add folder to airplanes/747-400 folder

add following to aircraft.cfg

[fltsim.x]
title=Boeing 747-400 Trans World Airlines
sim=Boeing747-400
model=
panel=
sound=
texture=TWA
kb_checklists=Boeing747-400_check
kb_reference=Boeing747-400_ref
atc_id=BA747
atc_airline=BA
atc_flight_number=926
atc_heavy=1
ui_manufacturer="Boeing"
ui_type="747-400"
ui_variation="Trans World Airlines"
ui_typerole="Commercial Airliner"
ui_createdby="Microsoft Corporation"
description="TWA 747-400"