Keeping the pilots in the air.
Something on the scale of operations, people doing it etc.
And their casualty rate and background vs. the pilots?
Air Power's Midwife ‒ Logistics Support for RFC Operations on the Western Front - P.J.Dye PhD thesis
The Bridge to Airpower - P.J.Dye - Book (pricey - how much overlap with his thesis?)
RFC Ground Trades
RFC mechanics images - Pinterest
RFC mechanics images - Google