Transponder and ADS-B Requirements

Transponders are required to be inspected by an FAA Certified Repair Station every 24 calendar months according to FAR 91.413 in accordance with FAR 43 Appendix F. If you have an altitude encoder interfaced to your transponder, the correlation must be checked with your altimeter at the same time according to FAR 91.411 in accordance with FAR 43 Appendix E Part c. Other information on altitude reporting systems can be found in FAR 91.215, 91.217 and AC 43-6C.

Even if you only fly VFR your transponder, encoder/altimeter correlation, and pitot/static system still must be checked by Federal Law. Anytime your transponder is in the ALT position, it will be sending signals to air traffic control, as well as, other aircraft with traffic advisory systems telling them your altitude. If you don't have the altimeter/encoder coorelation checked, your transponder may be sending them incorrect altitude information. This should be correct for the safety of everyone under air traffic control and flying with traffic advisory systems. In addition to the above, to fly in IFR conditions, the altimeter must be recertified according to FAR 91.411 in accordance with FAR 43 Appendix E.

The following refers to non-charter general aviation aircraft. ADS-B Out will be required January 1, 2020 for aircraft that will be flying into Class A (18,000 ft and above), Class E (10,000 ft to 17,999 ft), Class B or above (Very Large Airports), Class C or above (Large Airports) airspace and into 30nm Mode C rings. ADS-B Out will also be required when flying within 12nm and at or above 3000 feet MSL off the US shore in the Gulf of Mexico. ADS-B Out will not be required in Class E (10,000 ft to 17,999 ft) airspace IF you stay below 2,500 feet AGL, for example flying over mountains. ADS-B Out will not be required to fly into Class D airspace or uncontrolled airfields, as long as they are not located within a 30nm Mode C ring and you stay out of Class B and Class C airspace. To clarify, you will not be able to fly above Class B or Class C airspace either without ADS-B Out. See picture below.

If your aircraft was not originally certified with an electrical system, you are not required to install ADS-B Out. That being said, there are approximately 87,000 flights in the US per day. ADS-B Out gives ADS-B In equipped aircraft traffic information on their position, altitude, climb/descent and direction of flight. This makes the aviation community much safer.

With ADS-B In you would receive traffic and weather information for free right now! FAR 91.225 is the rule on ADS-B Out equipment. ADS-B Out requires a WAAS GPS positioning source. Unless you currently have a compatible WAAS GPS, your GPS cannot be used for ADS-B Out positioning. In that case, you would have to go with an all inclusive ADS-B system which has a built-in WAAS GPS receiver, display/controller and a WAAS GPS antenna would have to be mounted on top of your aircraft.

There are two options: Mode S Transponder with internal WAAS GPS and ADS-B Out transmitting 1090ES or UAT with internal WAAS GPS and ADS-B Out transmitting 978. 1090ES will be required in Class A (18,000 ft and above) and meets the mandate for all airspace. In all other airspace (below 18,000 ft), a UAT which transmits on 978MHz would suffice. The best long term option is the Mode S Transponder because you are replacing your old transponder with new one, they contain a solid state transmitter and utilize one transponder/ADS-B Out antenna. With the UAT, you are adding a whole new system to your aircraft, you must keep your existing Mode C Transponder and add another ADS-B Out antenna on the bottom of your aircraft. In several aircraft, UAT's must be mounted in the rear avionics bay and wiring run to the front of the aircraft for interfacing to power, existing equipment and display units, which means more labor and parts. Your old transponder, more than likely, contains a cavity tube transmitter. This is the most expensive part in an old transponder and if it goes bad would cost $1,000.00 or more to repair, if it can be repaired at all. If it cannot be repaired, you will be installing another used transponder or a new one.

FAR 91.217 states that an ADS-B UAT must receive the same altitude reporting information as the transponder. So, the same encoding altimeter, blind altitude encoder or air data computer must be interfaced with the transponder and a UAT ADS-B Out unit. Replacing an old altitude encoder that has 9 wire grey code and 100 ft resolution with a new altitude encoder that uses single wire RS232 and 10 ft resolution is a good idea at the time of your ADS-B installation. They are fairly inexpensive, around $300.00, and actually easier to install with the single wire RS232 data. They give ATC and other ADS-B In equipped aircraft 25 ft resolution of your altitude.

Several ADS-B Mode S Transponders and UATs provide the option of ADS-B In. They will display on various WAAS GPS units, Multi-Function Displays and iPad Pilot Apps.

Lafayette Avionics, Inc. is a full service avionics facility, FAA Certified Repair Station with Class I, II, III, limited instrument, and limited airframe ratings, that can perform the required transponder and altitude reporting inspections for you. We can also install ADS-B in your aircraft.

Give us a call at (765) 743-3828 for information on all your avionics needs.

Email us at:  josh@avionics-laf.com

Hoping we can be of service, Ron and Josh

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