I'm not sure. It's very unusual to see even low levels of potential interference in that area. Looking at detailed stats using the history feature of GPSJAM PRO, I'd say it's likely there's a real effect that is having an impact on a significant percentage of aircraft in that area. It's true it can be tricky to figure out exactly what it is having an impact.
"# Good" is the number of distinct aircraft that flew through that hex that never reported low accuracy with their GNSS. "# Bad" is the number of distinct aircraft that at some point during their flight reported good accuracy with their GNSS, but some time after that, including while flying through that hex, reported low accuracy. I would say that based on the number of aircraft showing up as Bad, and the fact that it's just that hex seeing this effect, it's likely to be showing a real effect.
My list of the most common things that make an aircraft report low GNSS accuracy:
1. Intentional GPS jamming.
2. Unintentional GPS interference.
3. Aerobatics that cause the aircraft's GPS antennae to be masked from satellites by the body of the aircraft.
4. On-board equipment issues.
I think the data suggests it's not #4. #3 is typically seen in military operating areas (MOAs) in the U.S.; I don't know if there might be fighters practicing in the skies west of London.
Edit to add: FWIW I've gotten one report from a person in the yellow hex that they weren't able to get a GPS fix. That's all I know.
As others have said, more likely dodgy methodology by gpsjam than anything sinister.
For example:
- As well as being an active airfield, Heathrow also houses a small number of maintenance bases (e.g. BA have one, United are currently upgrading an ex-Virgin one etc.). I'm not familiar with aircraft maintenance, but I suppose there could easily be scope for RF signals related to test procedures to be leaky and be picked up by geeks.
- There is also Farnborough. Whilst Farnborough is predominantly a GA (General Aviation, i.e. private jet) airfield, it is also on of the many homes of QinetiQ in the UK. QinetiQ being a defence contractor. So again, one could speculate about leaky test signals.
There's Windsor Castle near the green area of the center (Windsor Grey Park). And some related military installations close by. Easy to see why it would be jammed...
No. There wouldnt be jamming of civilian navigation right next to one of the busiest airports in the world. Most likely cause is lots of gps warming up at lhr.
No. As another commenter mentioned, if that were the case you would most likely see it at other airports, and you don't. Additionally, the data that GPSJAM shows is filtered so that an aircraft isn't considered to have "bad" accuracy unless it has first reported "good" accuracy recently.
London is the busiest "airport system" in the world and handles a lot of international traffic, so there might be something unique about it that you don't see somewhere like Atlanta.
That being said, it seems like London only has interference recorded today and every other day is green. I would imagine it's more likely to be a quirk of how the data is recorded rather than geniune jamming.
Not sure how you measure busy, but Atlanta handles way more passengers than London. It may be that London has far more flights due to the use of smaller aircraft however.
Do they use ground mlat there? That is the only reason i can think of that you would get cold gps transmitting. Lht was first operational ground mlat site, but i cant find a current list.
This gpsjam site doesnt have much info on methodolgy. Seeing the data would probably show what is causing this issue.
