AIR FORTRESS (O is the letter)
 
First Quest:
Stage 2: I8TA
      3: KA9I
      4: 6KAI
      5: 8NYU
      6: 2APP
      7: OS85
      8: SUGA
Second Quest:
Stage 2: 11NA
      3: 5AJI
      4: TOBI
      5: NDA4
      6: MA1K
      7: DOMO
      8: 7NDE