Why use other navaids when there is GPS?
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Why use other navaids when there is GPS?
Probably a stupid question here... Now that GPS is so precise and can be used in all parts of the world (as far as I know), why do aviators still bother with the radio navaids like VOR and NDB and not just GPS?? And why use IRS instead of GPS directly when the former needs to be corrected by GPS regularly??
Thanks for reply
Thanks for reply
The availability (or otherwise) of GPS is in the gift of the US government.
Does that suggest a reason why the aviation industry doesn't want to be 100% dependent on it in order to be able to fly from A to B ?
Does that suggest a reason why the aviation industry doesn't want to be 100% dependent on it in order to be able to fly from A to B ?
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Dave,
Actually as far as I'm aware it is no longer a "gift" of the US Government but rather a few years ago they changed the purpose of the system and it is no longer controlled by the DOD.
Of course it can still be jammed, but so can a VOR.
Actually as far as I'm aware it is no longer a "gift" of the US Government but rather a few years ago they changed the purpose of the system and it is no longer controlled by the DOD.
Of course it can still be jammed, but so can a VOR.
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FMC fail on a tricky SID out of a Spanish holiday island… ATC does not comprehend the request for radar vectors and just responds "standard departure". Doable, if prepared, with NDB and VOR raw data back-up
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Truth of the matter is that ground based NAVAIDS are almost relegated to history.
These days you can shoot an approach through a vally for many miles without reference to a single ground based aid, welcome to RNP AR.
These days you can shoot an approach through a vally for many miles without reference to a single ground based aid, welcome to RNP AR.
SkylineR34,
Because, while GPS may have sufficient accuracy for most purposes, the levels of integrity, availability and continuity required by aviation for it to be used as a sole navigation aid can not yet be guaranteed.
Because, while GPS may have sufficient accuracy for most purposes, the levels of integrity, availability and continuity required by aviation for it to be used as a sole navigation aid can not yet be guaranteed.
Last edited by Bergerie1; 8th Jun 2012 at 05:21.
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If nothing else, redundancy.
During a GPS approach today, I had a warning flag. Most likely it was our receiver, and not the system, however, the push of a button gave us a seamless transition to ILS guidance.
During a GPS approach today, I had a warning flag. Most likely it was our receiver, and not the system, however, the push of a button gave us a seamless transition to ILS guidance.
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And why use IRS instead of GPS directly when the former needs to be corrected by GPS regularly??
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If my FMC fails I lose my map-display, but the VOR/NDB needles and DME readings are still there.
If my LCD display fails I lose everything but my standby instruments. And these have VOR/NDB needles incorporated but no GPS info.
And of course the GPS receiver itself or the antenna can fail.
On small aircraft I had the GPS display freeze for more than 20 minutes on an IFR approved Garmin.
One reason is because the IRS can do things that the GPS doesn't. For example it is one of the sources for the IVSI, flight path vectors, trend vectors, wind calculations, wind shear detection etc. In modern aircrafts it is also the system that provides the displays with attitude information.
If my LCD display fails I lose everything but my standby instruments. And these have VOR/NDB needles incorporated but no GPS info.
And of course the GPS receiver itself or the antenna can fail.
On small aircraft I had the GPS display freeze for more than 20 minutes on an IFR approved Garmin.
And why use IRS instead of GPS directly when the former needs to be corrected by GPS regularly??
Last edited by Crankshaft; 8th Jun 2012 at 11:42.
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Anybody who has flown jets in close proximity to high terrain like The Alps, Rocky Mountains, Pyrenees, or other mountainous areas, knows that GPS has a tendency to glitch out or become inaccurate in these areas.
Now if there were only GPS approaches available to airports in these areas that would become a problem.
redundancy, the more the better in aviation!
Now if there were only GPS approaches available to airports in these areas that would become a problem.
redundancy, the more the better in aviation!
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Root,
Maybe you should have a chat with WestJet, they fly in and out of the mountains everyday... not using any ground based navigational aids.
The same can be said for Alaskan Airlines, the company that pioneered RNP AR operations.. It's two Captains going on to set up Naverus (now part of GE Aviation)
I can think of at least one example where a non GPS aircraft flying a VOR approach very nearly ended up in the side of a mountain. Not because of a fault of the crew but a faulty ground based navigational aid.
Maybe you should have a chat with WestJet, they fly in and out of the mountains everyday... not using any ground based navigational aids.
The same can be said for Alaskan Airlines, the company that pioneered RNP AR operations.. It's two Captains going on to set up Naverus (now part of GE Aviation)
I can think of at least one example where a non GPS aircraft flying a VOR approach very nearly ended up in the side of a mountain. Not because of a fault of the crew but a faulty ground based navigational aid.
Last edited by PT6A; 8th Jun 2012 at 12:06.
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Originally Posted by PT6A
Actually as far as I'm aware it is no longer a "gift" of the US Government but rather a few years ago they changed the purpose of the system and it is no longer controlled by the DOD.
From an article in a sailing magazine explaining why GPS cannot be relied on.
But GPS, the one system which is fully operational to date has more than it’s fair share of problems. The earliest satellites are now over twenty years old and the replacement programme is at least three years behind schedule land close to a billion US dollars over budget. This led to the US Government Accountability Office to issue a warning in May 2009 that the whole system could be at risk and that it may not be reliable in the future. And this isn’t the only problems the system faces. The main threat currently relates to the nature of the transmissions. Your GPS receiver collects information from solar powered transmitters which obit the globe at an altitude of 22,000 km – a situation which has been described by one expert to trying to see a car headlight at 12,000 miles! Consequently, the signals are very weak and also being very long with one complete transmission taking over 25 seconds, prone to disruption. In January 2007, the US Navy accidently blocked the GPS signal when two ships in San Diego harbour were taking part in a training exercise, causing chaos around the city. As well as the obvious disruption to navigation, the airport’s aircraft tracking system and port’s ship tracking systems failed, doctor’s emergency pagers malfunctioned, ATM machines stopped working and there were power cuts as the electricity supply failed to link into the grid.
GPS signals are also very easy to jam. But why would anyone want to jam such a crucial system? The Russian military blocked GPS signals when conducting operations in South Ossetia in 2008 so they could gain an advantage by using GLONASS. And the US military and forces friendly to the USA use them to deny their enemies positioning information , as they can use separate ‘P Code’ GPS signals which are more secure. Also, military authorities conduct GPS jamming trials in remote areas, but these are limited and published in Notice to Seamen. But the main reason why GPS is disrupted is found in the way it has infiltrated every aspect of our lives. Most smart-phones have it built in and many cars these days appear to have a small black rectangle rubber-suckered to the windshield. GPS jammers are available to purchase on the internet by those drivers who want to conceal their location from their employers who routinely use GPS based vehicle fleet management systems. And thieves have cottoned on to the fact that anti-theft tracking systems can be disabled by one of these gadgets. Costing as little as US$20, a jammer can plug into a car lighter socket and shield any GPS receiver within a radius of 20m from picking up the crucial signals. And more powerful ones can block signals in a 10km radius. In a recent incident, Air Traffic Controllers at Newark Airport in New Jersey noticed the GPS system dropping off-line at regular intervals disrupting air traffic. The problem was traced to a truck driver who passed close to the airport on his regular schedule and who was using a jammer to avoid paying highway tolls! And a new threat has emerged. Financial institutions use GPS signals to accurately time currency and trading transactions, which typically have a time window of three seconds. Jammers which can retransmit the signals a few nanoseconds later have been developed. This will shift GPS time enough for unscrupulous dealers to make a killing. Of course, as a GPS receiver calculates its’ position by resolving time signals, this will play havoc with navigation.
Another threat to the system is the demand on the radio frequency spectrum from other users. When GPS was conceived in the late 1970s, there were far fewer radio devices in use. Since then, we have seen the introduction of many other systems making demands on the available radio frequencies. Earlier this year, the US Federal Communications Commission allocated a frequency very close to the one used by GPS to ‘LightSquared’, a wireless broadband service which aims to cover 92% of the USA by 2015 using 40,000 ground based transmitters sending out signals stronger than GPS’s. The FCC believed that the LightSquared network would not cause problems for GPS and stated that it would not be allowed to operate unless testing showed that GPS systems would not be affected. However, independent testing suggests there is significant jamming in the vicinity of the LightSquared bases. And the signals can also be disrupted by natural phenomena – especially solar flares. These are on rise and forecast to peak in 2012. The solar energy entering the atmosphere can overwhelm the weak GPS data, particularly near the poles where the earth’s protective magnetic field is weakest. Reports of reduced GPS performance in these areas are already being received.
A very significant threat to all these satellite systems are the huge amount of man made “space junk” orbiting our planet. Recently, the US National Research Council warned the situation has reached “tipping point” and described a scenario where a collision between a satellite and junk could create a cloud of debris which in turn would escalate the problem, leading to whole systems being destroyed. When China tested an anti satellite missile in 2007, the target was blown into 150,000 pieces larger than 1cm in size – all of which have the potential to destroy another satellite.
Also, we shouldn’t forget that the GPS system is owned and funded by the US Department of Defence – and they have the right to restrict information to civilian users, or even turn it off at any time they wish!
But GPS, the one system which is fully operational to date has more than it’s fair share of problems. The earliest satellites are now over twenty years old and the replacement programme is at least three years behind schedule land close to a billion US dollars over budget. This led to the US Government Accountability Office to issue a warning in May 2009 that the whole system could be at risk and that it may not be reliable in the future. And this isn’t the only problems the system faces. The main threat currently relates to the nature of the transmissions. Your GPS receiver collects information from solar powered transmitters which obit the globe at an altitude of 22,000 km – a situation which has been described by one expert to trying to see a car headlight at 12,000 miles! Consequently, the signals are very weak and also being very long with one complete transmission taking over 25 seconds, prone to disruption. In January 2007, the US Navy accidently blocked the GPS signal when two ships in San Diego harbour were taking part in a training exercise, causing chaos around the city. As well as the obvious disruption to navigation, the airport’s aircraft tracking system and port’s ship tracking systems failed, doctor’s emergency pagers malfunctioned, ATM machines stopped working and there were power cuts as the electricity supply failed to link into the grid.
GPS signals are also very easy to jam. But why would anyone want to jam such a crucial system? The Russian military blocked GPS signals when conducting operations in South Ossetia in 2008 so they could gain an advantage by using GLONASS. And the US military and forces friendly to the USA use them to deny their enemies positioning information , as they can use separate ‘P Code’ GPS signals which are more secure. Also, military authorities conduct GPS jamming trials in remote areas, but these are limited and published in Notice to Seamen. But the main reason why GPS is disrupted is found in the way it has infiltrated every aspect of our lives. Most smart-phones have it built in and many cars these days appear to have a small black rectangle rubber-suckered to the windshield. GPS jammers are available to purchase on the internet by those drivers who want to conceal their location from their employers who routinely use GPS based vehicle fleet management systems. And thieves have cottoned on to the fact that anti-theft tracking systems can be disabled by one of these gadgets. Costing as little as US$20, a jammer can plug into a car lighter socket and shield any GPS receiver within a radius of 20m from picking up the crucial signals. And more powerful ones can block signals in a 10km radius. In a recent incident, Air Traffic Controllers at Newark Airport in New Jersey noticed the GPS system dropping off-line at regular intervals disrupting air traffic. The problem was traced to a truck driver who passed close to the airport on his regular schedule and who was using a jammer to avoid paying highway tolls! And a new threat has emerged. Financial institutions use GPS signals to accurately time currency and trading transactions, which typically have a time window of three seconds. Jammers which can retransmit the signals a few nanoseconds later have been developed. This will shift GPS time enough for unscrupulous dealers to make a killing. Of course, as a GPS receiver calculates its’ position by resolving time signals, this will play havoc with navigation.
Another threat to the system is the demand on the radio frequency spectrum from other users. When GPS was conceived in the late 1970s, there were far fewer radio devices in use. Since then, we have seen the introduction of many other systems making demands on the available radio frequencies. Earlier this year, the US Federal Communications Commission allocated a frequency very close to the one used by GPS to ‘LightSquared’, a wireless broadband service which aims to cover 92% of the USA by 2015 using 40,000 ground based transmitters sending out signals stronger than GPS’s. The FCC believed that the LightSquared network would not cause problems for GPS and stated that it would not be allowed to operate unless testing showed that GPS systems would not be affected. However, independent testing suggests there is significant jamming in the vicinity of the LightSquared bases. And the signals can also be disrupted by natural phenomena – especially solar flares. These are on rise and forecast to peak in 2012. The solar energy entering the atmosphere can overwhelm the weak GPS data, particularly near the poles where the earth’s protective magnetic field is weakest. Reports of reduced GPS performance in these areas are already being received.
A very significant threat to all these satellite systems are the huge amount of man made “space junk” orbiting our planet. Recently, the US National Research Council warned the situation has reached “tipping point” and described a scenario where a collision between a satellite and junk could create a cloud of debris which in turn would escalate the problem, leading to whole systems being destroyed. When China tested an anti satellite missile in 2007, the target was blown into 150,000 pieces larger than 1cm in size – all of which have the potential to destroy another satellite.
Also, we shouldn’t forget that the GPS system is owned and funded by the US Department of Defence – and they have the right to restrict information to civilian users, or even turn it off at any time they wish!
FWIW in Australia ....
http://www.pprune.org/dg-p-general-a...shut-down.html
http://www.pprune.org/dg-p-general-a...shut-down.html
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RNP AR with values of less than RNP 0.30 or missed approach procedures of less than RNP 1.0, require at least one IRU for "extraction" in the unlikely event of a loss of GPS during the approach. Otherwise, the target level of safety cannot be met.
