This is my own theory, it doesn't apply to the real thing seen on the sightings.
The TR-3B is a stealth equilateral triangle shaped blimp, it is filled with lighter than air gas to float and slow down descent thus eliminating the need for more powerful engines. The afterburners at each tip are used to maneuver the craft like a tricopter.
(I suck at making descriptions)

How to take off

Turn on AG1 then retract the landing gear.

Activation Groups

AG1 - Activate the whole thing

AG2 - Landing lights

Controls

Pitch - forward and backwards

Roll - steering

Yaw - left and right

VTOL - up and down

How to land

Find a landing spot, put down VTOL and pull out landing gear, once you touch down on the surface turn off AG1.

Google maps and Picsart used to make thumbnail