GPS users must plan for outages

[DDF]

GPS users must plan for outages
Satellite woes mean that plan B is a must



Firms that rely on the US Global Positioning System (GPS) should ensure that they have a fallback plan, as one of the UK's top navigation experts has warned that the system may prove unreliable.

Speaking at a Cambridge University conference in September, Norman Bonnor, a retired RAF Air Commodore and president of the Royal Institute of Navigation, said the GPS signal is more fragile than many users might suppose. "Too many people don't understand its foibles and vulnerabilities," he added.

GPS is widely used in systems ranging from car navigation to emergency services co-ordination; and for time-keep- ing in utilities, finance and telecoms sectors.

The system relies on a network of satellites, which cannot be repaired once launched and have a limited lifespan. Sixteen of the present 28 satellites were built to last seven and a half years, but are now between eight and 14 years old. Twenty-four satellites are required for full coverage.

Bonnor said launches of new satellites are "only just keeping up" with current losses of around two satellites per year. But the failures could accelerate due to the number of satellites that have used up their redundant hardware. "Many are on their last legs," he explained.

The first of eight modernised satellites, built to last 10 years, was due to launch yesterday after a series of delays. A European alternative to GPS, called Galileo, is not expected to be complete until 2010.

Lem Bingley, IT Week 27 Sep 2005

[Fargoo]

Well what a coincidence! Europes' own system is on its final hurdle and here we have a retired curly tash rubbishing to US system which has served us all proud.
I wouldn't read too much into it, replacing a satellite is expensive but it's not much a problem.
Don't throw away your Tom Tom yet mate :)

[reynoldsno1]

To be fair to Mr. Bonnor, ISTR he is a former President/Chairman of the Royal Institute of Navigation, and well-respected.

One could also argue that the GPS space segment has proved to be remarkably robust, and the Block III replacement programme may have an even longer life....

[TopBunk]

AFAIK GPS outages are predictable and are promulgated by AIS notams as likely to affect certain airfields between specific times on specific dates as a function of satellite coverage, maintenance downtime etc.

Not being able to rely on GPS and to have a backup plan sounds eminently sensible in aviation to me. After all we don't plan on all engines, generators, hyd systems, etc working on board nor on the wx being fine nor the CAT3 ILS being available when flight planning.

GPS availability (or lack thereof) is just another part of the planning process, imho.

The US still have the ability to put an uncertainty factor into the GPS accuracy in times of need anyway, wouldn't that render GPS approaches invalid/unusable.

He may have a curly 'tach, but is he actually saying anything new?

[ShyTorque]

Another reason why a backup might be needed. A couple of weeks ago a NOTAM was issued warning of GPS jamming trials taking place in Wales.

The jamming WAS succesful - we saw it first hand, the system can be rendered useless. Our FMS warned us that it was receiving NO satellites for quite some distance as we flew over Wales. Thankfully it also receives DMEs so the accuracy was still acceptable.

[Blacksheep]

Navigating with a secondary system is good practice and has been for centuries. There's not much effort involved in running a raw data cross check against an old fashioned paper map at regular intervals. How else can you be absolutely certain that your FMS is telling the truth?

[Riverboat]

Great to know that if my highly reliable GPS which has never failed me in years - or ever for that matter - is switched off by the Americans, or just plain fails, I can use an NDB to precisely fly through thunderstorms etc.

What a joke! The GPS has proved itself to be a real boon to navigation, and I am amazed eminent people, including CAA folk, keep on about how potentially unreliable it is. Surely all our aids are potentially unreliable, and none of us would hang our lives on one aid.

As for the US shutting it down, this is not likely to happen without notice, as there are thousands of aircraft in American airspace using GPS, nearly all as their primary aid, and the US wouldn't forget that.

As for the requirement to still have an ADF and DME fitted in UK airspace if one wishes to fly airways - why? GPS can deal with both far easier. OK, if one is going to make use of an NDB as an approach aid, that is fair enough, but there ain't so many of these around now. Could someone please tell the CAA?

[mavila02]

New GPS satellite ensures future of system
When a new GPS satellite was launched on Sunday, some AOPA members wondered what it means for general aviation. The answer: GPS navigation will be around for a long time to come.

The new satellite replaces an aging bird that's nearing the end of its useful life, ensuring that the GPS signal will continue to be available even as some older satellites are taken off line.

"The latest launch represents a firm commitment to satellite navigation and demonstrates that there will be plenty of assets in space to ensure that the GPS signal is always available," said Randy Kenagy, AOPA senior director of advanced technology. "That's especially important for general aviation as more GPS-based wide area augmentation system (WAAS) approaches are created." WAAS approaches allow for ILS-like minima without the expensive ground-based equipment.

There are already several "hot spare" satellites on orbit should a GPS signal fail, and GPS availability is not a concern at this time.

The Air Force expects to launch an average of three new GPS satellites each year to replace older equipment.

September 29, 2005

[411A]

Lets remember 11Sept01, when all aircraft were ordered to land inbound to the USA, yet then, or in the days that followed, the GPS signal was not degraded or switched off.
So much for the switch off nonsense.

Now, I have been using GPS as a prime navigation aid for oceanic/long range flights for a rather long time, and in my private airplane as well, for just as long, yet I can count on exactly three times when the GPS signal faded or was not available...and never during an approach to GPS minimums.

Most of the sour grapes about the US GPS system can be traced to the 'not invented here' syndrome.
Not surprised at this at all.
That the USA thought the idea up and implemented same must be very upsetting to some...on the outside.:}

[CBA_caption]

The amount of US waeponry requiring suitable GPS reception means the Americans are not going to let the system fall out of the sky. Worst case is the degradation signal is switched back on requiring crypto for precision approaches. It'll still get you over the atlantic though. Your Garmin is safe.

CBA

[reynoldsno1]

As for the US shutting it down, this is not likely to happen without notice, as there are thousands of aircraft in American airspace using GPS, nearly all as their primary aid, and the US wouldn't forget that.

It hould also be remembered that the aviation segment makes up a relatively small percentage of GPS users. Land users are the most prominent, many not even using the positioning facility - GPS time is used in many applications.

Most of us who know its capabilities, and limitations, accept that GPS works in practice. It would appear that this is not good enough for some, and they are trying to get GPS to not work in theory......:hmm:

[Riverboat]

411A and Reynoldsno1 - spot on! Pity you don't work for the CAA.

[ShyTorque]

Blacksheep,

"Navigating with a secondary system is good practice and has been for centuries. There's not much effort involved in running a raw data cross check against an old fashioned paper map at regular intervals. How else can you be absolutely certain that your FMS is telling the truth?"

Exactly what we routinely do, that's how I knew it was accurate without GPS inputs. It's even easier when you have a moving map fed from the FMS, all that is required is to make a cross check that the displayed aircraft position ties in with a raw position from VOR/DME or NDBs.

The FMS even tells us when to change beacons on our Nav 1 box and which one it would prefer, although we do pre-empt it on most occasions because our routine checks keep us ahead of the game in that respect. We can go into various FMS info pages which tell us which satellites and ground based beacons it is using. It is usually working / computing from at at least half a dozen or so DMEs.

On this occasion, we could tell when the jamming ceased, because the aircraft symbol on the moving map twitched slightly, which probably related to about a hundred metres.

Obviously the concern is someone who might be placing too much reliance on GPS. If the whole system suffers jamming it immediately ceases to work at all.

[Blacksheep]

I know that's what you good navigators do ShyTorque its what the not so good navigators do that worries me. There's ample evidence in the preceding posts that there are quite a few poor navigators flying around the skies, some of them 'Professional Pilots' too!

As a long time and highly qualified avionics specialist I've yet to encounter any foolproof 100% reliable navigation system. No matter how good and reliable the GPS is, the airborne equipment carried in today's aircraft is the same old junk that we've always had in aircraft. If avionics systems were indeed perfectly reliable, I wouldn't have a job.

As a member of the Royal Institute of Navigation and avid reader of the Institute's Academic Journal I'm also well aware of the considerable shortcomings of GPS. It isn't anywhere near as accurate or reliable as so many people seem to think - which is why the Institute recommends caution when relying on it for primary navigation.

[derekl]

I suspect it's not widely known, but digital cellular systems rely on GPS to provide "master clocking" and time synchronization at each base station. Just another reason to make sure it keeps working. I don't imagine that European cellular operators will be rushing to switch their equipment from using NavStar to Gallileo just because of its European credentials.

[Belgique]

Anybody thought about the legality implications for the mass of EGPWS users who might have a CFIT if the GPS was suddenly switched off or degraded significantly?

Let's say that at any one point in time around 7500 EGPWS using airplanes are flying around and someone pulls the GPS plug, perhaps as a SCATANA measure.

a. What will the pilot see? Just a RAIM alert?

b. Will he realize that his EGPWS is defunct? What mode will it default to?

c. Having relied for years upon EGPWS to keep him out of rock-filled clouds, is he that much more of a CFIT risk?

d. Who sues who if there's a sudden batch of deadly CFITS during a GPS outage?

e. What about if a CFIT's claimed to have been due to an intentional Defence-related degrade of the system's accuracy?


SCATANA = security Control of Air Traffic and Navigation Aids

[411A]

<<EGPWS and SCATANA downing of GPS
Anybody thought about the legality implications for the mass of EGPWS users who might have a CFIT if the GPS was suddenly switched off or degraded significantly?

Let's say that at any one point in time around 7500 EGPWS using airplanes are flying around and someone pulls the GPS plug, perhaps as a SCATANA measure.>>

Ok, lets presume all this happened, Belgique, and all the EGPWS units in aircraft worldwide failed all of a sudden.

Hmmm, well, if you have to use EGPWS to avoid the rocky bits, then I guess you would be better off firmly on the ground.

Strange, ain't it.
Thousands and thousands of aeroplanes managed to avoid the lumpy parts simply by knowing where they are, flown by professional crews for many many, many years.

Gee, what a surprise... :uhoh: :uhoh: :uhoh:

[West Coast]

411
What is the trend of aviation safety from the 1960's till now? Safer or more dangerous?


I've seen a lot of posters talk about intentional shutdown and how it likely wouldn't happen. What about unintentional shutdown? MIJI anyone. Isn't an unintentional signal loss enough to make sure you know where you are independant of GPS?

[Carnage Matey!]

You don't need GPS to use EGPWS. I've flown plenty of aircraft that have EGPWS fitted but not GPS. You just need to make sure you do nav accuracy checks to ensure the FMS/IRS position is within tolerance compared to the raw data position.

[West Coast]

"You don't need GPS to use EGPWS"

Can you say with any authority this applies to all avionics suites?

[Carnage Matey!]

Absolutely not, but we fly a fleet of A320s and B744s that are EGPWS but non GPS equipped so clearly it can work without GPS.

[UNCTUOUS]

Carnal Matey! said

You don't need GPS to use EGPWS. I've flown plenty of aircraft that have EGPWS fitted but not GPS. You just need to make sure you do nav accuracy checks to ensure the FMS/IRS position is within tolerance compared to the raw data position.

Perhaps you should review these two links:

LINK ONE (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/no-GPS.html)


LINK TWO (http://www.iasa.com.au/folders/Safety_Issues/RiskManagement/toolow-terrain.html)

[Groundloop]

"I can count on exactly three times when the GPS signal faded or was not available...and never during an approach to GPS minimums"

So, 411A, let's get this right. You have experienced GPS becoming unavailable - so it is NOT 100% reliable. But because it happened not to be at a critical phase of the flight - it's all right then. Aren't you the lucky one! What if it had occured at a critical phase of the flight?

One major problem with GPS is if one satellite begins to transmit rubbish. This can result in incorrect positions being calculated and may take time to be detected and the satellite switched off or the constellation health message upgraded to broadcast this fact.

That's why there are systems like EGNOS which have fixed receivers at known positions constantly monitoring their GPS derived positions and immediately broadcasting notification of GPS unreliability. If GPS was perfect EGNOS (or WAAS and LAAS) would not be needed.

It's not a "not invented here" syndrome in Europe. It is more of a "it WAS invented here" syndrome in the US and therefore it MUST be perfect. Fact is, it isn't! And where lives could be at risk sticking your head in the sand is not a professional approach.

[411A]

<<So, 411A, let's get this right. You have experienced GPS becoming unavailable - so it is NOT 100% reliable. But because it happened not to be at a critical phase of the flight - it's all right then. Aren't you the lucky one! What if it had occured at a critical phase of the flight?>>

What?
You have never heard of INS becomming unreliable?
I have had two out of three fitted failing more the once certainly, yet we pressed on with the flight, using other modes of navigation.
Just because 'it' might fail enroute, is no reason to get in a panic, now is it?
For approaches, there are VOR's and ILS's available, and indeed the odd diversion might be needed.
All in the name of the game of professional flying.

Now, I can understand why younger guys might have a slight 'problem' but those of us who have been around awhile, manage to cope.
Then we come to map shift on several types just a few short years ago.
Did these guys panic, and have a fit?
I suspect, surely not.

[reynoldsno1]

One major problem with GPS is if one satellite begins to transmit rubbish. This can result in incorrect positions being calculated and may take time to be detected and the satellite switched off or the constellation health message upgraded to broadcast this fact.

Which is precisely why IFR certificated aircraft receivers have their own integrity monitoring and warning ssytems... and why those States experienced in the use of GPS have developed and implemented technical, training, regulatory and operational procedures to ensure safety of flight......

[UNCTUOUS]

The first modernized GPS satellite meant to provide significantly improved navigation performance for civilian users worldwide, and U.S. military for its special purposes, has been put into orbit.

The satellite is the first in a series of eight GPS IIR-M satellites that will offer a variety of improvements for GPS users' once initial operational capability is reached. This latest series will offer a variety of enhanced features for GPS users, such as a new antenna panel that provides increased signal power to receivers on the ground, two new military signals for improved accuracy, enhanced encryption and anti-jamming capabilities, and a second civil signal that will provide non-military users with an open access signal on a different frequency that should improve its capability for critical navigation purposes.

The current GPS constellation of 28 spacecraft includes 12 fully operational Block IIR satellites, which were previously developed to improve the global coverage and overall performance of the system.

The dash M satellite, built by Lockheed Martin for the U.S. Air Force contingent at the Navstar GPS Joint Program Office, was launched aboard a Delta II rocket on September 25 from Cape Canaveral in Florida. 10-02-2005.

[pantyripper]

My 2 cents worth....Try using the damm thing in my neck of the woods and you might change your ideas on GPS reliability. We fly GPS NPA into a field with no other aids and have failures on a regular basis, lucky for me the other side kept working, but we do have times when both sides fail, luckily in VMC though. But still my company insists that it's nothing to be worried about, especially the high terrain ....which they say is depicted on the EHSI via the TAAD of EGPWS, .....I guess not. God knows how we got approved to do the approach?:}

[OzExpat]

God knows how we got approved to do the approach?
I'm not God, but I'll take a wild guess at the answer to that. It probably had a bit to do with training, certification, maybe even some periodic proficiency checks, and procedures in your Ops Manual that talk about action in the event of non-availability of GPS.

If that isn't enough and if, as I suspect, you're in Oz and using TSO C129a gear, then you need an alternate that has a serviceable navaid. But then, I'm sure you knew all of that already. :}