It's a trial, we'll look at the results over the next few days and take a view. I agree that they are fairly intrusive at the moment, but the whole publishing business model has changed significantly over the years and we have to look at all potential revenue streams (we decided not to go for the click bait stories you get running along the bottom of many websites).
I don't envy that problem. I'm 3 years out of the online advertising game, which is probably = forever given the speed that evolves at, but my thoughts would be:
1) Instinctively I'd expect adverts at the end of a thread to get a better CTR than in the middle of the thread.
2) Stuff between posts should be bespoke placements for targeted brand awareness campaigns, rather than miscellaneous stuff seeking a click-through. Alternatively, 'wrap around' sponsorships work well for driving brand awareness, and whilst visually impactful, don't really impede the user experience
3) I'd be surprised if stuff like Google Adsense will work well on a specialist forum. Posts are too transient and we write too much jargon for Adsense to work out what they're about. Whilst a forum discussing hi-fi is likely to attract adverts for hi-fis .... I'm not sure there are enough Electronic Conspicuity advertisers on google for a thread discussing EC to attract targeted adverts.
4) If you don't do it already, tagging the ATIS pages with real world placenames would probably help Adsense serve relevant stuff to those looking at destinations. e.g. Google maps isn't sure where 'Fairoaks' is, so Adsense will be having the same problem. Tag it with Woking and you might gets ads for hotels in Woking. My instinct if I was going to monetise the traffic to the forum would be to grow the ATIS section into a proper airfields database - there's a wealth of knowledge to be contributed, and it would be genuinely valuable
5) I'm surprised the forum isn't used to promote the magazine more - or is the assumption that we're all already subscribers?
6) Similarly, I'm surprised the forum isn't used to complement the magazine more - e.g. if I advertise a share for sale in the magazine, getting a few 1,000 impressions of the same advert on the forum would make that advert a lot more valuable.
I realise it's probably not that simple, but my instincts are there a lot of ways to monetise the forum, and basic network advertising isn't high up my list.