There are many hidden issues that need to be considered about Flight Management Systems (FMS) before you take the steps to become ADS-B compliant.
Currently there are two categories of FMS and GPS solutions: those certified to meet the requirements of TSOC129a/b for older GPS, non-precision approach, and those that are certified for WAAS. Both provide adequate position accuracy for current flight regulations; however not all are able to meet the new ADS-B mandate requirements.
Older C129a/b FMS/GPS systems do not provide high-precision approach information and are not accurate enough to meet the ADS-B mandate requirements. The FAA will provide the requirements to the OEMs, but it is highly unlikely that manufactures will recertify these units to meet the new requirements or modify their receivers to put out the required format of position data.
WAAS-certified FMS/GPS meet the high-precision accuracy requirements, but when OEMs designed these, they did not include the outputs necessary to feed the transponders.
To bridge this gap, the FAA is planning on releasing an additional TSO to the manufactures with guidance or specifications to design a “patch” to meet the ADS-B mandate requirements. FAA has not released a second advisory circular that discusses the mandate for patch TSO. Manufacturers won’t begin work until this is released.
IMPORTANT TO NOTE: This new patch TSO from the FAA is only part of the overall process in getting an aircraft certified asADS-B out certified.
The biggest problem an operator will face with this mandate will be waiting for the industry OEMs to catch up with solutions to their aircraft.
For more information about ADS-B, download "Straight Talk About ADS-B" at www.DuncanAviation.aero/straighttalk. Or feel free to contact our avionics experts with your questions and challenges when the subject of ADS-B arises.
Mark Winter serves as the Satellite Avionics Manager for the Houston, Texas avionics shop, specializing in avionics modification and full line maintenance. He began working in aviation in 1988.