Finally completed the “World Traveller” achievement (Land at 500 Different Airports) 
I decided to blitz the last 200 by visiting as many UK airports as I could as quickly as possible. I learned some things along the way that might be useful to others attempting this.
Firstly, land and brake to a standstill whilst still on the runway. Then watch for the spinning arrow at bottom right (which indicates MSFS is logging the landing against the achievement).
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If you see it then you can simply take off again (assuming you have enough runway!) and move on to the next airport. You do not need to exit the runway for this achievement to count.
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If you don’t see it then try turning around on the runway, going back towards the threshold and just before you reach it, brake. This seemed to trigger it for quite a few of my landings. However, after today I wondered if it could be related to the next issue I discovered - wind! (and not the kind caused by eating too many baked beans
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Landing when the headwind is above 20 kts sometimes (mostly!) caused the landing not to count. I think this is to do with the logic (if you could call it that!) which MSFS uses to determine if you have stopped. It seems to include the wind speed in the calculation! So if you are stationary on the runway after the landing and there is a 23 kts headwind MSFS says “you are still doing 23 kts so I am not going to count this as a landing”. Doing a 180 (previous point) sometimes corrected this but sometimes not. Today it was blowing a gale in the Shetlands, where I finished my trip and 50% of my landings didn’t trigger the spinning arrow, no matter what I did.
Sometimes the arrow wouldn’t appear until I had given up trying to force it and started my takeoff roll. It would randomly appear half way down the runway for some reason. Wierd!!
And then, randomly, no arrow would appear, despite greasing the landing and doing all the above 
It’s done now anyway. I only have Decathlon and Wing Commander left and then MSFS can nadger my Logbook any time it wants and I won’t care 