I remember pulling my hair out at this point as well!!
In this final chapter, did you search the skeleton when you first arrived on the platform with the aircraft? He's on the right hand side before entering the doors.
You will find some notes that will (should) help you get through these doors. I'm not sure though (sorry can't remember...) that THESE are the notes you will need, you might already have them in your inventory...
Anyway, you must use these notes that will give you clues to what door to open. You have to start with the S symbol and follow the order clockwise.