Sounds really unlikely, at least the SFO numbers... maybe in Luton on a busy month, but in CEE expect net closer to €36k yearly average (so €3k/month). €4k net in one month is possible with 100hrs, maybe some combination of flying on your OFF days, out of base, random roster etc. (my record is €3,5k)
This is however based on normal local employment contract, single household taxation, full social security etc. - maybe if you were on agency contract and got "creative" with taxation you could do better.