On the whiteboard at the flight school in working on my BFR it says "No flights dispatched over 99°". I've never seen this when I used to fly in the 2000's Is this an engine overheating concern or a density altitude concern? Is this common these days? The field elevation is ~800 but the runway is 5000'. I've flown there on hot days a long time ago and it didn't seem dangerous back then. Yes, a 3500 density alt is possible, but there are worse places out there.