6.1 General Tournament Scenario

Q: Since a landed transport aircraft is a 0cm move War Engine, is it possible to garrison a loaded one, such as a Marine Landing Craft or Ork Landa?
A: No. 4.2 specifically states that aircraft must start off-board.

4.2 AIRCRAFT
Aircraft formations are not set-up with other units. They are kept
off table (where it can be imagined they are in orbit or stationed
at a nearby airbase) but can be set up on the board when they
take an action. Aircraft that are capable of transporting other
units may be set up with the these units already on board. The
aircraft (plus any units they are transporting) may only enter play
using the following rules.