There used to be an agreed IATA loan rate of (IIRC) 1.5% of the component list price per day for the first 30 days. Add this to the initial loan fee of 2½% plus recertification by an approved shop when the unit is returned to the owner and you can see why some operators hate loans. If you have an agreement with another airline then often the mutual debts are wiped out at the end of each year.
In a previous life I dealt with Cyprus Airways who had been tied into a loan arrangement with Dan-Air. The air would be blue when an item loan would be billed at the cost (or more) to buy a second-hand overhauled part off the shelf from a BAC1-11 parts dealer!