Concorde Alpha Foxtrot has sat on the tarmac at Filton since 2003
Campaigners have called for an investigation into the future of the Bristol Concorde visitor attraction.
The retired plane, based at Filton airfield, will shut in October when Alpha Foxtrot is moved into a hangar for maintenance work.
The jet was the last to be built in Filton and the last of the fleet to fly when Concorde was withdrawn from service in 2003.
Airbus UK, who look after the plane at its base in South Gloucestershire, will not say how long the work will take.
Oliver Dearden, of the Bristol Aero Collection, which manages public tours for Airbus, told BBC Bristol he did not know "whether we have to close down".
Now the Save Concorde Group fears the attraction may never return and wants an inquiry into what is going on.
Built at Filton near Bristol
Maiden flight was 20 April 1979 before being delivered to BA in 1980
In 1989, was the first Concorde to suffer 'rudder superation' where part of the rudder was lost in mid-flight
In 1993, was fitted out with leather seats
Its final flight was from Heathrow to Filton on 26 November 2003
It was the final ever flight of a Concorde
The group's vice-chairman, Ben Lord, told BBC Bristol the mystery surrounding the maintenance was a cause for concern.
"What we don't quite understand is why the plane has to undergo this maintenance inside a hangar when it has managed to stand open and exposed to the elements for the previous six winters.
"It brings about an element of intrigue as to why this is being conducted.
"Airbus UK are remaining so very tight-lipped on this to all concerned that we simply don't know what they're intending to do.
"We simply don't know as long as Airbus continue not to be open and honest about what's really going on."
Airbus carries out weekly maintenance on Alpha Foxtrot each Monday but could not confirm the reasons for moving the jet into a hangar for further work.
"It is being closed in the autumn for maintenance and inspection which is required as part of the contract," the Airbus spokesperson said.
"There is no opening date as we have to see what maintenance needs to be done - until we know we can't give any certainty."
Mr Lord said there could be two extreme possibilities over the maintenance - and fears one may be a reaction to his group's involvement in an attempt to get a Concorde flying again.
"Either it's an attempt to take Concorde out of the public eye in Bristol - which would be totally deplorable.
"Or, on the other hand, it is a reaction to our hard campaigning which has taken place since Concorde's retirement [to potentially bring] her back into a flight-worthy condition for the 2012 London Olympics opening ceremony."
Save Concorde's vice-chairman said he has now contacted Concorde's owners in a bid to get answers.
"I have written to British Airways, who own the aircraft, to find out what they feel about this because it is an asset that they still own and they very much need to be in the know as to what's going on.
"At the moment their reaction is that they are leaving this to Airbus to do whatever they see fit in this maintenance routine that's taking place - which also seems to me to be quite strange."
British Airways was unable to shed any light on the situation.
A spokesman told BBC Bristol: "We visit all eight Concordes each year to do an audit of the maintenance that has taken place on our aircraft.
"But the maintenance schedule itself is a matter for Airbus, as is the question of when the public is given access to the aircraft."