The Prospect trade union, which represents air traffic controllers, has hit back in the row over the plan to centralise air traffic control for seven Highlands and Islands airports - and its conclusions are supported by Comhairle nan Eilean Siar.
It means loss of air traffic control jobs at Benbecula, Orkney, Shetland, Stornoway, Wick and elsewhere. They would be replaced by a remote air traffic management system (RTS) supplemented by new IT.
An independent report by procurement expert Dave Watson commissioned by Prospect says implementation costs have already almost doubled. Safety and operational concerns have been raised over the proposed remote tower system. The report says the project will take at least £18m of economic benefit from island economies.
"In this case, the risks are not just financial; they are fundamental to the operation of airport services to the Highlands and Islands," it says. “Remote towers are not as yet proven technology in a setting as challenging as the Highlands and Islands.”
Proposals for a single remote tower centre were first mooted two years ago as part of Highlands and Islands Airports Ltd plans to "future-proof" its operations over the next ten to 15 years.
Commenting on the report, Councillor Uisdean Robertson, Chair of Transportation and Infrastructure at CnES, said: “This report confirms the arguments that the Comhairle and others have been making. This is a costly, risky, vanity project which should have been stopped long before now.
"The economic impact on island areas is unacceptable. The loss of jobs in the Islands is unacceptable. The risks are unacceptable. I repeat our call that HIAL think again about proceeding with these proposals and I would ask again that Scottish Government intervene.
"The report outlines that HIAL’s plans to relocate all air traffic controllers to a central location at Inverness, have underestimated the likely costs and risks of the project."
HIAL says remote towers are the “only option that offers long-term solutions in terms of resilience and flexibility”.
(This report has been updated with comments from CnES since first being published)