Why this answer
The verdict comes from all three measured axes.
Fjallraven Raven 28 is over the published personal-item dimensions, but the soft construction may make it a borderline option if lightly packed. Treat this as a fee-risk result.
The selected rule is 18 x 14 x 8 in and the bag record is 18.5 x 12.2 x 8.3 in.