The first two UA loading zones on this level occur in the first half of the map, before the engine is blown. The first comes just after the broken door, soon after you drop into the ship proper (the door bursts open after you deal with your first batch of Sentinels). The Green Arrow shows the location from which you came. Just past this zone is the Cafeteria.
Watch the movie for Maw Zone #1
Once you've passed the cryo control chamber (and its mass of Flood and sentinels), you'll come to a maintenance hatchway again. The second loading zone is in the maintenance hallway past this point.
Watch the movie for Maw Zone #2
The third zone on the Maw actually occurs during the final run; it's before you get to the meeting place with Foe Hammer, and your distance readout will be 734m (the zone itself is roughly 1m wide).
Watch the movie for Maw Zone #3