Just tried to purchase some airship amenities while having the rank of 'Officer'. Button is greyed out and says I wouldn't have the permission to do so.
Not sure if Turbine only allows ranklevels 1-4 or 1-3 to buy that stuff, but I think the standard officier should have the permission to buy new airship amenities.
I was trying to buy that with my own money and not using the guild's plat/as. I also think every usual member should be able to buy such stuff if he thinks he wants to do so with his own plat/as.