Anyone else suffer regular GPS failures?

[Oscar Kilo]

Hi again all,

As a good weather VFR only type of PPL I enjoy dead reckoning as much as the next man and always thoroughly plan my routes, mark up the charts accordingly, and monitor progress on my PLOGs. Additionally I also have a Garmin GPS 3 Pilot and another Garmin GPS 89 as a backup incase my batteries packup in the main GPS. Like most people I find the GPS a fantastic gadget to backup my visual nav, and on many occassions the GPS has put me right when "temporarily uncertain of my position" (ie lost!).

Since using the handheld GPS units (around 4/5 years) I have had several occassions when the devices have failed. It's not usually that one stops and the other works but they tend to both fail together - usually following a "poor GPS coverage" message. On Monday evening for example when flying some non-pilot pals around the Milton keynes area both units had no significant satellite lock and the GPS 3 said "power down and re-init" - which incidentally doesn't cure the problem!

This probably happens in one in ten flights, fine when I know where I am like Monday but not much fun if I'm going somewhere new (hence my belt'n'braces approach with charts etc).

Does this only affect me so frequently or do others have similar problems? I am using the units inside a PA28 resting on the "dash" with the antenna pretty much vertical. I'd love to know if anyone else has such frequent issues with their handheld GPS whilst in the air. Test runs in the car by the way always work fine!!

I so often read about people relying on their GPS all the time, I certainly dare not rely on mine!!

Looking forward to your comments,

- Andy.

[yawningdog]

A remote aerial with window suction should give you better reception than a fixed aerial.

[QDMQDMQDM]

It's never happened to me using a GPS3 with its own aerial on the dash, but as a control freak neurot I could never sit there, relying 100% on a GPS and not being able to pinpoint my position on a map. That would be highly silly and it's hard to believe people do that. A GPS is an aid to nav and a bloody brilliant one, but it's only an aid. A GPS can give up and go AWOL, a map can't (unless you're in an open cockpit!).

QDM

[Cusco]

I started off my GPS usage years ago with a Garmin GPS90 using the integral ariel in a P28R. and yoke mounted.(which I still keep powered up as Back up.)

IIRC it only uses 8 satellites and regularly dropped out around the north norfolk coast above Coltishall.

I then switched to GPS295 still yoke mounted but used the remote ariel at the front of the screen in the P28R.

Never had satellite drop out since, all over S england and halfwaydown France.

But don't know if this is due to greater number of satellites used in GPS 295 (12) or use of remote arial.Worth trying remote arial well up front.

Just my two pennorth

Safe Flying
Cusco

[StrateandLevel]

In most cases this is due to an inadequate antenna, the signals can be screened by the aircraft depending on the sattellite position and finally it gives up.

Another cause is your VHF radio which can switch off the GPS antenna loosing the signals completely. Most GPS antennas are "Active" that is, they are a simple antenna with a transistor amplifier built in. They are broadband to strong signals and when presented with a nearby transmitter, the amplifier saturates, and goes from being an analogue amplifier to a digital switch, dissconnecting the antenna from the receiver. Antenna location is important.

[Monocock]

Oscar Kilo

Interesting subject. I too attach my Garmin III on top of the coaming of my PA28 and have all sorts of problems sometimes.

Recently however, the problem isn't so much lack of "reception".

What seems to happen is the unit just turns itself off for no reason whatsoever. Sometimes it's every 10 minutes other times it doesn't happen for an hour or two.

Any one else find the same?

In frustration I once whacked it on the floor of the plane and it seemed to behave itself then for a few days!

:}

[QDMQDMQDM]

What seems to happen is the unit just turns itself off for no reason whatsoever. Sometimes it's every 10 minutes other times it doesn't happen for an hour or two.

Yes. Contact Garmin. They will give you a little spacer to put between the two sets of batteries for free and that will cure the problem. Basically it's a design fault and sometimes the batteries come loose. I had it myself.

QDM

[vancouv]

I've got a Garmin 196, and it won't work properly without an external aerial. If I have it in the plane with just the attached aerial it frequently loses the signal.

Since having it mounted on the yoke with an external aerial that is attached to the window with suckers, I have never had a problem.

As an aside, if you put your GPS on the dash aren't you in danger of upsetting the magnetic compass?

[Mark 1]

Its not happened for a while now, but I have often lost reception in the Midlands, especially between approximately Coventry and Banbury.

This has been with both 295 and III Pilot recievers.

I've suspected either saturation due to radio transmissions (Rugby?) or some other kind of jamming.

During these drop-outs all sattelite signal strength levels seem to drop off. If it was a satellite/ariel position problem, I would still expect to get a good signal from some satellites.

[IO540-C4D5D]

Oscar Kilo

You should use an external GPS antenna (aerial) - even if it is only the one which attaches with a suction cup to the unside top of the windscreen. The built-in antennas on Garmins are often marginal in an all-metal plane.

I have twice had GPS signal loss, lasting about 20 secs, in a very specific place in the South East, with a Bendix/King handheld. Presumably there is a powerful transmitter there which saturates the GPS receiver. But never seen it with a KLN94 with a proper rooftop antenna.

When you look at the ease with which you can become "uncertain of position", a GPS is far more reliable than any other way of navigating.

[Oscar Kilo]

Thanks all for your comments, interesting stuff.

There is an external Garmin antenna on the outside of the aircraft which I guess I should ideally use, I've just not got round to making up a BNC connection lead I can use to join my GPS III to it yet - anyone have any hints as to the type of coax I should use for such a flylead?

IO540-C4D5D - I do have one of those rubber suction cup accessories but haven't really been able to find a spot that seemed worth using in the PA28 - thinking, perhaps in error, that it was best to keep the antenna vertical and the suction cup at the top of the windscreen means it's at quite an angle. Given so many of you reckon this will help I will of course try it next time I fly.


Mark 1 - I'm with you on this, my symptom is that one minute it's working fine with strong signals form approx 6-8 satellites and then over a period of around 30 seconds they all fade away to virtually no signal strength and I start getting the "power down and re-init" or "poor satellite coverage" error. I tend to do 90% of my flying west of London in the Midlands area (South of Milton Keynes, North of Basingstoke and East of Newbury). I too have wondered if strong local signals were to blame or specific jamming, those frequent NOTAMs you see citing "GPS Jamming Trials" seem to be a clue but it's a pig to work out the area they are supposed to affect and when they are operating.

Anyway, thanks again all, I'll take up some of these suggestions and report back.

Safe flying!


:ok:

[IO540-C4D5D]

Oscar Kilo

I clearly remember from my GPS user manual that the suction cup antenna should be mounted with the curved surface facing the sky. Yours may be different but there ought to be instructions for this. The antenna certainly should be mounted with "a" flat surface facing the sky.

The coax used for VHF, UHF and GPS is all 50 ohm cable. This is common as muck; however for the connection to the GPS itself you may have to use something much smaller than a BNC plug and a rather thin cable might be needed; however you can still get 50 ohms. Go for a low loss type.

I used the suction cup antenna in a PA28 for every one of my 60 hours in them :O I stuck it to the very top of the windscreen, where the material is almost horizontal. Worked great.

[Shaggy Sheep Driver]

When I first bought my Pilot 111 it occasionally switched itself off, so I returned it to the supplier who replaced it. The replacement has been fine.

Regarding signal loss, I have only once encountered this. I was RH seat in an AA5 above cloud over the Lake District. Both me and the P1 had our Pilot 111s, and both units simultaniously lost signal. P1 had a remote aerial, which we tried in every possible position. I tried holding my complete unit at all available windows - to no avail. They both recovered at the same point about 30 miles further north. There was no notamed deliberate jamming, so it remains a mystery.

I usually use mine in the Chippy, mounted on the coaming. The perspex canopy means I get a good signal withpout the need for a remote aerial.

SSD

[DFC]

If the GPS 3 looses signal, turn off the other GPS to see if that cures the problem or try flying in the same areas using just the GPS 3.

I had this problem with using a GPS 3 and a pannel mounted (old) GPS. The GPS 3 even had problems with the antenna extension.

The answer which was given to me was that the internal clock of the other GPS was radiating a signal which interfered with the GPS 3.

As long as I keep the pannel mounted GPS off, there are no problems with the GPS 3.

Regards,

DFC

[Windy Militant]

Had a nice man from the CAA give a talk about GPS to one of my local PFA groups. Apparently it's very easy to jam GPS signals and jammers are apparently available in the USA. He also said that in Boston (I Think) harbour there was a complete loss of GPS for a three mile radius which was eventually traced to a harmonic side band signal being emitted from a Radio Shack TV aerial booster that someone was using in the marina. So keep that finger on the map;)

[IO540-C4D5D]

A GPS can also be jammed with a DME tuned to a specific frequency which has a harmonic on the GPS frequency. There is some material on the www about this.

Another reason for having a plane with a rooftop GPS aerial, and preferably a metal roof, or (if composite) mounting the GPS aerial on a metallic surface. Plus of course very good shielded cabling on both the DME and the GPS...

[Jeffrey]

Just one point that you might also check with regard to reception - this site..........

http://augur.ecacnav.com/Augur_Area_Selection.htm

will give you RAIM predictions for UK/Europe, and will show any holes and their expected duration.

Not related to this thread but I have noticed on my 196 that the control zone around London does not appear.

I have the Jan/Feb 2003 database download, and on enquiring from Jeppesen in Denver was told that there is currently an incompatbility issue between the way in which Jeppesen scan their data, and the way Garmin transmit it.

I would have thought that this should raise some concerns on what information we are currentlt presented with.

Anyone else have this problem?

[A and C]

I have been using IFR aproved GPS uints for the last 7 years or so and have not had it drop off line for more than 10 min in the whole 7 years except for during the Iraq war when it was off line for a whole day ( to civil users )

I am sure that all your problems are due to the GPS signal not getting to the unit as the signal is so week the aerial positon is critical both to see the signal and to be free from harmonic jamming from the VHF comms ( and DME ? ) the other thing that can give trouble is the gas dicharge display transformer inside the radios fitted to the aircraft.

This problem is normaly only found with Narco radios and can be fixed at modest price by Gatwick avionics at Stapleford.

[Oscar Kilo]

A+C - Interestingly enough the PA28 in question does indeed have Narco Nav/Comms fitted.......

Remote aerial it is then.

Cheers,

- A.

[A and C]

Yes the first move should be the remote aerial and if that dont work then it is time to attack the Narco.

If you do have to do the Narco thing PM or Email me and I will point you at the expert in this Field.

[skydriller]

I have a new Garmin 196, and I think its the dogs doo-dahs....but...

1. I changed the batteries in it for the first time the other day, and during the subsequent flight the damn thing kept switching itself off all by itself, just as someone earlier mentioned. When back on the ground and after a little investigation of the problem I discovered the new batteries (unlike the old ones) could move slightly within their slots so as to break contacts. The aircrafts vibration must have caused this to happen & it to stop working occasionally. I inserted a 5mm thick piece of foam between the removable back and the batteries, padding it like this prevented battery movement and it has since worked fine - obviously not all makes of batteries are exactly the same dimensions.

2. I recently downloaded the latest Garmin 196 software update, unfortunately the airspace is glaringly wrong just where I happen to live. The controlled airspace changed around Bordeaux in mid March, the Jeppesen Map of France shows the correct airspace arrangement, but despite waiting until the beginning of this month before downloading, the download still had the old airspace... but how come if the Jepp map was correct?!?!
:confused:

Regards, SD.

[Mr Wolfie]

Skydriller - were the new batteries NiMH rechargables?

I ask as most brands of these that I have used (Kodak, LLoydtron, etc are slightly smaller in diameter than ordinary duracells and therefore do rattle around a little. Wrap a post-it note around each battery and it cures the problem. They appear to be the same length so I can't imagine why they would lose thier connections though.

Mr. W

[skydriller]

Mr Wolfie,

I actually replaced the batteries (cant remember the brand – sony?) with a set of Duracells....:hmm:
It is indeed a case of the diameters of the batteries letting them move around, hence my use of a little foam, which compresses down between the batts, but I will have a go with post-its if I find any problems with the foam idea.

Regards, SD.

[mad_jock]

Around our area we also get GPS dropouts all the time.

Its usually linked to a FRA plane on exercise.

MJ

[skydriller]

Well, I sent an Email to Garmin about the Airspace errors I had noticed, and this is their reply:

"Dear Sir,

Due to being informed of changes in how the Jeppesen database is created for us to use it has put us behind the power curve on correctly implementing the data in a format usable by our equipments. We have had many challenges with the new database formats but it will be resolved in cycle 0307. Please find attached a free code to use for this cycle so that everything will be back to normal. It is mainly an issue of Class D airspace that is the problem. We apologise for this.

Best regards

Steve Gubbins
International Sales Manager"

Just thought I would post this so that those of you considering getting an update know to wait until 0307 cycle, and I thought it was pretty good service of them to give me an update for that cycle too.:ok:

Regards, SD.

PS - MJ, stupid question I know, but what is an FRA plane?:confused:

[mad_jock]

FRA are based out of Teeside and they carry all sorts of nasty kit on them.

They fly around in Falcons with what look like missiles under there wings but actually they are ECM pods for playing with the military. Part of there job some times is to jam GPS, but as i know of 3 local lads with GPS jammers which they bought for 30 quid. I don't put much faith in steady signal for GPS.

They also have the job of calibrating all the instrument approaches in the UK.

You will hear them use the call sign calibrator.

MJ

[Sensible]

I have a Lowrance Airmap and it often loses position during turns. I have tried using it with the ariel mounted on the GPS secured to the yoke mount, I have tried it with the ariel remote stuck to the canopy with the sucker provided but the result is the same. In hot sun, the plastic on the sucker becomes soft, the receiver tips from the horizontal and position is lost more frequently. The worry is that sometimes the receiver commences a cold start cycle and so the GPS is useless for around 15mins.

[IO540-C4D5D]

Sensible

That is a very old GPS design, about 10 years old. I think you will find that performance has moved on a long way since.

However most aviation GPS products on the UK market aren't that much younger; there is very little innovation going on for some reason.

A roof-mounted GPS antenna should always be used; the school/syndicate may not want to pay for it (£300 or so) but it will benefit everybody who uses a GPS (which is almost everybody when there is no instructor in sight :O )