yeah, not really any such thing as a safe failure mode. A slight bend is better than a shattering, but anything beyond a slight bend is going to hurt. I agree with the description above of Al failures. The main difference between steel and AL is that steel has a lot more tensile strength and Al has more of a fatigue life issue. No material is perfect. The important thing is, all material shortcomings can easily be made up for with proper design. There's a reason the tubing on AL bikes usually does not look exactly like the tubing on a steel bike, or a CF bike. Assuming you dont have a manufacturing defect or a design flaw, any frame material can be made into a bike that will last.