ADS-B for General Aviation

Merger with adsbforgeneralaviation.com

2011-12-01T15:14:00.001-05:00

A while ago I was contacted by Glen Maxson; he's a retired Information Technology engineer from Intel who has started a website specifically about ADS-B and how it's introduction will affect GA. As a private pilot and technology expert in infrastructure, security, information and technology lifecycle matters, he has a good background to provide leadership on this topic. Most of all, he's really passionate about safety in the skies and the benefits we'll realize from ADS-B in this regard. His website is intended to be a place where holistic information about ADS-B can be found. Some examples would be:

- Current news about ADS-B

- Avionics Reviews
- Installation Experiences
- What do aircraft owners need to know before they buy an ADS-B unit?
- What's working and what's not

- And other topics of interest to the GA community with respect to ADS-B

His website can be found here: http://adsbforgeneralaviation.com/

Glen and I have decided to combine our efforts. Glen will continue to be the editor of his website and from time to time I will contribute with articles and the like as topics of interest come up. As a result, this blog will not be continued. I want to thank all of you who have visited and subscribed to this blog with your comments, thoughts and support. It's been instructional to me and hope that you were able to benefit from the content that was provided.

Regards,

Fabrice

Two MIT Conference Papers on ADS-B

2011-09-30T11:33:00.002-04:00

This past week, AIAA organized the Aviation Technology, Integration and Operations (ATIO) Conference in Virginia Beach. We participated with two papers that discussed some of the results of our work:

1. Mid-Air Collision Risk and Areas of High Benefit for Collision Alerting
This first paper was motivated by our new research direction of using ADS-B to provide reliable traffic alerting to all of GA. In order to understand where an aviator is most likely to be involved in a mid-air collision and thus a traffic alerting system would have to be operational, we conducted a survey of the mid-air collisions as well as near mid-air collisions of the past 10 years. The paper outlines the results and can be found here.

2. Survey of Potential ADS-B Benefits for the Soaring Community
The second paper was a survey of 272 soaring pilots. The survey was conducted in order to determine where the soaring community would perceive benefits from ADS-B. The paper outlines the survey results and can be found here.

ADS-B Traffic Alerting as Future Direction of Research

2011-08-12T15:00:00.004-04:00

As described in my Masters Thesis, ADS-B Traffic Alerting has been identified as a high value ADS-B application from the perspective of GA. In response to that, recent work here at MIT has focused on taking the required steps to make it a reality. In fact, the mid-air collision analysis presented in my thesis served as a basis to identify where such a system would have the most benefit. It was very clear: 59% of mid-air collisions happen in the vicinity of an airport with over half of them occurring between aircraft going in generally the same direction (see figure).

This is interesting -- if we are to create a Traffic Alerting System that is of benefit to GA, it needs to be capable of operating in the airport vicinity as well as the traffic pattern between aircraft that have small relative velocities. Current systems such as TCAS are not very good at doing that reliably.

In order to develop such a system, research into how to best alert in an airport environment will be required. This is the focus of our current work - development of new algorithms, evaluating Human Factors aspects such as display symboligy and heads down time, flight testing, etc. which will keep us busy through 2013.

Some of the work that has happened over the summer has resulted in a few papers that will be published at ATIO this September. I will post the links to them once they are published.

Masters Thesis on ADS-B Benefits to General Aviation

2011-06-02T17:41:00.003-04:00

Over the last two months I have been working on my Masters Thesis. In it, I take a look at the overall ADS-B system, it's benefits to GA and what the possible barriers are to the delivery of those benefits. In a sense, it takes some of the arguments given in previous posts a level deeper and gives more in depth information about some of the technical aspects of ADS-B.

The final version can be found here.

Installation of ADS-B Avionics: STC Required

2011-03-02T14:45:00.004-05:00

If you were to purchase an ADS-B unit today, you would not be able to install it in your airplane unless you get a Supplemental Type Certificate (STC) for the installation (FAA Memo). As would be expected, this memo was met with much outcry - and rightfully so. If the only way to install ADS-B is via an STC, cost to equip a GA aircraft would increase by as much as 700 percent, the Aircraft Electronics Association (AEA) said. This would create a dis-incentive to equipping with ADS-B and stifle acceptance of ADS-B within GA.

I believe those reactions are justified - nonetheless, I think they are based on a limited understanding of what the FAA intends to do or of the issues that influenced this policy. I believe that there may be a hidden benefit in this approach that I have not seen mentioned in any of the articles and that would make this a very smart move if executed correctly.

Here's a little background: The final ADS-B Out rule requires ADS-B installations to comply with technical standard DO-260B. Back in the 90s and early 2000s when ADS-B first came onto the scene, aircraft were equipped according to the then current version of this standard, DO-260 (no B). Since then, the FAA and industry have identified serious flaws with this first version - namely, some of the parameters it requires to be transmitted in the ADS-B message were interpreted differently by the various avionics manufacturers.
This resulted in a lack of consistency across the broadcast messages and there are now thousands of aircraft transmitting ADS-B messages that are misinterpreted by the ADS-B receivers on the ground.
For example, one aircraft may be on approach to JFK while according to it's ADS-B message it is over Russia somewhere (good thing we have radar). Additional issues specific to the GPS units used for those installations have also been identified.

This technical standard has since been updated twice to address these issues and is currently DO-260B. As you can imagine, not knowing whether you can trust an ADS-B message or not has massive implications for the utility of the entire system - as such, ensuring that ADS-B installations are truly in accordance with the specifications for the system is of utmost importance.

The FAA requiring an STC for the first generation of ADS-B avionics and their installations will help to prevent such problems. Since the industry is not used to manufacturing and installing ADS-B avionics, and the STC option seems very reasonable "to ensure consistent performance", as stated in the memo. In the long run, it will ensure that the ADS-B messages transmitted by all aircraft can be trusted by ground stations for surveillance as well as by other aircraft for ADS-B In applications, ensuring the delivery of the promised benefit.

Now, I agree that this policy of STC-only installations cannot remain in effect indefinitely. In fact the FAA agrees with that. In the memo requiring the STC's it states:

"It is expected that as both the FAA and industry gain experience on these initial installations, that the FAA will allow other approvals, including field approvals."

So, as long as this policy is not extended for too long, it may actually benefit all operators, including GA.

(The memo also identifies the Advisory Circular that outlines how ADS-B avionics are to be installed (AC 20-165). I recommend reading it - it helped me understand the capabilities of ADS-B and it's potential for revolutionizing the way we do aircraft surveillance and operations.)

ADS-B and Controller/Pilot Workload

2011-02-04T11:59:00.004-05:00

First of all, I want to apologize for the delay in writing posts - I had to pass my PhD qualification exams at the end of January and that kind of consumed all my time for the last month…

Last month I received a good question from Dan:

How do you think ADS-B would change the amount of coordination between GA pilots and controllers? Take flight following procedures and utilization, if pilots can see the traffic picture in the cockpit, would they even need flight following?

This question is a point of discussion on a few levels within the FAA. Generally it is expected that pilot/controller communication will go down which would result in a reduction in workload. However, it is unclear to me whether the workload will truly go down or if it will just change in nature:

Factors speaking for a reduction in pilot/controller workload

As pilots have better information available in the cockpit, they will have to rely less and less on ATC to provide them with that information. This can manifest itself in two ways:

First, as a result of the ADS-B data-link (FIS-B and TIS-B), requests for NAS status information from ATC (e.g. weather briefings from Flight Service) would decrease, resulting in a reduction in radio transmissions.
Second, as more and more ADS-B applications come online (Traffic Alerting, In-Trail Procedures, etc.), in essence we'll see a transfer of responsibility from the controller to the pilot. This transfer may be implicit (pilot monitors traffic display in cockpit instead of solely relying on call-outs from ATC) or explicit where ATC may instruct a pilot to follow another aircraft at a given interval. In an explicit transfer, the pilot is responsible for a certain aspect of ATC (e.g. separation from a specific aircraft) as opposed to the controller, therefore reducing the controller's work load.

Factors speaking for a change in nature of workload

The argument here is that workload would not necessarily go down but change from active control to much more of a supervisory control workload. Instead of instructing aircraft what to do, ATC would shift to increasingly monitoring compliance with given instructions (such as the keeping of an interval or separation).
Also, new vocabulary as well as procedures would have to be introduced for these new ADS-B applications. One example that is currently being debated is how to refer to a third-party aircraft during an ATC clearance. If aircraft A is instructed to follow aircraft B, how does ATC refer to Aircraft B so that Aircraft B doesn't mistake the instruction as a clearance for itself.

There is another element which I did not mention above which is that there will an increase in overall surveillance quality as well as total surveillance coverage volume. As such, ATC will be able to better advise pilots of nearby traffic, minimum safe altitude warnings (MSAW), etc. Also, from a search and rescue perspective, the last know position will be more accurate and potentially be lower to the ground than what is currently available with radar.
These benefits would lead to a potential increase in ATC workload because more pilots would now wish to utilize flight following.

In my opinion, there will be a net decrease in the number of radio transmissions as a result of ADS-B but I don't believe that workload will necessarily be reduced accordingly.

Please feel free to leave a comment below if you see other elements that would affect pilot/controller communications and workload!

Number of GA Aircraft vs. Number of GA Hours Flown

2010-12-20T12:00:00.002-05:00

One discussion that keeps coming up is how ADS-B will truly provide value to GA -- after all, GA pilots (and aircraft) only fly infrequently compared to commercial aircraft that can get around 5 flight legs per day. I'll try to shed some light on this in this post.

As discussed in the Equipage is crucial post, GA makes up for 95% of all the active aircraft in the NAS today. However, if we re-plot this graph based on yearly hours flown per aircraft, the picture does in fact change.

In 2008, the average GA aircraft flew 113 hours per year where the average commercial aircraft flew 2406 hours per year. Taking these numbers, it appears that if benefit from ADS-B is mainly accrued based on how many hours an aircraft flies, GA would truly need to have a much higher "per hour benefit" than commercial aviation would require.

There is another way to look at the same question, though. Keeping in mind that the active aircraft fleet in the US consists of 95% GA aircraft, summing the total flight hours in the National airspace system shows the following trend:

Currenlty, GA flies 57% of all the hours flown in the national airspace system -- that means that GA contributes more flight hours to the NAS than commercial aviation does. I found that to be a rather surprising result.

This brings us back to the benefit question. Benefits that increase efficiency in the NAS (such as more direct routing due to ADS-B) are more directly tied to how many hours are flown and mostly bring benefit to the aircraft getting the improved efficiency. As such, "increased efficiency benefits" will mostly help commercial aviation and it would be difficult for GA to make a cost benefit case, soely based on efficiency benefits. However, as the above plot shows, it is a different story if we look at the overall system.
There is another category of benefits that is more subtle but I believe much more important for GA: Situational Awareness. Situational Awareness includes having better knowledge of the traffic in the area, the weather in the area, the status of the airports of interest, etc. This type of benefit is not necessarily tied to how many hours are flown but are an overall improvement over the current status quo -- especially for GA (commercial aviation already have those systems). Since GA as a whole flies more hours than commercial aviation, this type of benefit would favor GA rather than commercial aviation.
As you can see, the way benefits are delivered from ADS-B differs from GA to commercial aviation. As a result, the benefit case is much more difficult and not as straight forward -- it's difficult to put a dollar value on improved Situation Awareness and the resulting Safety Improvements.

TSO'd vs. non-TSO'd ADS-B Avioncis: NavWorx

2010-11-18T08:49:00.006-05:00

Since October 31st, NavWorx has been shipping their ADS600's; avionics that receive TIS-B and FIS-B and, if you get the ADS600-B, even transmits ADS-B Out. Priced at $2500, these units may seem to be an attractive solution for an early ADS-B adopter. However, there are two issues:

1. The NavWorx unit is not TSO'd. This means that you will not be compliant with the final ADS-B rule and will have to buy another set of ADS-B avionics (or an update) once the final mandate comes around. This will place you right in the price range of other units that are scheduled to be released next year (2011), fully certified.

2. Just getting an ADS-B In unit (like the ADS600) will not enable you to receive TIS-B. TIS-B is only broadcast if there is an aircraft present that is actually transmitting ADS-B Out. Here's a quote from the company deploying the ADS-B infrastructure (ITT):

"In order to considered a TIS-B client, an aircraft must be [transmitting] ADS-B-OUT, must have produced valid position data within the last 30s to an [ADS-B] ground station, [and] must be under surveillance of at least one secondary radar (...)"

As you can see, you need to really be a player in the system - just showing up with a receiver might not work so well. You could get lucky - if there is an aircraft that is transmitting in the area, he'll "turn on" the system and you'll of course receive the same data he does.

Update (12/11/2010): As a reader correctly noted, TIS-B is client based, FIS-B is not. In fact, FIS-B is broadcast all the time. The post has been modified accordingly.

Update 2 (2/7/2011): Multiple readers have noted that NavWorx is planning on getting a TSO for their unit and possibly offering free upgrades. I have yet to get confirmation on this but that would certainly make this unit an attractive way to become rule compliant.

Update 3: (2/9/2011): I received an email from the President of NavWorx last night. Here are a couple of important excerpts:

1. "Later this year, we will offer a certified GPS internal to our ADS600-B, as well as a stand-alone certified GPS too. Estimated pricing for the "bundled" ADS600-B with internal certified GPS is $3999.00"

2. "When we achieve (expected) certification later this year, we will trade any of our non-certified units for the certified units; the customer merely has to pay for shipping and if they don’t trade in within 3 months of the certification date, they may incur any inflationary price increases that we would have to pass on."

He seemed to be confused by one thing I wrote above: It's not the GPS that determines whether or not TIS-B gets broadcast - it's whether or not someone "turns on" the TIS-B broadcast by sending ADS-B Out messages. The post has been edited for clarity.

Bundeled ADS-B Avionics

2010-11-05T09:27:00.001-04:00

An interesting development ever since the rule was published was the emerging of bundled ADS-B avionics. If you remember from the ADS-B Architecture post, a complete ADS-B system consists of a position source (GPS), ADS-B Receiver/Transceiver, a set of antennas and the altimeter. Not mentioned in that post, it also needs to get your squawk code from your transponder.

Apparently to reduce cost, some manufacturers have now started to bundle some of these components:

FreeFlight Systems:
FreeFlight is developing avionics that combine the GPS and the ADS-B component. The system is one box remotely mounted in the aircraft with a control head in the cockpit. Currently projected cost (without installation) is:

GPS/ADS-B Out: $6,295
GPS/ADS-B IN: $6,995

Until development is complete, it is unclear whether or not the GPS can also be used for navigation; however, in a conversation an engineer mentioned that it should be possible.

Sandia Aerospace:
Sandia bundles their avionics differently. Its unit scheduled for release in early 2011 and combines ADS-B IN and OUT with a standard Mode C transponder. The projected cost without installation is $3,500.

One great aspect about this unit is that it has the dimensions of your standard transponder and it is intended to be a drop in replacement for your transponder greatly reducing installation cost.

I believe that this is a very encouraging development. Seeing prices for an ADS-B unit combined with a GPS lower than what a GPS used to be by itself is a strong indication that competition in the market is working in favor of General Aviation pilots by reducing the final cost to equip.
However, some of the manufacturers are still somewhat hesitant about developing ADS-B avionics. Some believe that they cannot trust in that the FAA's final rule is truly final while others simply believe that 2020 is too far away to really start investing the capital now. I'm hoping that as these fears wane, we will yet see prices fall again.

Nationwide Roll-Out of ADS-B

2010-10-20T12:47:00.003-04:00

Two weeks ago, the FAA gave ITT the "go-ahead" to install ADS-B nationwide. In FAA lingo this is called the In-Service Decision (ISD).
Up to this point, the FAA had been evaluating the system in a few keysites; each keysite specific to evaluating specific elements of the system.
According to Vinny Capezzuto - the FAA's ADS-B Program Manager - this roll out will result in 50% of the radars to be decommissioned over the next decade while around 800 ADS-B radios will be erected across the country.

Having received the ISD, ATC is now allowed to use ADS-B for separating aircraft -- controllers will be shown a fused image of traffic symbols displaying ADS-B targets as well as radar targets on the same screen.
Nationwide coverage from ADS-B is expected by 2013 and, according to Vinny Capezzuto, the program is very well on track and indications are that it will actually be done by then.

Comprehensive ADS-B Article by Aviation Week

2010-10-20T12:28:00.005-04:00

Fred George of Aviation Week recently published a well written article reviewing the final ADS-B out rule. I recommend you read it but for those of you short on time, here are a couple of highlights:

"(...) If you could pick a model program, ADS-B is it. The FAA adopted almost every single recommendation. We got everything we asked for in the final rule," said Pete Bunce, president of GAMA.

From a general aviation standpoint this is a very true statement - the FAA has been bending over backwards to accommodate GA in this endeavor.

In the final rule, the FAA also eased off on the navigation sensor position and velocity accuracy requirements contained in the NPRM. This virtually eliminates the requirement for WAAS or other satellite-based augmentation systems as the sole navigation sensor capable of meeting the navigational accuracy specs. However, standard TSO-C129 GPS sensors will have to be modified or replaced to meet TSO-C196, a new standard with tougher operating software requirements and aircraft-based GPS augmentation.

I'm not so sure about this - I'm reviewing TSO-C196 to see if avionics under it could be used for ADS-B position information. Right now I don't think so but if the claim were true we would see some nice cost savings on the GPS side of the avionics architecture.

Update: After going through TSO-C196 it seems like there might be an additional pathway to get ADS-B rule complinat navigation infromation besides the WAAS GPS approach (TSO-C145c). I have not seen a manufacturer that currently offers TSO-129a upgrades but potentially this could keep many users from having to purchase a new WAAS GPS.

"This is the 'final rule' for today, but I doubt it's the final, final ADS-B rule," said Bill Stone, Garmin's avionics products manager.

That overtone concerns operators. As many as 150,000 aircraft will have to be fitted with ADS-B Out equipment. Operators are not anxious to upgrade avionics for ADS-B Out in the near future, only to face a separate mandate for ADS-B In at a later date.

There is only partial truth to that. There will probably be things we find out as we go but for now, the FAA has made it very clear that the rule will not change. In a conversation with a senior FAA official that was responsible for the rule, he answered this same question with a very firm "No. Out of question."

Operators won't realize most of the benefits of ADS-B without ADS-B In as well as ADS-B Out. ADS-B In makes possible airport surface situational awareness functions, in-trail self-spacing procedures, interval management, ASSA and FAROA, according to the final rule.

Similarly, general aviation aircraft will need compatible CDTI screens to support ADS-B In. Most current-generation MFDs and GPS navigation boxes with large-screen moving maps may be upgradable for CDTI functionality.

More than three-quarters of the U.S. general aviation fleet now uses GPS for navigation. But only a small portion of these units are WAAS boxes that meet the ADS-B Out accuracy and integrity requirements.

ADS-B Upgrades to Mode S Transponders

2010-10-19T13:25:00.002-04:00

Mode S transponders can be upgraded to comply with 1090ES ADS-B regulations. It is somewhat less clear on which transponders can be upgraded and who can do it; so make sure you contact your avionics technician about you specific model.

Garmin and TRIG have announced that they will have upgrades to their existing transponders available, but only Garmin is showing number right now:

Garmin GTX328/330: $1200 (Garmin Quote, 2009)

There is a GTX330D which has antenna diversity; to get full benefit from ADS-B In, antenna diversity is a must. To upgrade at GTX330 to 330D, Garmin quoted $6500 in 2009.

There are a few new 1090ES ADS-B/Mode S Transponders being brought to the market, too, such as the ones from Dynon.

An interesting recommendation that I was given was to not upgrade any Mode S transponder. The individual suggested to just keep using the transponder as is and once 2020 comes around buy a 1090ES Transponder with ADS-B capability. The cost difference would be minimal since by then 1090ES ADS-B would have come down in price to be comparable to today's upgrade cost.

Cost Reduction from GPS WAAS Upgrades

2010-10-16T15:16:00.004-04:00

As hinted before, there is a potential for substantial savings on the overall cost for an ADS-B system. Namely, it is to upgrade an existing GPS tor be WAAS compliant.

Having WAAS GPS instead of non-augmented GPS means that your navigation equipment is now certified under a different TSO. Instead of TSO-C129 which is for non-WAAS GPS, WAAS GPS is certified under TSO-C145 or C146, depending if the unit is stand-alone or integrated with other avionics. As a result, you can now use your GPS for more than just "supplemental navigation" as you would be allowed to under C129. Also, of course, you can now use it for ADS-B.

Looking at the GPS systems that are currently most widely used in General Aviation (namely Garmin and Honeywell's Bendix/King), we find the following upgrade paths:

Garmin 400/500 series factory upgrade: $3000
Bendix King: Has hinted at an upgrade path for the KLN94 but an upgrade is currently questionable.
Antenna Replacement/Installation: ~$1500

Total Cost for WAAS Upgrade (Garmin 400/500-series): $4500

For a good discussion on this topic, check out this article. The next post will look at transponder upgrades.

Cost for new 1090ES ADS-B Out Avioncis

2010-10-04T09:13:00.002-04:00

To install an all new 1090ES ADS-B Out suite, you need a Mode ES Transponder (similar to a Mode S transponder) as well as a WAAS enabled GPS. Here are the prices for new equipment:

Mode ES Transponder: $2,200 (not installed, GTX330)
WAAS GPS: $8,500 (installed, E.g. G400)
Installation Cost: $1,500 (estimated)

Total Cost for new 1090ES ADS-B Avionics Installation: $12,200

As can be seen, 1090ES is about as expensive as UAT. It's difficult to compare just the two prices, however. The UAT installation only has one antenna where the Mode S Transponder generally comes with an antenna diversity capability. Though this doesn't have to be installed, you still get the functionality and therefore more value for your money.
From a safety perspective, dual antennas are a must (gives you visibility of/to everybody flying above you) where the decision to go to UAT gives you a potential benefit from FIS-B (weather data in the cockpit) if you were to equip with ADS-B IN down the road. As you can see, the cost is similar for both set-ups but the capabilities you receive are not the same. Which one is right for you will depend on your specific flying habits.

Now that we have the basic cost/understanding for what it takes to be rule compliant, we can get into some of the more interesting avionics and capability comparisons. We'll be looking at upgrade paths (instead of buying new like described here), as well as the bundling of components - one of the most recent developments in ADS-B avionics.

Cost for new UAT ADS-B Out Avioncis

2010-09-28T13:23:00.003-04:00

Finally the work of the past few weeks is producing some fruit. This first post will look at the equipment (and its cost, of course) required to achieve ADS-B Out capability as required by the FAA ADS-B Out rule. For now, I will focus solely on new ADS-B equipment - upgrades to already existing equipment will be covered in a separate post.

Tangent: It turns out that figuring out how much it costs to become ADS-B Out rule compliant is not as simple as it sounds. Given all the different equipment currently on the market, I ended up getting hundreds of different combinations between avionics types, manufacturers and certification standards. In fact, there was such a wealth of information that I will add a specific page on this blog that will list all the available avionics, their prices and how the can be upgraded, how the interact with others, etc. Here I will only present an approximate cost for each component.

On to the important stuff: As mentioned before, a UAT ADS-B Out installation needs three components: a WAAS enabled GPS, a UAT Transponder and an Antenna Diplexer.

To buy new equipment, the prices for 2010 are as follows:

GPS Unit: $8,500 (e.g. G400W, panel mount, installed)
UAT ADS-B Transponder: $3,000 (e.g. FreeFlight Systems RANGR Transmitter, includes $1000 for installation)
Antenna Diplexer: $1000 (FAA Quote, installed)

Total Cost for UAT ADS-B Out Installation: $12,500

There are two caveats with this number. First, comparing this number to a similar cost analysis I did last year, the price has reduced by 50%. The main driver on this is the dropped requirement for Antenna Diversity and the publication of the final rule. After the publication, multiple manufacturers announced the development of these units resulting in increased competition.
Second, some manufacturers have announced the development of integrated avioncis (i. e. GPS bundled with ADS-B transmitter). Those units are expected to decrease the cost even further.

Great Article on WAAS GPS for ADS-B

2010-09-08T16:41:00.005-04:00

I just read a great article by the Avionics Magazine (part of Aviation Today). In great detail, the writer talks about the background of WAAS and how it fits into the greater picture of GPS Navigation.
As described in the Equipage Level post, a WAAS enabled GPS is one of the position sources that can be used to comply with the requirements of the ADS-B out rule.

A couple of highlights from the article:

- A good description of the three different classes of Beta WAAS receivers
- A quick overview of the standard that governs TSO-C145c
- Overview of recent market developments
- A list of TSO-C145 GPS manufacturers

The list of the manufacturers will come in handy in the cost analysis that has been previously mentioned and that is currently in the works.

A question for you: What kind of GPS do you have on the aircraft you most often fly (make/model)?

ADS-B Avionics Architecture: 1090ES and UAT

2010-08-30T14:02:00.005-04:00

To understand how much it will cost for GA operators to equip with ADS-B Out avionics, it is crucial to understand the setup of ADS-B avionics. Since there are two different links in the United States, there are two possible ways and aircraft can be modified to comply with the ADS-B Out rule.

UAT ADS-B Out Avionics Architecture:

The figure below shows the components that are required to set up ADS-B on board an aircraft. The small number in the corner of the boxes is the percentage of aircraft that are currently equipped with that functionality (according to the FAA 2007 Avionics survey, see previous post).

1090ES ADS-B Out Avionics Architecture:

The figure below shows the setup required to comply with the ADS-B Out rule using 1090ES.

As can be seen, the 1090ES architecture requires less components. This is mainly because the transponder also performs the ADS-B Out function, removing the requirement for a stand alone ADS-B unit. This will ultimately have a large effect in overall cost -- upgrading a transponder (if possible) is less expensive than buying a new, standalone ADS-B unit. The next post will analyze the specific costs that are expected to achieve this avionics setup.

Current Level of GA Equipage with Avionics required for ADS-B

2010-08-19T15:35:00.003-04:00

Under the final ADS-B Out rule, aircraft are required to have the following equipment onboard the aircraft:

1. Navigation (or Position) Source

This component is what determines the position as well as velocity of the aircraft that is then broadcast via the ADS-B message. Contrary to what many pilots think, this doesn’t have to be a GPS. The final rule only states the parameters that have to be satisfied by this equipment; for example the horizontal position accuracy has to be less than 0.05NM and the velocity accuracy has to be less than 10 meters per second. As long as the position source meets these and requirements in the rule, it can be used as for ADS-B.
However, from a General Aviation perspective, this position source will most likely be a GPS. Also, the only stand-alone (that is, non-coupled) navigation equipment today that can satisfy the requirements in the rule is a WAAS enabled GPS in accordance with any revision of TSO-C146.
Current Percentage of TSO-C146 GPS in GA Fleet: 17.86%*

Update: As Henry Billingsley from Free Flight System correctly noted, any revision of TSO-C146 can be used to comply with this requirement. This post has been corrected accordingly. Appendix 2 of Advisory Circular AC-20-165 has more details.

2. ADS-B Avionics

Using the position information from the navigation source, altitude from the altimeter and other hard coded information, this component creates the actual ADS-B message.
For UAT ADS-B avionics, this would be a stand-alone box where for 1090ES ADS-B this function would be performed by the transponder.
As stated in the final rule, this component needs to satisfy TSO-154c (UAT) or TSO-166b (1090ES).
Current Percentage of TSO-154c ADS-B Avionics in GA Fleet: 0%* Current Percentage of TSO-154c ADS-B Avionics in GA Fleet: 0%*

2. Transponder

Though many suggested removing the requirement for a transponder after ADS-B is mandated, the final rule did not adopt that suggestion. One of the reasons the FAA does not want to remove transponders right away is that without them, in case of a GPS or ADS-B outage, ATC would not be able to control traffic were it not for secondary radar.
For ADS-B, you’ll either continue using your existing Mode A/C Transponder alongside with a standalone ADS-B unit, or, you upgrade an existing Mode S Transponder to 1090ES ADS-B.

Current Percentage of Mode A/C Transponder Equipage in GA Fleet: 83.67% Current Percentage of Mode S Transponder Equipage in GA Fleet: 10.51%

3. Antenna: ADS-B and Transponder

ADS-B signals need to be transmitted via an antenna. The proposed rule suggested that everybody install two antennas: one at the top of the aircraft to be used for ADS-B In communications with other aircraft above you as well as one antenna on the belly of the aircraft for transmissions to the ground/other aircraft below you.
(Having these two antennas is called antenna diversity).
After much pushback by the industry, the final rule now only requires ADS-B to be transmitted from a single antenna at the bottom of the aircraft.
To further minimize the cost of an ADS-B installation, the FAA included a technical specification in the UAT ADS-B standard that allows sharing of a single antenna between the transponder and the ADS-B unit. This device is called an antenna diplexer.
Bottom Line: If you have a transponder, you will not have to install a new antenna. All you’ll need is an antenna diplexer.
However, having only a bottom antenna will reduce your visibility to/of other aircraft that fly above you which may result in reduced benefit as some of the proposed ADS-B applications will not work as well without Antenna Diversity.
Current Percentage of Antenna Diplexer Equipage in GA Fleet: 0% Current Percentage of Antenna Diversity Equipage in GA Fleet: 10.51%**

5. Altitude Encoding Altimeter

Lastly, the final rule states that the altitude information transmitted in the ADS-B message has to come from the same source as the altitude transmitted by the transponder. This indirectly results in a requirement for some kind of altitude encoding altimeter.

Current Percentage of Altitude Encoding Altimeter Equipage in GA Fleet: 87.29%***

Note: All percentages are based on the 2007 FAA Avionics survey. In it, some operators reported ADS-B equipment. This equipment is what is called “Legacy ADS-B Equipment” and it is not in accordance with the final rule. It may be possible to upgrade this equipment to the respective TSO’s.

*Standard was published after 2007, I could not find any manufacturers that currently manufacture equipment to this standard (in Aug 2010).
** Based on Mode S Transponder equipage – Mode S usually has antenna diversity.
*** Based on Mode C and Mode S Transponder equipage.

Analyzing Cost to Equip with ADS-B

2010-08-12T14:48:00.001-04:00

As stated in Resolving the Cost/Benefit Case post, Benefit and Cost for a new technology have to be balanced to achieve wide acceptance. If it costs more than what you get from it, people will not want to buy it. So, in our first excursion, we have looked at what applications provide the most benefit to General Aviation (see previous post). Now, the next step is to find out what the cost is to achieve this benefit.

The cost, of course, is directly tied to the new avionics that need to be installed on the aircraft. This is where things get somewhat complicated: First, not every aircraft has the same equipment currently installed. Some might have nothing but the minimum required by FAR 91.205 (TOMATO FLAMES and FLAPS) where others have the latest glass cockpit with an integrated collision avoidance system.
On top of the different types of currently installed equipment, there are two different options to upgrade to ADS-B: 1090ES or UAT.
As a result, many different combinations that would all cost a different amount – some might be able to retrofit existing equipment where others would have to buy brand new equipment.

So here are the next steps:
1. Gain an understanding of the current levels of equipage of General Aviation Aircraft
2. Understand the Avionics architecture required to operate with 1090ES ADS-B
3. Understand the Avionics architecture required to operate with UAT ADS-B
4. Calculate cost for different upgrade paths to comply with the ADS-B out rule

For the first step, we will use the FAA’s 2008 General Aviation Survey that can be found here.
For step 2 and 3, we will use the ADS-B out Final Rule that was published in May 2010; it can be found here.
Lastly, for step four we will be using market values of common avionics and their installation cost.

High User Benefit Applications for General Aviation

2010-07-30T09:44:00.005-04:00

The process described by the Mapping Application Benefit to GA User Groups post resulted in the following list of high value applications (see here for descriptions of the applications). The applications listed had a weighted average of greater than 2.5:

ADS-B Out Applications:
ATC Surveillance in Non-Radar Airspace
ADS-B Enhance Flight Following
Improved Search and Rescue
ELT Application
FBO/Online/Company Flight Tracking

ADS-B In Applications:
Enhanced Visual Acquisition of Traffic
Airborne Conflict Management (ATSA-AIRB)
Cockpit Display based, VFR like separation in all weather conditions
ADS-B based Situation Awareness on the Airport Surface (ATSA-SURF)
Obstacle Awareness Application

Data Link Applications:
TIS-B
FIS-B

As can be seen, these applications are mostly focused on enhancing flight safety as opposed to increasing efficiency (which is one major thing the airlines expect to receive from ADS-B).

Disclaimer: This list of applications is not meant to be the end all be all. It is more-so a starting point and gives direction for future research. Namely, from a GA perspective, it appears that research should be mostly directed toward implementing applications enhancing flight safety.

What do you think? Do you agree with this list? Would you add/replace applications? Let me know by leaving a comment!

Mapping Application Benefit to GA User Groups

2010-07-29T16:23:00.009-04:00

In the Increasing Benefit for GA post, 42 ADS-B applications were identified. Understanding which of those applications are most beneficial for GA will inform what applications that should be implemented first -- resulting in benefit from ADS-B being delivered sooner. A list like that could be used by the FAA to identify what procedures have to be developed, what flight test need to be conducted, etc.

There is a complication that arises when trying to do this: General Aviation is very diverse - it ranges from the occasional recreational pilot to the commercial pilot flying jets for a company. As such, the type of operation these two pilots conduct are substantially different and therefore the applications they would prefer would also differ. At the same time, there are probably more recreational pilots than there are jet pilots in GA and so they would carry more weight.

Therefore, to get a selection of applications that represents General Aviation as a whole, the following process was used:

1. Identify the major subgroups within General Aviation
Four user groups were identified within GA: Recreational Flying, Business Flying, Flight Training and Aerial Application/Other which contained Agricultural operation, EMS, etc. These categories are based on the FAA's 2007 General Aviation Survey.

2. Assign Weighting Factor to Each Subgroup
This evaluation was also based on the FAA's GA survey. Of all the hours flown in 2007, they were distributed as follows:

Recreational Flying: 37.10%
Business Flying: 26.48%
Flight Training: 15.97%
Aerial App./Other: 20.45%

3. Evaluate Benefit of a Given Application to Each Subgroup
This was the most difficult part. Using the literature mentioned in the previous post, an overall benefit assessment was conducted and each application ranked for each subgroup. The scale used was 1 for low benefit, 2 for medium benefit and 3 for high benefit.

4. Create a Weighted Average Benefit Value
Multiplying the weighing factor with the benefit for each of the subgroups gives an overall Benefit ranking for each application

I know this is somewhat confusing -- so here is an example:

Once each application was evaluated, a list of the applications with the highest scores could be created.

Increasing Beneift from ADS-B to General Aviation

2010-07-02T11:31:00.006-04:00

The first step is to understand how ADS-B delivers Benefit to General Aviation. As can be seen in the previous post, ADS-B applications are the primary means by which ADS-B delivers benefit to the pilot. (That is not to say that there are no other, second order effects of ADS-B that are beneficial.)

So the initial step was to do a literature review as comprehensive as possible to get an accurate understanding of the ADS-B applications that have been proposed to this day. Long story short, 191 applications were identified, of which 42 were unique. A list of them along with a description can be found here.
As can be seen, two categories emerge: ADS-B Out applications and ADS-B In applications. In essence, this goes back to the equipage of the aircraft: If an aircraft is only equipped with ADS-B Out, the only applications it can perform/partake in are the ones listed in the ADS-B Out category. The same goes for the ADS-B In applications.

Now that we have a list of applications, the next step is to identify what applications deliver most benefit to GA. More on this in the next post.

Resolving the ADS-B Cost/Benefit Case for GA

2010-07-01T16:21:00.005-04:00

The FAA published the final ADS-B Out rule on May 28th, 2010. One of the headings reads: General Aviation: High Equipage Cost with Little Benefit. This problem has been apparent for quite some time and the response of the General Aviation community to the publication of the rule was correspondingly negative. The reason my research was funded ago was to address this problem.
The research approach taken is a simple cost/benefit approach: To resolve this dilemma, either the Benefit has to be increased to make ADS-B worth the cost, or the cost has to be reduced to match the benefit (or both).
In other words: How can the Benefit from ADS-B for GA be increased and what can be done to reduce the cost of ADS-B to GA. The first step is to understand how ADS-B delivers Benefit to GA:

Once benefit delivery mechanism are understood, the cost to GA needs to be analyzed:

Each of these steps will be addressed individually.

System Components 3/3: Operating Procedures and definition of an "ADS-B Application"

2010-06-03T16:24:00.007-04:00

Operating Procedures, the last of the three components, govern the interaction between the ground infrastructure and the airborne avionics as well as any interactions between aircraft that use ADS-B. Just as today there are procedures that are being used to dictate how pilots and controllers interact using radar, ADS-B requires a set of procedures that dictate how controllers and pilots use ADS-B. A majority of ADS-B procedures are related to "ADS-B Applications".

An ADS-B application is a functionality in the National Airspace System that is enabled by ADS-B.

ADS-B applications are what ultimately deliver the benefit from ADS-B. It is those applications that allow us to harvest the advantages ADS-B technology offers over radar. Below is a list of a three proposed ADS-B applications:

ATC Surveillance in Non-Radar Airspace (ADS-B NRA)
ADS-B based Airborne Conflict Management
Improved Search and Rescue

System Components 2/3: Aircraft Equipage (Airborne Component)

2010-06-03T15:56:00.004-04:00

The equipment needed to comply with the ADS-B requirement will be what creates most of the cost for the individual aircraft owner. At a conceptual level, the following components are required in addition to what is currently required by the Federal Aviation Regulations (FARs):

High-End Navigation Unit: This can be a GPS or any other accurate enough device. The requirements dictate that the reported position that is transmitted via ADS-B needs to be very accurate; thus, this navigation unit needs to be of high quality (more on this in a later post).

ADS-B Transmitter: This component is what actually crates the ADS-B message. It receives the information from the navigation unit as well as the altimeter. (An altitude encoding altimeter would be required of course; however, most aircraft already have one.)

Antenna Diversity: Fancy for "a top and a bottom antenna". The addition of a second antenna increases the number of aircraft that receive the ADS-B message directly, increasing the efficiency of the system. Some of the currently existing transponder antennas might be usable to satisfy this requirement.

UPDATE: The final rule was recently issued; Antenna Diversity is no longer a requirement.

Conceptually, these are the three major components of the ADS-B avionics. In real life, it is a little more complicated mostly because of the two different link architectures and the possibility of upgrading existing equipment to comply. Later posts will address these difficulties.

System Components 1/3: ADS-B Ground Infrastructure, TIS-B, FIS-B and ADS-R

2010-06-03T14:53:00.014-04:00

The ground infrastructure consists mostly of the antenna ground stations (also called radios) that receive the ADS-B messages, and the equipment used to integrate those messages into the existing Air Traffic Control (ATC) system. There are a total of about 1000 ground stations proposed across the US which are supposed to be installed by 2010. The figure below shows such a ground station (found here):

Each tower has four directional 1090 MHz antennas (for 1090ES ADS-B) and one unidirectional UAT antenna. In addition to the ADS-B antennas, there are sometimes other antennas present such as AWOS or shielding antennas.

The messages picked up by the antennas are routed via private networks to three control stations in Ashburn, VA, Dallas and Phoenix. There they are validated, fused with existing radar data and then forwarded to the ATC system where they are ultimately used for surveillance. From receiving to delivery of the message, no more than .7 seconds are allowed to pass.

One of the challenges in the system is that surveillance data from two source has to be merged; namely radar surveillance data and of course ADS-B surveillance data. For example, it has to ensure that there are no duplicate reports that could unnecessarily set of a collision warning in an ATC facility (for more information, see the AviationWeek article in the March 8th, 2010 issue).

Another purpose of the ground station is to broadcast TIS-B, FIS-B and ADS-R which can be received by aircraft via ADS-B IN:

TIS-B (Traffic Information Service - Broadcast) transmits traffic data that was gathered using radar; in other words, it transmits the traffic targets that cannot be "seen" by ADS-B. This information is used to supplement the traffic situation displayed on the CDTI (top figure below).

FIS-B (Flight Information Service - Broadcast) contains information relevant to the pilot such as weather, national airspace status, NOTAM's, etc. It is only available on UAT.

ADS-R (Automatic Dependent Surveillance - Rebroadcast) rebroadcasts messages received on UAT in 1090ES and vice versa. This is also used to supplement traffic on the CDTI.

The physical implementation of ADS-B: Three Main System Components

2010-06-03T11:25:00.009-04:00

The overall ADS-B system can be broken down into three different subcomponents:

Ground Infrastructure
Airborne Component
Operating Procedures

These three components are needed to enable ADS-B in the National Air Space system. If any one of these components is not available or functioning properly, the overall ADS-B system would operate in a less than-optimal-state, if at all.

Another way to state this is to say that these three components as well as their interactions must be optimized as to maximize the benefit that results from their usage and the ADS-B system as a whole.

The figure below depicts this well (adapted from this paper by Mozdzanowska et al.):

The three components on the left enable applications of ADS-B which ultimately brings different benefits (b1 - b3) to the users and stakeholders (represented by stk 1-3). At the same time, the components need to be made, installed, etc. and that is associated with a cost (c1 - c3).

The distribution of cost and benefit in this image are not optimal. User 3 carries most of the cost while getting least of the benefit. Of course, such cases need to be avoided because they would create a disincentive for users to equip (see the Equipage is Crucial post).

In the next posts, each of the tree components will be addressed individually.

ADS-B in the US: 1090ES and UAT

2010-03-25T13:47:00.008-04:00

After the FAA committed to implementing NextGen and with it ADS-B in the US, initial stakeholder reviews suggested that ADS-B would provide insufficient benefit for General Aviation. As stated in the Aircraft Equipage is Crucial for ADS-B Beneift post, not having General Aviation equip could be very bad for the ADS-B system.

To create an incentive for General Aviation, the FAA decided to provide a free link to weather information in cockpit (FIS-B) via ADS-B In.
There was only one problem: The initially proposed ADS-B frequency (1090 MHz) has insufficient bandwidth to carry this amount of data in addition to all the transponder replies, TCAS interrogations, etc.
As a result, the FAA decided to implement a Dual Link Strategy. It keeps the 1090ES ADS-B available in the US but adds UAT ADS-B (Universal Access Transceiver) for General Aviation on 978 MHz.

However, since the US is the only country to implement UAT, any aircraft with UAT ADS-B avionics would have to follow special procedures to leave the US since it would not comply with the international 1090ES ADS-B standard.

This has serious implications about the ADS-B system design. An aircraft equipped with 1090ES ADS-B can now not receive UAT ADS-B messages since the frequencies are different. Also, the ground infrastructure has to be capable to of receiving ADS-B messages on two different frequencies.

The FAA plans to deal with this using ADS-R. ADS-R translates all the UAT ADS-B messages into 1090ES messages (and vice-versa) and periodically send them out.

ADS-B Internationally: 1090ES ADS-B

2010-03-25T13:19:00.006-04:00

The radio frequency that is used for ADS-B internationally is 1090 MHz. This frequency is the same as what is used by aircraft transponders to reply to interrogations from ground radars.

ADS-B emerged out of this currently used transponder technology. Most general aviation aircraft have a Mode C transponder. A Mode C transponder replies to radar interrogations on 1090MHz with an altitude as well as a transponder code that is set by the pilot.
A more advanced type of transponder is the Mode S transponder. It also provides a transponder code and altitude information but is essentially a data package protocol that allows for individual Mode S transponders and radars to communicate with each other directly.

ADS-B was then another upgrade to this Mode S technology. The existing Mode S transponder message is enhanced to contain all the information needed for the ADS-B message such as position, velocity, etc. This is known as 1090ES ADS-B.

As a result, since Mode S Transponders on 1090 MHz are already internationally used and regulated, the international standard for ADS-B will be 1090ES ADS-B.

Aircraft Equipage is Crucial for ADS-B Benefit

2010-03-25T12:56:00.007-04:00

ADS-B has a very unique characteristic: Unless other aircraft are equipped, your aircraft's ADS-B unit will not help you much. In other words, the benefits to a specific operator are co-dependent on the level of equipage of all other aircraft. The more aircraft that participate in ADS-B, the more beneficial the ADS-B system becomes.

As a result, the FAA is very interested in fostering a high percentage of equipage as soon as possible. Initially, the research that we are doing here at MIT was born out of this desire to create incentives for operators to equip.

After an initial review of the current fleet of aircraft in the US, it became apparent that General Aviation has been largely left out in the design of NextGen. And, since GA makes up 96% of the aircraft fleet in the US (see below), the efficiency of the ADS-B system would be diminished if General Aviation would not willingly equip with ADS-B.

To avoid this, the FAA has started to address how ADS-B could bring benefit to GA. Our research here at MIT are intended to help with this potential problem.

NextGen and SESAR

2010-03-25T12:39:00.003-04:00

As stated in the "Why move the ADS-B?" entry, many major Air Transportation Systems are closing in on a major capacity problem. In the US and Europe, the aviation authorities have proposed NextGen and SESAR, respectively, to deal with the challenges of their aging Airspace System.
ADS-B is one of the major enabling technologies for this change. Besides ADS-B, RNP (satellite based navigation) as well as vastly improved system wide information management are two of the other fundamental improvements.

Why move to ADS-B?

2010-03-25T11:46:00.006-04:00

A question that I get asked sometimes is "The radar system we have is working pretty well; why are we switching to ADS-B?"
The main reason is that the current Airspace System is reaching its capacity limit. To quote Professor Hansman at MIT, a leading expert in this matter: "The US, European and other Key Air Transportation Systems are approaching a critical saturation threshold where nominal interruptions (e.g. weather) result in a nonlinear amplification of delay." [1]
In the US, one reason for this problem is that the basic architecture of the Airspace System dates back to the 1950 when the FAA was first established. Back then, pilots mostly navigated by outside references such as fires on the ground or landmarks. The radar system was put in place to try to pin-point the aircraft position from the ground to avoid collisions in the air. The accuracy of those radars back then resulted in the creation of the 5-mile en-route (3-mile for terminal areas) separation standard.

Though radars have become much more accurate over the past fifty years, separation standards have not been changed (i.e. reduced). Also, air traffic in the US has increased substantially during that time period, ultimately contributing to the congestion that Prof. Hansman is talking about.

Besides the improvement of the radars, aircraft have become much "smarter". Today, most aircraft have on-board navigation system that can pin-point the aircraft's location more accurately than a radar on the ground could.

ADS-B takes advantage of exactly that fact: Instead of looking at the sky using radars to locate aircraft, the aircraft transmits it's position to the ground. This signals a fundamental change in surveillance: It's a move from ground based surveillance to satellite based surveillance. This results in many advantages:

Higher update rate than radar ADS-B transmits every second instead of 12 (en-route radar) or 4.8 (terminal radar) seconds.

Higher Velocity Accuracy Radar uses an algorithm to determine the velocity from consecutive hits and can take up to 30 seconds to actually get an estimate. ADS-B transmits the velocity directly from navigation source every second.

Potentially higher position accuracy As distance increase from the radar dish, the radar beam width also increases resulting in decreased accuracy with growing distance from the radar. ADS-B transmits position as determined by the navigation source; the accuracy remains the same no matter how far away from the receiver.

ADS-B provides heading information Just like the velocity, radar derives the heading from multiple radar hits. ADS-B transmits the actual heading as determined by the navigation source.

ADS-B messages can contain intent information ADS-B can be used to tell the controller on the ground (or other aircraft) a future path.

ADS-B allows for more even task distribution Pilots in appropriately equipped aircraft can see the same traffic image that he controller sees on his screen. This allows for some of the separation responsibility to be transferred to the pilot.

ADS-B is a data-link Data such as weather and traffic information (FIS-B, TIS-B, etc) can be transmitted directly to the cockpit.

Ground infrastructure is cheaper An ADS-B antenna is one order of magnitude cheaper than a radar installation.

[1] Lecture in "The Airline Industry" at MIT in 2008

ADS-B Worldwide

2010-03-25T11:08:00.005-04:00

The United States is neither the first nor the only country that is moving to ADS-B as their future means of air traffic surveillance. In Australia, the first ADS-B antennae were turned on in 2006. For Australia, ADS-B was an easy decision; radars were only installed along the coast resulting in vast stretches of un-surveyed land in-between the coasts. ADS-B presented a cost effective way to provides surveillance in those areas.

The figure above shows what countries are evaluating, planning or implementing ADS-B.

Survey: ADS-B for Soaring Pilots

2010-03-23T12:28:00.005-04:00

In light of recent mid-air collisions involving gliders, MIT in collaboration with the FAA and the MITRE Corporation has started a project evaluating how ADS-B could be of benefit to the Soaring Community. The survey can be found here:

http://agena.mit.edu/ADSBsurvey

The soaring community is of special interest. Since they are non-electric aircraft (i.e. most of them do not have an electrical system), they are exempt from the FAA's transponder rule. As a result, they cannot be detected by ATC's secondary radar system (SSR).
The project mentioned above focuses on creating a low-cost, battery operated ADS-B system that could be installed in gliders; this would result in greatly increased situation awareness on the pilots as well as the Air Traffic Controllers part.
Preliminary flight tests are planned for this summer (2010). The survey was created to ensure that these flight tests actually evaluate issues of interest to the soaring community.

Previous MIT work on ADS-B related to GA

2010-03-23T12:08:00.007-04:00

In 2007, Edward (Ted) Lester wrote his Master's Thesis on the topic "Benefits and Incentives for ADS-B Equipage in the National Airspace System". In his thesis he presents the results of a survey of the US pilot population and their take on ADS-B and its benefits to General Aviation. The thesis can be found here.

His general conclusion was that ADS-B has great promise but that there are multiple "potential stumbling blocks (...): industry opposition, lack of FAA infrastructure implementation, and surpassing technologies."

ADS-B Explained

2010-03-15T21:06:00.002-04:00

As depicted by the blue lines in the figure below, ADS-B is a service where aircraft broadcast their altitude, heading, speed, GPS-determined position as well as other information. This broadcast data is known as ADS-B Out.

Ground stations (transceivers) will receive the ADS-B Out message and display it on the Air Traffic Controller's screen. Because these ground stations are less expensive than the existing radar installations, they can be installed in more locations giving controllers radar-like coverage and control in non-radar environments. Also, since ADS-B messages are sent out once per second (as opposed to 12 seconds for en-route radar), there is a much higher update rate providing the controller with more timely data.

ADS-B Out messages can also be picked up by other aircraft in the vicinity. This capability of receiving ADS-B messages on-board the aircraft is known as ADS-B In (depicted by the green arrows in the figure below).

ADS-B In messages that originated from other aircraft can be used to display traffic in the vicinity to the pilot using a cockpit display (see figure below, top).

ADS-B In messages can also originate from the ground stations and be used to transmit data (such as weather information) directly to the cockpit. The received ADS-B In messages can then be displayed to the pilot on a Cockpit Display of Traffic Information (CDTI) as shown in the Figure below (bottom).

ADS-B for General Aviation

2010-03-15T20:44:00.001-04:00

In an effort to modernize the National Airspace System, the FAA recently began the process of implementing of Automatic Dependent Surveillance-Broadcast (ADS-B) in the US. ADS-B will be the basis of the future surveillance system in the US.
Here at the MIT Department of Aeronautics and Astronautics we are trying to understand how ADS-B could benefit General Aviation in the US. This blog is a place where the results of this research will be posted.