GPS fails over Shawbury
Last friday I routed via Shawbury to get up to Blackpool.
In the Shawbury vicinity, my GPS III began to misread, at one point telling me I had a Ground Speed of about 4356 knots (unlikely in a PA28). I was using it as a secondary aid, so had no problems.
After powering off and reinitialising the GPS, it seemed to recover approaching the Wallasey VOR. I thought nothing of it, and had no further problems to Blackpool and then on to Scotland.
However, on the return journey this Monday, exactly the same thing happened again around Shawbury. The GPS started working again about 20 nm south east of SWB.
Did I miss a NOTAM? Is there something special about Shawbury? Can someone explain this?