The heritage building has undergone a host of changes over the past year, including an upgrade of the observation deck and safety rail and replacement of exterior cladding.
Currently the group is waiting to see whether they will have more funding awarded to them to finish level two, which included a lot of work with windows.
"There were no windows on the outside, so they've been replaced and we had to check the vitrolite underneath. Fotunately, once it was cleaned up, it was all in pretty good order," Henderson said.
"We hope to have a decision on funding in June, after that the contractor will finish the work which will probably take about three months. We'll be looking to have an unveiling in October some time because the outside of the tower will be completed."
Opening in 1961, the Whanganui Airport Control Tower was the first of its type built in New Zealand. Many other towers throughout the country were modelled on it.
It no longer operates in a control tower capacity, but the funds are being sought to turn it into a museum and education centre.
The Airport Control Tower Restoration Group have been working to retain the tower and make it waterproof since 2004.
"It has taken that long, really, to raise the money to do it, the constraint has always been getting the money, but we know that it's waterproof," Henderson said.
"Now we can design what we need to make the interior right, it's all got to be lined, it will need new ceilings, new walls and new lighting, just to bring it up to standard."
Henderson hopes that the museum will be ready to open in two years' time.