Cut and paste what's below into your AIRCRAFT.CFG file, change fltsim.x to be flitsim.{the next number above the highest number used in the existing entries}

[fltsim.x]
title=Boeing 737-400 Thai Airways
sim=Boeing737-400
model=
panel=
sound=
texture=thai
kb_checklists=Boeing737-400_check
kb_reference=Boeing737-400_ref
atc_id=HS-TDJ
atc_airline=Thai
atc_flight_number=TG001
ui_manufacturer=Boeing
ui_type=737-400
ui_variation=Thai Airways
description=Thai Airways operates B737-400's on it's domestic routes throughout Thailand from it's main hub located in Bangkok.\nTed Thompson/Federal Productions\nEmail: info@federalproductions.com