Maybe of interest to this intriguing project in PNG: The use of a magnetometer in the search for VH-MDX in the Barrington Tops was research recently. This involved opinions from those who use these devices commercially as part of mineral exploration. It was concluded that the target was too small to be able to get close enough (estimated at 20m) from the air to detect the very small amount of ferrous metal that would be in a small aircraft wreckage in a rainforest.
If you can make a magnetometer of use in this type of search I’d love to hear about it.