Our office operated a GLEX in/out of there about 18 months ago. It is required that a Druk Air pilot, familiar with the airport, be on-board for the arrival. He was picked up in Mumbai, IIRC. VFR only, arrival is down a long valley, with the field unseen until about 1 mile final, hence the reason for the "navigator". Weights can be quite limiting, as you would expect. Jeppesen ITP has handled some trips thru there and should be able to assist. Crew stayed near the airport for several nights and toured around.
GF