NDB lament.
 

I trained on steam gauges (there was nothing else then) and have just recently gotten a little more used to GPS. The 12.000hr (I kid you not) rental 152 I fly out of Lydd is all old school - not a GPS in sight. It barely has a VOR.

I don't mind this at all, but one of the things I always used regularly on aimless flights was the ADF, just as a little pointer and guide to where you were so you don't have to be buried in the chart all the time. I like ADF - it's simple and useful. But these days, they're on the chart, you tune them, but rarely do they work.

Is there some kind of list of when and which NDB's they plan to shut down in the near future? And how long before they'll all be gone?

NDBs work as they always did - assuming you have a working ADF which is not a common feature of rental wreckage.

They are just not that good when there are terrain assymetries about; coasts, hills, etc. The Lydd NDB is a joke... one can fly a perfect straight-in approach (GPS/autopilot coupled) and watch the ADF needle on the RMI go all over the place.

Maybe the ADF is crap in the aircraft, but I seem to miss more than I hit, even when I'm real close. I seem to remember that many had been shut down - the ones at Gatwick, for instance. The one near Headcorn (or is it Rochester? - I don't have my chart handy) never tunes, even real close.

Proper use of the ADF

1) Select NDB as waypoint on GPS

2) Enter desired track to waypoint

3) Fly the little white airplane up the magenta track

4) Tune ADF to 60's Rock and Roll station

5) Enjoy better flying through high technology and the last decade of good music

Really with used portable GPS units available for the same price as a good headset, I do not understand why pilots deprive themselves of the most accurate positional and navigational information available (backed up with a map of course).

If the NDB is on the (current!) map and/or in the AIP, and is not Notamed to be U/S or withdrawn, then it should be working. Otherwise it's a flight safety issue and you should not post about it on this forum, but write to the CAA about it.

But I have to agree that strange things happen sometimes. There's a DME "FRT" in the Netherlands (co-located with the RR NDB) which hasn't been printed on the "official" ICAO map for years now. But it is on the Jeppesen VFR map, it's also in the AIP and when we tried to use it a while ago, it worked just fine. It's also not part of any SID or STAR. A real mystery DME that only Jeppesen seems to know about.

Jeppesen "know" about a number of NDBs ;)

I think it's because in N Europe there isn't a great shortage of nationally produced VFR charts, so not many people buy the Jepp ones, so mistakes do not get reported to Jepp.

It's like the old Bottlang VFR touring guides. They were full of mistakes.

Don't forget NDB's DOC vary from one station to another, GPS is great but take a scenario such as this for example. Azores perhaps, locator approach, no GPS approach published or no RAIM for whatever reason....it soon becomes a very useful aid! Obviously backed up with whatever you can get a signal from!

Yes, a GPS ;)

Obviously one would fly an NDB approach using the GPS OBS mode.

We seem to be in a technological no man's land in some respects. ADF/NDB systems that are approved but are unreliable and GPS systems which are reliable but unapproved!

Surely this can't be the old worry that someone might degrade GPS or switch it off!?

I know it would be expensive to change over to modern systems but its going to happen one day and the benefits are already in evidence.

KR

FOK

IO540;

I think what Gardener is referring to is the abysmal GPS coverage at the Azores.

It can get so bad there that the NDB is the only reliable aid, GPS is often either RAIM unavailable or "GPS signal was lost ..... seconds ago"

I heard a rumour last week that all en-route NDBs and VORs will be phased out by 2018. (Note the word RUMOUR in that last sentence)

Reliability of GPS is often overestimated. With the solar activity on the rise, many specialists predict more frequent loss of GPS reception in the coming years, and loss of reception due to aurora borealis is a fact. I am not trying to assert that ADF is any better, but relying on GPS alone does not look like good airmanship to me. Personally, I wouln't want to fly over the North Atlantic without a non-GPS backup to GPS - e.g. Loran (for lack of an affordable INS).

Surely not. The GPS sats orbit around the earth. They don't have a favourite place :)

IO540;

Sorry, from personal experience the coverage there really is less than adequate. Then again so are the SAR procedures and a host of other things, but the GPS signal is about the worst.

SND

Impossible..The satellite constellation orbits the earth at 12000km and so are always changing location and so there is no way that one place can have "abysmal GPS coverage"....You may get the very odd occurrence when the geometry of the satellites may be bad (Hence Dilution of precision - DOP, for example PDOP and HDOP) - perhaps one has gone down for example, but there are so many now (30 something?) that even if this did occur then it would only be for a brief time (order of minutes) and you should still get 3D nav accurate to 100m. The great thing is that the GPS receiver tells you this too! UNlike an NDB which the only way to work out when it is not working is to keep indenting it all the time.

...unless you have an ionospheric anomaly over this particular location. Such anomalies are more frequent at high latitudes but in principle may occur anywhere.

I have just been to Eurocontrol's RAIM prediction website and there are currently 10 satellites visible from the Azores. Also did a RAIM check for Santa Maria Airport on the Azores and there are no RAIM outages.

Atmospherics could explain it, but I doubt it. I have worked in the Barrents Sea, and even during really strong solar flares and Northern Lights everywhere I have only ever seen the GPS drop out for a second or two....

GPS fitting and antenna location are more likely to play a role in these outages....

My questions is much more sinister: how does the GPS satellite know where it is?:}

Apologies, my point was more that in the Azores many of the procedures are Locator or NDB which is why I used that example, not necessarily you will have more problems there. I agree with englishal that much comes down to "fittings".

I0540 Yep! I would back it up with GPS if available, if the kit is available then use it....we also have the added benefit on some occassions of the Flight Inspectors equipment down the back for a 3rd opinion!

Sir Niall....

It's no rumour, see details here.....

http://www.ukfsc.co.uk/files/Consult...Aug%202009.pdf

Not all VORs affected, but most NDBs.

Am I correct in understanding that the GPS satellites can be moved around to suit the requirements of the people who own them i.e. the US military? So if they have operations somewhere they may move the satellites to improve coverage there and potentially leave other areas uncovered?
I remember many years ago when the RAF attack squadrons first got Tornado one of the navigators saying he still carried a map because you'd feel a fool without one when all the kit failed. With that attitude in mind I flew a one hour VFR nav' in Southern England last week using VOR, DME, NDB, looking outside with the map and with the GPS on just in case. Then again, I'm not a sky god so like the reassurance :)

No..........................

GPS

The GPS satellites are not in geostationary orbit so they have to move about (as seen from the earth) otherwise they'd just fall from the sky. So the military cannot simply move a few satellites from one location to the other, and then keep them there. The only thing they can do is alter their orbits.

There are six intersecting orbits defined, each containing four satellites spread evenly throughout this orbit. The net result of this is that between 6 and 12 satellites are visible from any point on earth simultaneously, assuming that you have a full view of the sky in all directions. But you only need to see four satellites for a reasonably accurate position fix (measured in meters). In that sense, there is no need for the military to move satellites about at random to improve coverage somewhere.

On the other hand, due to the earths uneven field of gravity and all sorts of other cosmic influences, satellites do deviate from their designed orbits. Plus, there are some satellites stacked as 'spares' in higher or lower orbits, ready to take the place of any failed satellite. And if a satellite fails, it has to be moved to a graveyard orbit. For this purpose all satellites will have little booster rockets on board so that the orbit can be adjusted.

GPS satellites regularly broadcast their designed orbit (the "Almanac") and even their current deviation from their defined orbit (that's part of WAAS I think). Your GPS receiver uses this orbit information plus the precise timing signals to determine your position.

So as far as the satellites are concerned, GPS coverage across the globe, including the poles, is fairly consistent and there's no need to adjust the orbits to improve accuracy somewhere.

But there may be atmospheric or terrain issues that cause a degradation in signal. Plus, it's possible for the US military to disable or scramble the GPS signal when the satellites are over a certain area (active warzones for instance) although this will probably limit the Americans ability to wage war too. And it's possible to install local transmitters on the ground which broadcast on the same frequencies as the satellites, leading to local jamming of the signal.

LORAN was shut down in the US late last year.

IRRenewal, not last year, but a month and half ago, and only in the US; Canada will decommission its network in October. European countries reconfirmed their intent to proceed with further development of eLoran (enhanced Loran with built-in low-speed datalink to transmit corrections). Russia does also maintain its Loran-compatible Chaika network. Furthermore, International Loran Association claims that elements of Loran-C infrastructure with a potential for use in eLoran will be retained in the US as well.

Adam
 

To go back to the origanal point of the thread, I have to agree with IO540 in the fact that not enough money has been spent on maintaning the aircraft you are flying for years.

The problem is that a lot of aircrafr have the King KR85 ADF fitted, in it's day it was a good unit but with out product support from King it is getting very hard to maintain these units and with the end of ADF not far away the £4000+ bill for fitting a reliable King KR87 ADF it is simply not worth doing.

I have found myself in this position as I have an aircraft with a KR85, A pole of my customers indicated that they would rather have an IFR GPS fitted at much the same cost.
The other aircraft that I rent out has a KR87 that works just fine by ADF standards.

BP, that's not quite right. Ground stations track all the GPS satellites and the information is used to predict the orbits (ephemerides) of the satellites. This information is transferred to the satellites and broadcast to GPS receivers.

More information here: http://is.gd/b7l7k
WAAS (Wide Area Augmentation System) was developed by the FAA to provide corrections to GPS signals to improve the accuracy of the signal to allow Cat 1 precision approaches. Ground reference stations are used to calculate correction factors which are broadcast from a geo-stationary satellite. WAAS-enabled GPS receivers use this information to refine the calculated location to an accuracy of typically 1 m horizontally and 1.5 m vertically.

A bit more about WAAS and Differential GPS....

The ground reference station is located at a very accurately known location (surveyed), say on an airport for sake of argument. This reference station also receives the same GPS signal as is received in the cockpit by the GPS. The ground reference station then compares the position derived from the raw GPS with its known location and calculates any error, then re-broadcasts this error (via RF, satellite, Spot beam etc....) so that the GPS in the cockpit can "correct" its position by applying the same error correction. This can actually achieve millimetric accuracy if the GRS is relatively close to the GPS it is correcting.

You probably won't have a reference station right in your vicinity so when using differential GPS then a number of GRSs are normally used which may be located hundreds of miles apart and the results of all of them are averaged to give an overall correction to apply to the GPS. This was particularly useful in the old days when the US military used top apply selective availability to the GPS signal to deliberately introduce errors to keep accuracy above say 100m. Using reference stations one could pretty much "undo" a these errors to give 5m or so accuracy. Back in 2000 the errors were turned off and Clinton signed a memorandum stating that the US would not turn off or scramble GPS signals again.

Rather than invest in their own system, I think Europe should have offered to invest in GPS and possibly shared some of the control over it, and maybe even have a second control centre in somewhere like Geneva, which would ensure its integrity, rather than re-inventing the wheel which is what seems to be the Euro way....GPS is a standard, and is always going to be better than any new system, so why not just help improve it rather than waste billions on a new project.

The European version of WAAS is called EGNOS.

The EGNOS signal has been receivable by handheld GPSs for a few years but IFR (panel mounted) units have bizzarely been prohibited from using it.

However, this has just appeared on some other forums

Dear EGNOS user,

The certification of the ESSP SAS as an Air Navigation Service Provider is progressing according to plan and is expected to be completed by the second half of this year. Once the ESSP SAS is certified as an ANSP, the message type 0 will be removed from the EGNOS Signal in Space. After an initial observation period (around 1 month), the EGNOS Safety of Life service will be declared ready for use. After this milestone, the corresponding ANSPs will begin the publication of GNSS RNAV procedures based on EGNOS, many of them currently under development. Therefore it is expected that several GNSS RNAV procedures will be available for use in Europe before the end of 2010 and many others will follow during early 2011.

Best regards,

The EGNOS Helpdesk