(f), each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times, unless authorized by the FAA or directed by air traffic control (ATC).

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Per 14 CFR 91.227(d)(8) requirements, you must ensure that the flight ID broadcast by your ADS-B Out equipment exactly matches the aircraft ID (call sign) used on the flight plan. If the ADS-B flight ID does not exactly match the aircraft ID provided on the flight plan, it creates a Call Sign Mismatch (CSMM) event. CSMM mitigation efforts by air traffic controllers, especially in busy airspace, can lead to significant operational difficulties, including distraction, increased frequency congestion, and increased workload.

To avoid Call Sign Mismatch, the FAA recommends the following:

1. Verify that your flight ID is set correctly by requesting a PAPR Report after your ADS-B Out system is installed and/or repaired.  It’s also a good idea to request a PAPR report after purchasing a new, ADS-B equipped aircraft.
2. For ADS-B Out transmitters with a pilot-changeable flight ID, have a standard procedure for checking that the correct flight ID is entered prior to taxiing.
3. If your organization assigns you an ICAO three letter flight ID for a particular mission (i.e. Angel Flight), be sure the flight ID is entered correctly in the ADS-B prior to taxiing and remember to change the flight ID back to the “N number” after the mission is completed.
4. Always verify that the ADS-B flight ID is correct after any maintenance activity, especially when the battery is disconnected, as this activity may reset the flight ID field. The easiest way to verify this is by requesting a PAPR Report. 

For more information on Call Sign Mismatch, please view the virtual CSMM seminar.

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