I stand corrected…
LHTR 1.3 under “Step 7: Press Attack or Retreat”
When you designate that an air unit will retreat, return it to the game board battle site. It will retreat as a noncombat move when all other air units finish their moves in the noncombat move phase. Air units can retreat to any friendly territory within their total movement range. A fighter can retreat to a friendly aircraft carrier or to a friendly sea zone, as long as a carrier moves there this turn.