LOGANAIR says the completion of large projects in Shetland like the gas plant and the new Anderson High School is one of the main reasons why its passenger numbers have dropped on flights to and from the isles.
Managing director Jonathan Hinkles told Wednesday's external transport forum that there was a "concerning trend" this summer which saw overall numbers on Shetland flights between April and August down by 5.2 per cent compared to the same period last year.
This is despite the average Shetland fare being 11.2 per cent lower than before, and seat capacity being up by 9.3 per cent.
There was a 10.7 per cent drop in passengers on the Aberdeen route, amounting to 3,818 people, while 2,020 less people used Sumburgh-Glasgow services.
Inverness was down by 11.9 per cent (785 customers) and Kirkwall was down three per cent (149 customers).
Bergen showed a zero per cent change from 2017 to 2018, while new direct summer flights to Manchester introduced this year were said to be performing well.
Edinburgh numbers were up by 7.6 per cent, but Loganair added more flights to the capital city to its schedule this year, increasing capacity by 33 per cent.
Hinkles said the number of flights from Shetland to Edinburgh have now been reduced from four to three because it wasn't economically viable.
He added that that some Saab 2000 airplanes have also been replaced on routes by smaller 340s.
Loganair also remained "consistently" in the top of five UK domestic airlines for punctuality, Hinkles added.
There was a number of flights affected in June, however, by a spate of thick fog.
Hinkles also said the cost of fuel prices have gone up, while carbon charges are also affecting all airlines.
South end councillor George Smith also questioned if Loganair would be changing its pricing policy, saying it can be "really expensive some times to make a last minute booking" or to change a ticket.
Hinkles admitted that it was a "balancing act", saying that if the airline did not make positive changes to its pricing structure after its battle with Flybe in 2017 then it would have seen a greater fall in its Aberdeen numbers.
But he felt the fare structure was "about as good as balanced" as it can be.
Smith said he thought it was always better to sell a seat than have it go empty - but Hinkles said during the "fare war" with Flybe there were plenty of empty seats even though tickets were cheaper.