Extensive tests on the plane's engine revealed the crack was a result of the "unique operating environment" of the test flight, and was not a widespread issue, he added.
The three-dimensional environment allows movement in any direction on foot, and the cockpit flight model allows you to roll and strafe in any direction.
The Natural Environment Research Council (NERC) has sent up a reconnaissance flight to investigate how the ash is distributed in the cloud, something that is impossible to assess from satellite imagery.