Time Is Running Out For Your Comments!

by ANN Guest Contributor Max Trescott

There’s always a marriage of sorts between pilots and Air Traffic Control, and final vows are about to be exchanged for the FAA’s NextGen Notice of Proposed Rulemaking (NPRM). The proposal mandates ADS-B equipment in all aircraft by 2020, but the deadline for comments is just two weeks away, so now is the time for you to carefully read this prenuptial agreement.

In the past, the FAA has embarked on other multi-billion dollar modernization programs that ballooned in size and failed to deliver as promised. This program could be more successful than those, but it may need changes to optimize it to deliver the right benefits at the lowest cost. Whether you own or rent, your money is at stake and you have until March 3, 2008 to submit comments to the FAA.

To date, the industry has been relatively quiet on the proposal. That’s surprising since, by FAA estimates, GA aircraft owners can expect to pay from $4,000 to $17,000 to bring each aircraft into compliance by 2020. However, if owners think that complying with the mandate will bring free traffic and weather information into the cockpit, they haven’t been paying attention, because it won’t. The full text of the NPRM, which runs 25 pages, can be downloaded as a pfd file. 

The underlying premise is that demand for air travel will double over the next 20 years, but that the present US Air Traffic Control system (ATC) is not designed to handle this growth. One constraint is the use of radar technology. Radar is sufficiently inaccurate at longer distances that ATC must keep the moving dots separated by five miles in order to assure that the real airplanes—which may not be exactly where the dots indicate they are—don’t collide with each other. Radar is also expensive to maintain, since it requires large, rotating antennas sited on leased land.

The goals of NextGen include improving safety and efficiency by taking advantage of emerging technologies, namely ADS-B. ADS-B uses GPS receivers on board each aircraft to identify aircraft position more precisely than is possible using radar. It broadcasts this position information so that other ADS-B equipped aircraft, surface vehicles and ground stations are aware of the aircraft’s position. ADS-B has been successfully demonstrated for several years in Alaska as part of the Capstone project. Accidents decreased by 45%, though much of this decline may be attributable to "ADS-B In" capability, not the "ADS-B Out" capability mandated in this NPRM. Here’s the difference.

ADS-B stands for Automatic Dependent Surveillance-Broadcast. It is Automatic because unlike a transponder, it broadcasts continuously, not just when interrogated by radar or a TCAS system. It is Dependent, since it relies on GPS information. It provides the same Surveillance function as radar, but does so by Broadcasting its position.

There are two ADS-B capabilities. "ADS-B Out," which is the only one mandated in the NPRM, refers to an aircraft broadcasting its position and other information. "ADS-B In," which is not being mandated, allows an aircraft to receive traffic information from other ADS-B equipped aircraft, surface vehicles, and FAA ground stations. Weather and other information can be delivered to aircraft additionally equipped with Flight Information Services-Broadcast or FIS-B.

If you’re thinking "wait a minute, I’m spending big bucks for ADS-B Out, but I won’t get any additional information displayed in my aircraft," you’re absolutely right, though the option to receive information is available to you at additional cost. In a sense, ADS-B is a transponder replacement, except that you won’t be allowed to eliminate the transponder, which is needed as a back-up to ADS-B—more on that in a moment. First, let’s talk about benefits.

Proposed NextGen Benefits

A major proposed benefit is that the more accurate data from ADS-B will allow the five mile en route separation between aircraft to be reduced, allowing more aircraft to fit into the NAS. Yet as one commenter to the proposal stated, "reducing enroute and/or terminal separation standards WILL NOT address the congestion problem.  Traffic congestion is caused by lack of runway, taxiway, and ramp/gate capacity due to airline ‘hub & spoke’ scheduling practices."  You can view this and all comments to the NPRM online.

Another proposed benefit is that the FAA can save money by eliminating some radar installations. However, some of this potential savings is negated by the need to have a backup plan in case the ADS-B system fails. This would be needed if, for example, there were a wide spread outage of GPS service. The proposed backup plan is to retain all primary radar, which is still needed for national defense to identify non-participating aircraft, and to retain approximately half of the secondary radar installations near the nation’s largest airports. Hence, the mode C transponder requirement remains in place so that aircraft will be visible to secondary radar, when needed for backup.

Clearly, the costs and benefits are asymmetrical. The FAA may save money by eliminating some radar installations, but that’s offset by the requirement for pilots to spend thousands of dollars to equip each aircraft with ADS-B. Recognizing this, the NPRM does solicit comments on how to subsidize the costs to pilots and some state legislatures are considering this. On the benefits side, the FAA may succeed in squeezing more aircraft into the en route structure, but pilots who opt for the minimum required ADS-B Out requirement derive little benefit, except for continued access to the NAS.

ADS-B Regulatory Requirements

ADS-B wouldn’t be required everywhere; the requirements are similar to that of mode C transponders. To review, mode C transponders are required when operating above 10,000 feet MSL, within 30 miles of some, mostly Class B airports, and when flying under, above or through Class B and C airspace. There is an exclusion related to flying within 30 miles of Class B airports for "any aircraft which was not originally certificated with an engine-driven electrical system" and the ADS-B proposal includes the same exclusion. Mode C transponders are not required above 10,000 feet if one remains within 2,500 feet of the ground, however the ADS-B proposal does not include that exclusion.

The ADS-B proposal further mandates that aircraft operating in Class E airspace over the Gulf of Mexico, from the coastline out to 12 NM and above 3,000 feet MSL, would require ADS-B Out. This area, which contains hundreds of helicopters servicing thousands of offshore oil wells, doesn’t have radar coverage, so ADS-B would enhance surveillance in this area.

A seemingly odd requirement is that aircraft flying above FL240 will use a different ADS-B system, known as 1090ES, than many lower flying aircraft. Presumably, this is to rationalize the U.S. ADS-B proposal with that of existing 1090ES standards in some other countries. Thus, high flying aircraft traveling between continents could have the same standard ADS-B system, regardless of where they fly.

The rub is that this equipment has a lower bandwidth and cannot accommodate FIS-B capabilities, such as the display of weather in the cockpit. Thus, another ADS-B unit, called a Universal Access Transceiver (UAT) and operated on a different frequency, is proposed as an alternate way for lower flying aircraft, that are presumably more interested in these services, to comply with the ADS-B mandate. This complicates implementation of the proposal, as aircraft using these two different types of ADS-B equipment won’t be able to directly communicate and "see" each other. Hence, the proposal includes many ADS-R translators, which are sets of crosslinked, ground-based transceivers that re-broadcast all ADS-B signals on both frequencies. This should allow all ADS-B equipped aircraft, regardless of the standard they use, to see each other—except when they are not within line of sight of a ground-based ADS-R site.

Proposal Comments

Reading through the comments, many of them well thought out, is enlightening. Here are a few. The NTSB wonders why the proposal doesn’t mandate ADS-B In, which could provide additional safety information to pilots that would prevent incidents such as runway incursions. An individual points out that in many cases, the cost to install ADS-B represents one tenth to one third of the total value of older aircraft. A few people commented on security issues, including the lack of data encryption that might allow ADS-B to be used as a tool for terrorists to target aircraft.

Several comments focused on the requirement for ADS-R to handle the two different ADS-B standards. One said "The added risk of faults, failures, and ‘aged data’ (latency) in the additional computer hardware and software to accommodate two separate links (not to mention the additional infrastructure cost) makes the proposed implementation ludicrous."

Another individual, commenting on the illusory benefits of equipping with just the minimum required ADS-B Out, said "It's totally unclear what benefits, if any, will accrue to users if they equip with only the proposed ADS-B Out option."

Get Involved: Send Your Comments Today

While ADS-B holds tremendous promise, the current proposal represents a compromise that could be improved upon. Clearly the FAA has chosen to reduce pilot cost by not mandating ADS-B In, even though there’s little benefit to pilots of equipping with just ADS-B Out. Many of the services, such as weather, that would make ADS-B In valuable require equipment that differs from the ADS-B standard, used in some other countries. Thus two different standards were proposed, which increase the cost of the ground infrastructure and decrease overall system performance. However, since the time when ADS-B was first developed, some of these services, such as weather, have become available separately from third party providers. Meanwhile, the ADS-B freight train is hurtling down the tracks, as the contract has already been let for installing the ground infrastructure.

Any time billions are being spent—both of taxpayer money and of aircraft owners’ money—it pays to take a close look. Final comments on the proposal are due March 3, 2008, so read the proposal carefully. Then send your comments to AOPA, or click here to enter them yourself online. Just as in a wedding ceremony, you need to "Speak now or forever hold your peace."

Max Trescott (shown above) is an experienced CFI, author, and aviation educator.

FMI: www.maxtrescott.com, www.adsb.gov, Send Your Comments Here!