US Operators and ADS-B Out

[completely deck]

I was wondering if the current US airline operators (CO, WN, DL, XE, etc) have the capabilities to transmit ADS-B out on all of their aircraft already. If so, are they (the operators) waiting on the mandate in 2020 to become active before they use it on every flight (regardless of overseas ops or not)?

Reason I ask is that I do have an ADS-B receiver and while I see the aircraft that obviously need ADS-B (international overseas flights), I sometimes see sporadic flights that don't usually need ADS-B. For example, a CO flight from IAH-MCO (753) will show up, but not a XE flight from IAH-MCO. And a Citation flying domestically will show up, but not a WN flight. Is this purely because of ops, or do these aircraft not have the ability to transmit yet?

Thanks

[FlightPathOBN]

The ground based portion of ADSB is still being constructed in the US, currently I believe on Louisville and Philly have operational systems.

This was supposed to be everywhere by 2015, but I believe it has slowed quite a bit...

[ATCast]

The ADS-B signal depends on the transponder on board of the aircraft. Most new aircraft have an ADS-B capable transponder, and in most cases the ADS-B function will be active. This it not something that is decided on a flight by flight basis, it's basically off or on (you can't switch it from the flightdeck AFAIK, unless you switch the transponder to off).

ADS-B is not necessary for international overseas flights, but it is mandated in Australia, above certain flightlevels over Hudson Bay in Canada, and in few other areas in the world.

The US rule is mandating ADS-B in 2020, Europe will most likely mandate ADS-B for new aircraft from 2015, combined with mandate to retrofit ADS-B from the end of 2017. However the rulemaking is not yet passed by the European Commision so these dates might change, although I think that's unlikely.

Assuming you have a SBS-1 station or something similar, note that not all aircraft that you see are sending the correct position. Some aircraft send their IRS position, which can be several kilometers off. This is indicated in the ADS-B position message by an integrity flag set to 0, but unfortunately the ADS-B stations that are commonly used for hobby purposes don't show this information.
Under the mandates (Australian, Canadian, European & US) the position source must be GPS (or a source with the equivalent or better accuracy & integrity, at the moment only GPS qualifies). In general an integrity number of 4 or 5 is needed for the ADS-B reports to qualify for ATC surveillance purposes.

Another thing is the ADS-B protocol version: Europe & the US will mandate version 2, while the aircraft that are equiped now use version 0 or 1.

Best,

ATCast

[FlightPathOBN]

I certainly hope your IRS position is not several kilometers off from actual! :rolleyes:

[ATCast]

I certainly hope your IRS position is not several kilometers off from actual!

Well I hoped that too, but reality proved me wrong. Look through a day of data on a site like casperflights and see how often a B733 or F70 lands next to a runway according to their ADS-B data. These aircraft typically have no GPS receiver connected to the transponder and send out IRS data instead. Sometimes they are far off.

Departing aircraft sometimes seem to have the wrong runway set (e.g. L instead of R, or opposite threshold) when they start their takeoff roll, although this happens not so frequently.

[FlightPathOBN]

ahhh..I see, I was thinking the 37's NG, which have a GPS updated IRU...

[Denti]

Actually, it doesn't. Both GPS and IRS positions are fed into the FMC which then uses both (and radio update) to compute its position, but the IRS is not directly updated by the GPS.

[FlightPathOBN]

Honeywell Inertial Ref system is standard on many Airbus and Boeing models...

"Three Air Data Inertial Reference Units (ADIRUs) each comprise three ring laser gyros and three quartz accelerometers to accurately sense aircraft position and attitude. By integrating data from the inertial sensors and Global Positioning System (GPS), ADIRS provides automatic initialization, faster align times and 100 percent availability of Required Navigation Performance approaches."

Air Data Inertial Reference Unit - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Air_Data_Inertial_Reference_Unit)

[HEATHROW DIRECTOR]

Using SBS, there is nothing uncommon in seeing aircraft "land" several miles away from Heathrow. Similar inaccuracies can be seen from visual observations.

I hope they sort it before it is ever used for ATC purposes.

[FlightPathOBN]

Concur, the lack of a standard protocol is a significant issue for EuroControl/FAA right now. There are a whole bunch of people without operational experience working on the signal protocol, and terminology is right out the window....
(stuck right now with airspace floor/ceiling unions and exclusions) :ugh:

[Denti]

Wikipedia is often not a good source of information, especially to the more arcarne stuff.

Boeing 737 RNP approaches do not need any GPS actually, boeing got an FAA (and EASA) approval to fly any RNP approach including GPS approaches as long as the FMC computed ANP is sufficient, no GPS updating is needed for RNP 0.3, it is however needed for less than 0.3. The FCOM says about the IRS outputs: IRS outputs are independent of external navigation aids. GPS is such an external navigation aid.

Over a longer flight you can actually see how the IRS position (select POSition on the EFIS mode control panel) very very slowly moves away from radio and GPS positions. Oh, and there is of course no automatic initialization, you still have to supply the current position to align the IRS, same as in the old classic 737s.

[FlightPathOBN]

I only posted the wiki as a reference, the information came from Honeywell....

Honeywell's Inertial Navigation System Becomes Standard Equipment On Airbus (http://www51.honeywell.com/honeywell/news-events/press-releases-details/04.30.10ADIRS.html)

including GPS approaches as long as the FMC computed ANP is sufficient,

this is true, as long as your ANP growth hasnt exceeded 2xRNP...oops sorry thats .5nm

[FlightPathOBN]

Denti,

I dug into this a bit, as ANP growth is always a consideration in RNP design.
The INS/IRU is expected to be less than 2nm per 15 minutes. The FTE cannot exceed 1nm for enroute, 0.5 nm for approach transition and missed, and 0.25 nm for a non-precision approach, so one can work backwards to the update timing.

So I guess what you are saying is correct, the RNP approach is good without the GPS update, under some circumstances.

For procedure design, the limiting factor usually being the 0.5nm for the missed, and this is per criteria, not operational use....

[completely deck]

ADS-B is not necessary for international overseas flights, but it is mandated in Australia, above certain flightlevels over Hudson Bay in Canada, and in few other areas in the world.

You're absolutely right. I live near Houston so I confused that rule with the Gulf of Mexico rule. Flights over the Gulf are required to have ADS-B.

Most new aircraft have an ADS-B capable transponder, and in most cases the ADS-B function will be active. This it not something that is decided on a flight by flight basis, it's basically off or on (you can't switch it from the flightdeck AFAIK, unless you switch the transponder to off).

This may be true, but I'm curious to why if they have the equipment, why only transmit your altitude and nothing else such as lat/long, spd, callsign.

And yes, I have a miniADSB

[ATCast]

why only transmit your altitude and nothing else such as lat/long, spd, callsign.

What kind of aircraft do you see sending only altitude? I assume those are helicopters or light aircraft that don't have other information than altitude available to the transponder. In such case the transponder sends out altitude only on ADS-B (and maybe a few additional status messages).

Flights over the Gulf are required to have ADS-B.
The ADS-B-OUT rule (http://www.regulations.gov/#%21documentDetail;D=FAA-2007-29305-0289) for the US (include class E airspace over Gulf of Mexico) was accepted on May 27, 2010 and effective since August 11, 2010 but the compliance date is January 1, 2020. Until then you can expect to see non-compliant aircraft.

[Dont Hang Up]

HEATHROW DIRECTOR

Using SBS, there is nothing uncommon in seeing aircraft "land" several miles away from Heathrow. Similar inaccuracies can be seen from visual observations.

I hope they sort it before it is ever used for ATC purposes.


To be fair, the aircraft that are reporting the gross errors are also invariably reporting "minimum integrity" for the data. In other words they send the data with a qualifier that says the accuracy is not guaranteed to anything better than 20NM!

However I take your point, the data integrity issue does need to be fully resolved before ADS-B is used for ATC and this is very much part of the thinking of the current European mandate for aircraft equippage.

It is now recognised on both sides of the Atlantic that Version 2 aircraft equppage is the minimum requirement for ADS-B to be used for ATC. And currently aircraft are still mainly equipped with Version 0 and a very few with Version 1.

The Australians, who have been very much the front runners in using ADS-B, have taken a different approach in that installations were approved on an aircraft-by-aircraft basis (the so called "white list"). However even they would acknowledge that this was difficult to manage and I think will be happy to abandon it with the coming of Version 2.

[Wazzoo]

FlightPathOBN

ahhh..I see, I was thinking the 37's NG, which have a GPS updated IRU...

Honeywell Inertial Ref system is standard on many Airbus and Boeing models...

"Three Air Data Inertial Reference Units (ADIRUs) each comprise three ring l@ser gyros and three quartz accelerometers to accurately sense aircraft position and attitude. By integrating data from the inertial sensors and Global Positioning System (GPS), ADIRS provides automatic initialization, faster align times and 100 percent availability of Required Navigation Performance approaches."

Air Data Inertial Reference Unit - Wikipedia, the free encyclopedia

I can't speak for the Airbus but like Denti says I don't believe the GPS does update the IRS position, at least not on the 737NG, it does however update the FMC position. I can only add to the anecdotal evidence in that while I've seen the FMC and GPS position to be pretty much on top of the a/c position, you often see the left and right IRS wandering off in different directions and on long flights easily 3-4nm off the FMC computed and GPS positions.

The reference above to GPS used with the ADIRS is only referring to the initialising and alignment where the GPS position is manually inputted into the IRS system for the initial alignment.

I'm struggling to find an explicite statement to that affect that the GPS doesn't update the IRS for the 737 but I'm likewise not able to find anything that aludes to the contrary which I would think there would be if that was the case. There is however quite a bit about the GPS, Radio and IRS independently updating the FMC.

Vol 2 refers to the IRS and GPS systems as being independent systems. It talks about the FMC position being derived from a mathematical combination of the positions determined by the IRS, GPS and navigation radios and being updated from those sources with the GPS having highest priority. Mr Buffler also talks about the bias changing from almost all GPS to a mixture of GPS, IRS and Radio if the GPS doesn't have good satellite geometry.

Using these as independent sources with the bias changing depending on the quality of the position data each is providing would seem to go against the idea that one source is updating the other leading to potentially bad GPS data throwing the IRS even further off with both lots of bad data now being fed to the FMC.

[completely deck]

What kind of aircraft do you see sending only altitude? I assume those are helicopters or light aircraft that don't have other information than altitude available to the transponder. In such case the transponder sends out altitude only on ADS-B (and maybe a few additional status messages).This is the decoded data I'm getting for the a/c sending only altitude. Not all of them are like this, but most are. They have to be jets at least for being at FL340 and sending a Vmax code


A6CFFC Extended-squitt. United States 33975ft * CA:L2-air
A6CFFC Short-air-sourv. United States AC:33975ft Vmax:300..600kts
A6CFFC Extended-squitt. United States 34000ft * CA:L2-air
A6CFFC All-call-reply United States CA:L2-air

[aveng]

I'm struggling to find an explicite statement to that affect that the GPS doesn't update the IRS for the 737 but I'm likewise not able to find anything that aludes to the contrary which I would think there would be if that was the case. There is however quite a bit about the GPS, Radio and IRS independently updating the FMC.

My course notes say -
Multi-mode receiver 1 (MMR 1) and MMR 2 have data buses
to the ADIRUs. The MMRs do not supply any data to the
ADIRUs. The data buses are for future use to send
global positioning system (GPS) information.

As far as I know the MMR (GPS) position still goes directly to the FMC on the737NG, A330 however, GPS position goes via the ADIRU's to the FMGEC's.

As to the accuracy of ADS-B, its is still linked to the RNP and as such the MEL for both systems inop reflects this.:ok:

[FlightPathOBN]

Too much equipment, too little time! Airbus variants that use the Honeywell ADIRU, the GPS updates the IRU directly, which is why that unit has such high accuracy values. How the Smiths box handles this, I am not aware.

With regards to a non-GPS RNP procedure, yes, that would be considered an ANP approach, and as long as the ANP value does not exceed the RNP value, than this is all good. The 777 has the express feature that on disco of the GPS, the box defers to ANP.