I was unaware that tiels are the fastest fliers of the Australian parrots. I read that statement somewhere today and I've been googling this and came up with many articles stating the same thing.
I can't say I'm too surprised because I'll boast every day what an awesome flier Lulu is - she is faster than Jerry and really a sight to see in flight. Here's a great little paragraph talking about tiels in flight:
"Their torpedo-shaped body and the long, slim, well-muscled wings help make cockatiels the fastest flyers of the Australian parrots. By far. Their descents would make them stars of any air show. Cockatiels plummet rapidly from on high in a perpendicular line not unlike a dropped stone. Then, only a few metres from solid earth, they spread their tails and wings, using them like the flaps on an airplane to soften their landing. Even generations of domesticity haven't diminished the flying ability of cockatiels."
Here's a link to the page where the excerpt above was taken - it has a wealth of all kinds of tiel information:
Pittwater Animal Hospital - Cockatiels
Lulu gives this information two wings up and a swan dive! 