Anne,

The single most important factor in selecting a design firm is the ability
of those making the selection.  Those who make the decisions are often
uninformed, unaware, and  unqualified in making the basic decisions of
what design and designers can do with their precious MONEY.

Most people that are new to museums think of exhibit design as "displays"
which they have seen in store windows at the "mall", trade shows, Las
Vegas and Disney World, which brings up the issue of the "Exhibit
Designers and Producers Association".  A fine organization, which I am a
member, but it is dedicated more to the design/production aspect of
exhibits.  It is not the same as the other group which I am also a member,
the "American Association of Museums" a group dedicated to the furthering
of excellence in all facets of museum conception, development, and
continuance.

Regarding the cited much needed past experience of design firms which have
done work for a "niche" museum such as an aviation museum narrowed down to
W.W.II, why not limit it even further to a museum of aviation dedicated to
 those pilots of Polish/Italian descent whose grandmothers were married in
Krakow on August 21, 1904, moved to Pennsylvania in the spring of 1912,
and, after moving to Chicago in the winter of 1930 bought a used low
mileage 1928 Essex two door sedan?  There are probably three to four
hundred design firms that have such a museum in their portfolios anxious
to do still another museum of such importance--- a hard decision to make,
so many slides to see and RFP's to read and ignore.

My advise is to join one of the above mentioned organizations, and read,
read, read some of their publications before making any basic decisions.