UPDATE

5/9/2018

Bendix/King, L3 and ACSS released the NXT-700/MST-70B as form fit replacement for the MST-67A. It is DO-260B compliant to meet the ADS-B Out mandate.

There are other options besides the MST-70B to gain ADS-B compliance. There are various STCs that allow the removal of the Bendix/King transponder system and installation of Rockwell Collins or Garmin transponders. Upgrade prices vary depending on actual installed equipment. 

Regarding ADS-B for the Garmin GTX-330 transponders, the best solution is to simply have the units converted by Garmin to include the ES (Extended Squitter) upgrade. This upgrade is about $2000 approximately. Additionally, a WAAS/GPS source will need to be interfaced. We can process the upgrade for you or any other Garmin dealer can as well.

Extended Squitter (or 1090 ES) is the Mode S transport protocol for ADS-B operation. 1090 MHz extended squitter is an ADS-B link for air carrier, commercial, and private aircraft. With 1090ES, the Mode S transponder supports an extended squitter (ES) message. Currently, this message provides position, velocity, and heading information.

The ES versions of the Garmin GTX33, GTX-330, and GTX-330D transponders comply with FAA TSO C-166A which dictates the minimum performance standards (MPS) for 1090 MHz ADS-B equipment. Existing Garmin GTX Mode S transponders without ES can be upgraded through Garmin to include the Extended Squitter feature. On average the Extended Squitter option costs an additional $1000-$1500 USD.

It is very important to note that in order for the ES data to be broadcasted, the transponder must be interfaced to a compatible GPS that meets TSO C145a/C146a. These TSOs explains the performance standards for WAAS GPS receivers. As of 2009, the CNX80, GNS480, GNS400W/500W series and G1000 are the only Garmin GPS receivers that meet this criteria.

Utilizing more than one antenna to improve the quality and reliability of radio signal is called antenna diversity.

Heavy and/or faster aircraft utilize top and bottom antenna configurations to eliminate the possibility of signal blind spots caused by shadowing. Lighter, slower general aviation aircraft typically only have 1 antenna and do not require antenna diversity. Although not completely uniform, the transmission pattern of a typical antenna provides adequate radiation above and below in relation to most GA aircraft even when the antenna is on the bottom of the aircraft.

The Mode S aircraft identification code is listed on AC Form 8050-3, Certificate of Aircraft Registration, as the International Civil Aviation Organization (ICAO) Aircraft Address Code. If the aircraft registration does not contain this information, aircraft owners with a Mode S transponder can obtain an aircraft identification code from the FAA Aircraft Registry in Oklahoma City, Oklahoma. This may be accomplished by writing to the following FAA address:

Federal Aviation Administration
Aircraft Registration Branch AFS-750
P.O. Box 25504
Oklahoma City, OK 73125-0504

You may also call:
866-762-9434
405-954-3116

Newly Overhauled parts obtained from Garmin are designated with an N in their part number. This usually follows the 010- in the part number. As with most Garmin 010 part numbers, the N part numbers are for ordering purposes only and do not actually appear on the dataplate of the unit.

In relation to the transponder technology, a squawk refers to a response that a transmitter responder (i.e. transponder) is making to an interrogation from Air Traffic Control (ATC). In a classic Mode A/C transponder, a squawk response included very basic aircraft ID, general status, and pressure altitude information.

A squitter or squit is a transmission that frequently sends aircraft ID and position data while not being interrogated. In some Mode S transponders and ADS-B devices, the squit transmission can include up to almost 50 parameters including lat/long position, direction of flight, velocity, and more.