What’s the Frequency Kenneth?
One of the biggest questions when looking at ADS-B is 978 or 1090 — megahertz (MHz) that is. As part of the ADS-B rule, the FAA allowed two different ways to meet the ADS-B Out requirement if you always fly below 18,000 feet MSL. One was a 978 MHz Universal Access Transceiver (UAT) and the other is the 1090 MHz Extended Squitter (ES).
Originally, UAT was envisioned to be the GA solution for ADS-B. UAT is still a perfectly acceptable solution for anyone who flies below 18,000 feet MSL and within the United States. UAT operates in addition to your existing Mode C transponder (which is still required in 2020), essentially adding ADS-B to your current set up. Some UAT systems have the advantage of being slightly less expensive for the hardware, although the Aircraft Owners and Pilots Association (AOPA) notes that they are sometimes more expensive to install. UAT might be the “easiest” solution to add to an existing setup.
UAT at 978 MHz is also the exclusive home of FIS-B information. But there are some drawbacks. The biggest issue is that UAT is currently supported only in the United States, meaning that any international flight requiring ADS-B is off the table. Another potential issue is that you have to maintain your existing Mode C transponder. If you need to add a new Mode C transponder for some reason, the UAT option may be less economical than the 1090 option.
So let’s talk about 1090 “extended squitter” (1090ES), which is an enhancement of the Mode S transponder. Mode S transponders already squit, but 1090ES sends more information. In case you are wondering about the somewhat funny word, “squit” is essentially the opposite of a squawk, meaning that it sends information automatically rather than waiting for a radar interrogation. The information from 1090ES is identical to that which UAT sends, but it goes at 1090 MHz rather than 978 MHz.
The Garmin GTX-330ES is an example of a 1090 MHz Extended Squitter. Photo courtesy of Garmin
In addition to being the accepted international standard and being required above 18,000 feet MSL in the United States, 1090ES also replaces your existing transponder. This means that one box will meet both the ADS-B and transponder requirement. The major drawback with 1090ES, aside from cost, is that a 1090ES ADS-B In system doesn’t receive FIS-B. We’ll talk about some fixes for that later. But other than cost and FIS-B compatibility, 1090ES makes a strong case for better operational flexibility, simplicity, and potentially even resale value.
I Challenge you to a Dual
With some customers torn between the pros and cons of each ADS-B Out option, manufacturers created an interesting solution. Enter the dual band receiver. From a technical perspective, this is the “ideal” solution. The dual band units generally have a 1090 ES transponder integrated with an ADS-B-In system that receives both 1090 MHz and 978 MHz. This choice gives the pilot the operational advantages of 1090ES Out, but with the benefit of 978 MHz ADS-B In, namely FIS-B. Another benefit is having ADS-B In on both 1090/978 MHz, which means that your aircraft can receive traffic information directly from both bands. A single band receiver, whether 1090 or 978, only receives traffic information from aircraft on the same band directly from the aircraft. Full traffic information would still be provided, but it would depend on having the information rebroadcast from FAA ground stations. This isn’t a huge benefit, but it’s something to keep in mind if you fly outside FAA ground station coverage on a regular basis. 1090ES Out transponders also meet Mode C/S requirements anywhere in the world.
Embracing a Split Strategy
While a dual band receiver might be the “technically ideal” solution, it might not be the most financially appealing one. In that case, you might opt to adopt what I’ll call a split strategy. The FAA is only requiring ADS-B Out. To meet the legal requirement, you can install an ADS-B Out system, 1090ES or UAT. These systems are generally cheaper than a dual band or single band Out/In system. Installing ADS-B Out meets the mandate but doesn’t get you FIS-B or any traffic information. To handle ADS-B In, there are a number of portable systems that allow you to add ADS-B In to your other cockpit devices like tablets or portable GPS systems. Many of these systems are even dual band receivers. While they don’t integrate into your avionics and are generally limited to displaying on portable devices, they do provide a low cost, no installation option to pilots who want to add ADS-B In to an ADS-B Out only installation. You can also add this option later on if you desire.
The Avidyne AXP-322 is a remote mounted 1090 MHz Extended Squitter that can be controlled through other cockpit systems like the pictured IFD 550. Photo courtesy of Avidyne
Finding the Best Path
The clock is running and, as we have stressed, the FAA is not going to stop the clock or add extra time. The market has responded, and ADS-B options are plentiful. They range widely in price and capability from units that meet the standard and nothing more, to those with a host of features beyond the basics.
Since price and capability are not always highly correlated, a bit of research is in order.
A good place to start is the FAA’s Equip ADS-B page: www.faa.gov/nextgen/equipadsb. You can search and see what options are available for your particular aircraft, and that may help narrow your choices. Next, look for an avionics shop with experience installing ADS-B equipment. They can provide options and estimated costs. They can also tell you which options are most popular given your aircraft and needs. This is a great way to benefit from the experience of thousands of pilots who have traveled down this path before you. You are best positioned to find your best path, but it doesn’t have to be a solitary struggle.
Content disclaimer: Products and services mentioned, and/or external, non-FAA links within, do not constitute official endorsement on behalf of the FAA.
James Williams is FAA Safety Briefing’s associate editor and photo editor. He is also a pilot and ground instructor.
This article was originally published in the January/February 2019 issue of FAA Safety Briefing magazine.