It is not a matter of what is on the bank statement. It is more a matter of what is not on the bank statement. The term bank statement being used loosely, so include within it credit card accounts.
Naturally any dodgy transaction involves the use of cash, readies. Necessitated by the need for not wishing to a subscription to tax, subscribing to benefits, avoiding debt, involvement in drugs, fraud, terrorism and any other form of foul play you can think of.
But when it comes to flying, most unlikely that the ostrich who is up to no good will be able to resist to clock the flying hours in his log book. So if the entry is in there and the source of payment /cost for it is nowhere to be seen, then what is the story. Better be a convincing one. Conversely if the ostrich thinks he is an owl, then he will resist the temptation and not book the hours. But then he will be taking another risk that maybe someday someone will question why his name was down on some airfield or airport and yet not down in his log book. For which I suppose many a excuse may be put forward. However if it was in real-time electronic form, just as HMRC have all employers do their payroll, then there will be little room to invent an excuse.