From the pattern:

It gets cold up in the atmosphere, whether you’re in a
zeppelin or a biplane. To fend off the low air density chills,
knit yourself a cozy little aviator’s cap and keep those ears
warm. Despite the name, this cap’s not for aviatrices alone.
Intrepid male pilots should feel free to toss one on before
entering the wild blue yonder.

YARN Recycled from a wool/acrylic sweater; approximately 10 wpi or a light worsted. A good substitute would be 1 skein of Cascade 220 or 2 skeins of Elann Highland Wool.

SIZE One size; will fit a 21 to 25-inch head

NOTIONS One 1 3/8-inch shank button, one 3/4-inch button with two holes, darning needle, stitch markers