Preheat the air fryer to 375°F for 3 minutes.
Clean the crabs if they aren't already dressed: snip off the face just behind the eyes, lift the shell to remove the spongy gills on each side, squeeze out the bile sac, and trim the apron from the belly. Pat completely dry with paper towels.
Set up three shallow dishes: flour mixed with ½ teaspoon Old Bay, salt, and pepper in the first; beaten eggs and milk in the second; panko mixed with the remaining ½ tablespoon Old Bay in the third.
Bread the crabs: dredge each crab in the flour and shake off the excess. Dip in egg, letting drips fall back. Press firmly into the panko on both sides.
Load the basket: spray the air fryer basket with oil. Place crabs in a single layer, top-shell up, with space between each. Spray tops generously with oil.
Air fry at 375°F for 5 minutes. Flip carefully with a thin spatula, spray the second side, and cook 4-5 more minutes until deep golden brown.
Rest on a wire rack for 1 minute. Serve immediately with lemon wedges and tartar sauce.