A bucket curve is one whose slope initially decreases at a high rate, then follows a plateau, then rises steeply again. Like a 'U' with a flattened bottom.
If maintenance cost is expressed on the Y-axis and time on the X-axis, you have a situation where initial cost might be high due to delivery snags, bedding-in issues etc, but then it ramps down to an on-going low level before rising again as parts wear out, corrosion takes hold and critical items become scarce.
Ryanair is fortunate enough to be on the flat bit - just regular maintenance costs to meet. Whereas HM's ancient beasts are mostly climbing up the right hand side of the curve, being long past their 'Best before' dates.
TT:
However, the more I think about it, the more I suspect that being a civvy reservist in the military role will probably be the worst of both worlds, not the best of both.
You may well be right. We tend to remember the better times - and how the service was 'back in our day'. Much will have changed since then; whether for good or bad may not be immediately obvious.
By the way, don't forget that the 'Gp Capt' will also end up with a nice pension - I hope that you're able to salt away some of your new-found wealth for your latter years.