Originally Posted by
jimjim1
At present MAX seems to be about 65,000 and perhaps these balloons may sometimes be above that.
Last I heard from Airservices the letter of agreement with Google stated Loons would operate almost always above FL600 i.e. above CTA, and only descend below that under strict conditions, with notification to ATC.
It may be resolved now, but a couple of years ago the altitude information the Loons were generating via SSR and ADS-B wasn't pressure-altitude based. Instead it was height above terrain, based on the current GPS position referenced to an internal topographic database, which wasn't any use to ATC for separation.