i had a little problem with the spark, it went into Atti mode managed to land fine. when i got home i checked the flight log and at the time it changed i had 12 satellites, it had dropped fron 16. i have phantom 3 std and i have no problems when i have just 7 satellites. is the sparks gps that sensetive that it changes mode.
thanks in advance

In order to fly your drone you need 6 satellites, because these aircraft use both glonass and gps a satellite count 11 should give you just enough to fly. Ie 6x gps 5x glonass so while it tells you it has 11 it may only be using 6.
At 12 you should be ok but might be getting warning of weak gps or you might even be getting compass problem which will cause Aircraft to go to Atti mode.
If you want to get a better idea of what happened you could upload your log to link below just click on link and follow instructions come back here and post your link.

http://www.phantomhelp.com/LogViewer/Upload/