NOTAM about EGNOS LPV being unavailable

MAybe the geometry or system status of the satellites could not guarantee the required precision for LPV? Or a ground station had a problem?

EGNOS also uses land based stations for additional precision. The satellites (and those for GPS, Galileo, GLONASS) may be fine, the ground stations may have been inop (e.g. scheduled maintenance).

edit: I see that flyer59 already mentioned the ground stations and I missed that, sorry

EGNOS/WAAS absolutely uses ground based stations. These stations receive the GPS signals and, knowing their own 3D position accurately from a very accurate land survey, send back the error to a geostationary satellite(s) which send(s) back the EGNOS/WAAS correction signal.

The Q is why that particular airport was notaming the issue and not (presumably) every other LPV airport in Europe. The EGNOS geostationary broadcast covers a huge area.

If the issue was caused by a GPS outage then

• that would also not be localised, and
• all GPS approaches would be INOP, not just LPV

So my guess at the only possibility is that there was some kind of local jamming of the EGNOS signal (but not of the GPS signal).

If you wanted to prevent a small GPS-controlled pilotless aircraft from having enough accuracy to hit a specific small building then jamming EGNOS would do that. IMHO, without EGNOS, a quadcopter (etc) would not be effective for putting a bomb right on top of somebody’s house. The non-EGNOS accuracy is of the order of 5-10m.

Plus the military have the technology to shift the GPS position solution by some amount (by local “jamming”) and with EGNOS suppressed there is no way the GPS receiver would know, and if they shifted it only by say 50m then GPS would still be fine for LNAV approaches.

all GPS approaches would be INOP, not just LPV

do you think that is necessarily so? Since LPV uses a higher precision than the other WAAS approach LNAV/VNAV i can well imagine that the system simply couldn’t provide the necessary precisision,

With the US WAAS system, you can see the real time performance (updated every 3 minutes at this link) http://www.nstb.tc.faa.gov/RT_VerticalProtectionLevel.htm .
Within the last few days there have been solar storms that have affected performance and this might be relevant to the outage. See http://spaceweather.com/

Peter wrote:

all GPS approaches would be INOP, not just LPV

Not at all. A lack of precision could prevent LPV but not other approach types.

Peter wrote:

The Q is why that particular airport was notaming the issue and not (presumably) every other LPV airport in Europe. The EGNOS geostationary broadcast covers a huge area.

If the issue was caused by a GPS outage then that would also not be localised, and all GPS approaches would be INOP, not just LPV
So my guess at the only possibility is that there was some kind of local jamming of the EGNOS signal (but not of the GPS signal).

Peter,

There are periods of brief outages for LPV that have no effect at all on LNAV. The fact that the HPL degrades to 50 meters will have no effect at all on an LNAV procedure which only needs 556 meters. Even in the worst geomagnetic storms from CME from the sun, availability of the LNAV is 100%. I have only seen one case of an entire system failure for WAAS and even then the standard positioning service was available for approaches. So yes, one may get a downgrade from LPV, but it is extremely unlikely that it will result in the loss of GPS level of service required for LNAV. I have only experienced a single case of not having LPV available in 8 years of flying although it does occur. I have seen way more ILS outages and they last for days verses 10 or 15 minutes.

Again, a typical WAAS outage is caused by the integrity rising above a threshold. For WAAS LPV it is 50 meters for the vertical and 40 meters for the lateral, except when the DA is below 250 feet, in which case it is 35 meters for the vertical. So if the area is hovering around these values, some airports might experience a loss of LPV while others do not.

Looking at the US for the same period as the OP suggests there was a geomagnetic storm in play and it degraded the integrity of the WAAS and EGNOS during this time period.

@NCYankee what I don’t understand why they originally thought it would last 3 days, then after half an hour cancelled it. According to spaceweather, nothing much has changed at the sun, the CME is still there, there’s still an M class sunspot.

@NCYankee is this a degradation of the EGNOS/WAAS signal or a degradation of the GPS signal?

The former I can completely understand. The latter is strange, as is strange that an airport in Europe would even be aware of it since GPS is kindly provided by the US taxpayer How does the airport find out? Does an airport with a GPS approach have some kind of monitoring device or some kind of data feed from the USA which tells it if the integrity of the signal falls below some value?