Boeing is set to leave Druk Air's fleet replacement competition to Airbus and Embraer.
In a letter faxed to Druk on 9 October Boeing warned it was unlikely to meet the demonstration deadline after a deal to borrow the Malaysian government's Boeing Business Jet (based on the 737-700) fell through.
Druk wants two narrowbodies to replace two ageing BAe 146s as soon as possible, says Druk's general manager commercial Tandin Jamso.
In February an Airbus A319 became the largest aircraft ever to land at Paro Airport, which lies 7,300ft (2,230m) above sea level in a valley surrounded by 16,000ft-high Himalayan peaks. Druk accepts that Embraer is unable to demonstrate the 190 regional jet, as it has yet to enter production.
If new aircraft are added in the near future, as Druk wants, they are likely to be A319s, as only Airbus is in a position to deliver quickly.
While the board and government expect to have a proposal in their hands by early November, Jamso warns that cash and traffic concerns could cause the government to delay its decision until next year, strengthening the hands of Boeing and Embraer in the competition.