VERY FINE AND CHOICE MINT NEVER-HINGED EXAMPLE OF THE 1918 24-CENT AIR POST GROUNDED PLANE VARIETY.
The Grounded Plane stamps with pronounced vignette shifts are almost always found with hinged gum. This Mint N.H. example, with a significant vignette shift and from a better position, is very desirable.
Sanabria backstamp. With 1998 P.F. certificate