The ABC's of the ADS-B Mandate

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By Bill Forbes
Director of Avionics Sales – Elliott Aviation

Understanding the reason why and what needs to be done will lessen the confusion about the ADS-B OUT mandate for the U.S

What is ADS-B?
The easiest way to understand Automatic Dependent Surveillance-Broadcast or ADS-B, is that it is a way for aircraft to send additional data in order for air traffic to route aircraft more safely and efficiently throughout controlled aerospace in the United States. As part of the NextGen air traffic control (ATC) system, data such as altitude, airspeed, and heading are transmitted through an aircraft’s transponders. In order to send this data, transponders either need to be updated or already capable of complying with the mandate. These transponders then take input from a WAAS GPS receiver, which is required for position accuracy, and transmit the data back to ATC.

Factory Upgrade Path for ADS-B
While many legacy aircraft operators only want to meet the mandate and don’t want to make more upgrades, many factory upgrades will require expensive updates. Aircraft operators can choose a factory upgrade path for a legacy aircraft or decide to completely replace their transponders, which could be more cost-effective for the operator, such as Elliott Aviation’s Garmin GTX-3000 ADS-B solution. All aircraft equipped with factory original transponders will need an upgrade to a WAAS GPS. In most cases, the GPS is located in the Flight Management System, which will require an upgrade that could require an expensive LPV upgrade. In addition, there may be other unexpected costs when sending in your transponders for modification to satisfy the upgrade path. In several cases, when legacy units have been sent in for modification, they have found costly repairs that have cost operators tens of thousands of dollars.

Most turbine-powered aircraft have two transponders, with one used for redundancy. The most widely used transponder in the population of turbine-powered business aircraft is the Rockwell Collins TDR-94/D. Depending on age, TDR-94/D can be upgraded, but you may have to buy new TDR-94/D transponders if they are too old. Other popular transponders include the Honeywell RCZ-8XX series and the BendixKing MST-67/A. The RCZ series of transponders can be sent in to be upgraded, but older transponders may need to be replaced, much like the TDR-94. The BendixKing MST-67/A transponders do not have an upgrade. The solution from BendixKing is to provide a new transponder called the Honeywell MST-100. These legacy transponders were typically designed in the late ’80s and early '90s when electronic technology was more hardware-driven than computer software-driven. Remember the late ’80s and early ’90s was when the Apple II computer was king.

Flight ID
ADS-B in the United States requires a Flight ID that can be one of two options. It can be an assigned flight number or the aircraft registration number. Most business aircraft use a registration number for filing flight plans. ADS-B Flight ID transmissions and your filed flight plan have to match, or the FAA will send you an ADS-B non-compliance letter. Why is this important? To input your flight ID in a Rockwell Collins, Honeywell, or BendixKing system, you need a control head that is capable of entering it and sending it to the transponder. Most of these legacy avionics packages don’t have this ability, so in addition to the cost of upgrading your Transponders and GPS, you have to update or buy new control heads.

A Better Transponder
A better and likely more cost-effective alternative to the old Collins or Honeywell transponder comes from Garmin. The Garmin GTX-3000 solution provides you with one upfront fixed cost without the hassle and unexpected cost of updating an FMS or control heads. In contrast to competing transponders, the GTX-3000 transponder was designed in the mid-2010s with current technology and built to meet the needs of Part 23 & Part 25 turbine-powered aircraft. In addition, this fit-all transponder makes it, so you don’t have to update your FMS, saving you additional money during the ADS-B out mandate. Paired with a dedicated WAAS GPS receiver, you get added benefits of receiving ADS-B in, which gives you graphical weather and traffic on a Bluetooth-connected device.

This software-driven transponder can easily be software programmed to adapt itself to completely mimic and replace a TDR-94/94D or MST-67/67A. In an RCZ, the GTX-3000 replaces the function of the transponder only and leaves the comm functionality. In addition, the GTX-3000 transponder saves you time and money because you don’t have to update your control heads. It will allow you to store your aircraft registration number, so upgrades or replacement of the transponder control head is not required. This solution can be installed at any Garmin Aviation dealer in the world that is capable of working on Part 23 & Part 25 aircraft like the Hawker 800A/XP, Hawker 1000, Premier 1/1A, Beechjet 400A, Lear 45 & 60, King Air series, Citation Excel/XLS, Citation V/Ultra/Encore, IAI Astra, Falcon 50/900, Challenger 600/601/604 and many, many more.

As of this writing, in November of 2018, there have been supply issues for most avionics manufacturers. This has caused delays in receiving new equipment and delays in updates to GPS receivers and Transponders. Garmin has remained relatively immune to long lead times by controlling the assembly process in Olathe, Kansas, along with producing equipment to meet current and future demand. That is one reason why Garmin ranks #1 in reader polls.

Approving an ADS-B Solution
The FAA has made the process of approving ADS-B solutions simple and streamlined. Initially, a matched pair between a transponder and WAAS/GPS receiver needs to be approved under FAA STC/TC or Aircraft Service Bulletin. To simplify the approval process and help aircraft operators, the FAA has issued a statement that when an STC is approved for a matched pair; it can be used on another make and model of aircraft with the same matched pair and does not need to be Field Approval by the local FAA FSDO. They state the make/model difference as a minor deviation as referenced under AFS-360-2017-1, found here. What they do require, however, is a full copy and authorization from the STC owner. Any deviations deemed major (i.e., penetration to the pressure vessel, antenna mounting, pressure bulkhead penetrations, etc.) will need approval by the FAA or preferably an FAA DER.

Final Thoughts
The magnitude of the ADS-B mandate is unlike anything we’ve ever experienced in this industry. The volume of aircraft that need to be updated and the mix of different legacy avionics packages currently equipped in part 25 aircraft has created a lot of confusion in the industry. There are many factors to consider when selecting an ADS-B solution, like price, anticipated length of ownership, and downtime. A reputable avionics facility can present you with options that will consider your aircraft needs.

Find out more about ADS-B here.

About the Author
Bill Forbes is an Avionics Sales Manager for Elliott Aviation. Bill has been with Elliott since 2018. He started his career in aviation as a crew chief in the Air Force in 1985. He has been associated with Beechcraft Aircraft and Service Centers since 1996. He has been involved in avionics sales and management since 2003 and has been involved in several STC projects with Collins, Honeywell, and Garmin prior to joining Elliott Aviation. You can reach him at