ADS-B: Answering your ADS-B questions

ADS-B uses GPS satellites instead of ground-based radar to determine aircraft location and is a key technology behind the FAA’s Next Generation Air Transportation System. ADS-B In—which provides the ability to display weather, notams, and other data on cockpit displays or wirelessly on a tablet—is optional.

Today’s frequently asked questions are those asked most recently of the technicians in AOPA’s Pilot Information Center, who field hundreds of ADS-B-related phone calls and emails each month.

ADS-B Technology

What type of airspace will require ADS-B Out? If aircraft owners are still asking, we must not have said it enough:

• Class A, B, and C airspace.
• Mode C veil around Class B primary airports.
• Above the ceiling and within the lateral boundaries of Class B or Class C.
• Class E airspace at and above 10,000 feet msl over the continental United States, exclu-ding airspace at and below 2,500 feet agl.
• Class E airspace over the Gulf of Mexico at and above 3,000 feet msl within 12 nm of the U.S. coast.

Except for the Gulf of Mexico, ADS-B airspace—defined in FAR 91.225—is the same airspace where an attitude-encoding transponder is required today.

Can ADS-B at some point replace the need for a transponder? Probably. However, for the foreseeable future, transponders will be required for traffic alert and collision avoidance system (TCAS) compatibility, cross-border operations, and to transit most TFRs.

What is the best ADS-B system for my aircraft? Because ADS-B can touch so many systems aboard an aircraft, there’s no one-size-fits-all solution—and no way to answer without knowing more about the aircraft and how it’s used. But you’ll find good information in “ADS-B: Questions to Ask” (November 2016 AOPA Pilot) and “ADS-B: Case Studies” (July 2018 AOPA Pilot).

Can I fly outside the United States with 978UAT only? It depends. If the country has not implemented an ADS-B Out mandate, you can fly there with 978UAT. However, you must comply with any mandates, and 1090-MHz Extended Squitter (1090ES) is the only international standard; today 978UAT is supported only in the United States.

When will Canada require ADS-B out? We don’t yet know, but Canada is working toward an ADS-B Out mandate, and we do expect that it will be for the 1090ES international standard.

ADS-B Performance

My ADS-B performance report indicates my equipment failed. What do the flight test results mean? Anything highlighted in red on an FAA Public ADS-B Performance Report indicates a failure. The email accompanying your performance report includes a link to the FAA’s PAPR Users Guide, which also is available online. This is a comprehensive and helpful document.

If a parameter fails 100 percent of the time, it’s a hard failure most often resulting from a system configuration error when programming the unit at installation. A failure 1 or 2 percent of the time is more of a nuisance failure, and might be caused by brief masking of the GPS and/or ADS-B antenna during the flight.

The report looks at many aspects of the ADS-B Flight ID; common problems are omitting the “N” from the aircraft’s N-number—or conversely, entering only the N within the field. A partial failure also could be caused by flying at the edge of ADS-B ground station coverage.

If the emitter category is highlighted in red, make sure it’s configured properly. Most GA aircraft will be 1, “Light”—this is for aircraft weighing less than 15,500 pounds. (If your installer selected “Small” and your aircraft isn’t greater than or equal to 15,500 pounds and less than 75,000 pounds, it’s the wrong choice.)

Although the ADS-B final rule was published in May 2010, aircraft owners still have a lot of questions.NIC, NAC, and SIL are GPS parameters. Don’t panic if they’re all flagged as 100-percent failures; the cause is usually a simple (if not intuitive) configuration error. Early on, some Garmin installations were seeing failures here; the installer scrolled through a configuration menu until reaching “ADSB”—except the correct setting was the next one, “ADSB PLUS” (this mistake is uncommon today). A 100-percent failure could mean your ADS-B hardware or software is not compatible with your position source; more often it’s just improper system configuration. Partial failure can be caused by flight at the fringe of ADS-B ground station coverage, antenna masking caused by maneuvering, or intermittent loss of GPS service.

Under kinematics, the system makes a reasonableness check of changes in barometric and/or GPS altitude, position, and velocity. Anything highlighted in red indicates position changes outside the range expected for normal aircraft performance.

Air on ground means that the FAA ground system received messages indicating the aircraft was airborne while it was on the airport surface. This could indicate a squat switch issue, that the GPS stall speed setting is incorrect—too low a stall speed can cause the avionics to transition to air mode during high-speed taxi—or the avionics initializing in air mode at startup.

Many parameters report maximum consecutive failures, which is the number of consecutive noncomplying reports received. If an MCF exceeds its threshold, an MCF exception is flagged.

Here’s an important tip: If you fail the performance test while trying to qualify for the FAA’s $500 ADS-B rebate, email the rebate help address and ask for a review of your (failing) results. If they can tell you why you failed the first time, it will be much easier to prevent a recurrence.

FAA Rebate

Is the rebate retroactive for those who recently installed, but before the rebate program was re-launched? Unfortunately, no. We have been told that the FAA cannot consider rebates for aircraft that have flown with ADS-B Out in the National Airspace System before October 12, 2018.

Why didn’t AOPA fight to make this rebate retroactive for those of us who installed in the last year? AOPA’s government affairs team had been lobbying to bring back the rebate as a means to encourage additional ADS-B equipage, and asked about aircraft owners who had equipped since the initial rebate period. However, the government-approved rules for the rebate program did not allow retroactive rebates.

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