Is the Airport Sensible?

I've been surfing the web, as you do, and discovered that a civilian version of the Chinook Helicopter has an extended range of 1400 miles and a normal range of 450 miles. At a cruising speed of 150mph it could relatively easily fly from Ascension to St Helena in 5 hours, refuel and fly back the next day. I'm sure Ascension could service a Chinook (it is an American base) so all that would be needed on St Helena is a Helipad and fuel - sounds a lot cheaper than a giant runway... Especially as I understand a chinook can essentially land on anything so all it really needs is fuel and a shed for Customs and Immigration to wait in...

I also note that a Chinook can carry 55 people (it may end up less with the increased fuel load) - well that seems to be the going numbers for the RMS trips to Ascension so sounds about right, but operating once or twice a week rather than once or twice a month would  bring the tourists in. All that would be needed is to cut the red tape about who can land at Ascension...

I therefore assume that diplomatic relations with the Americans are so poor that we cannot negotiate additional civilian passengers passing through Ascension (it is a British Dependency - although possibly you wouldn't believe it) or there is another reason for building an Airport on St Helena. Or have they just not realised that you can fly a helicopter 700 miles if you put your mind to it. Or perhaps Helicopters are significantly more expensive to run than planes - even allowing for the cost of building an Airport.

I don't know,  but struck me as strange that I haven't even heard it being considered.