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 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.
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.