Barometric Air Pressure Theory put to the test

One fine spring day, Kevin Pearce and I were completing the flight testing routine on my new Jabiru SK and all was going to plan. One of the tests was the VNE dive, the throttle was set as required and the aircraft descended from approximately 3000ft. We reached the required 116 knots, with quite a high rate of descent, made a note of the engine instrument readings and gently leveled off. A few seconds later there was a 'crack' sound. Neither of us spoke, there it was again - 'Crack'. No we hadn't imagined it! To top it all, as we discovered later, we had just flown through some smoke fumes emanating from the ground, so we thought, not only were the wings about to fall off but we were on fire as well! Emergency checks were carried out and a precautionary landing made at the airfield. A thorough check of the aircraft revealed no problems at all. Kevin mentioned the occurrence to Jamie, the Australian Jabiru test pilot with many hundreds of hours on Jabirus. He asked if we had had a plastic drinks bottle in the aircraft at the time - How did he know that! - Yes, I had a half bottle of spring water in a bag behind the seat. It turns out that he had had the same, almost loss of control of bodily functions, experience a couple of times himself due to pressure changes in expanding/contracting plastic drinks bottles! Normally you would probably get away with it but with the rapid height loss of the VNE dive and our increased awareness under flight test conditions……….!

Vic Leggott