carbon brake testing
Reading the Boeing web-site on the progress of certification for the 777-300ER I was interested to read that the Vmbe tests are carried out with the pads sanded down to replacement time values. But these are carbon brakes and I thought that carbon brakes should also be replaced if plastic deformation had occurred to the extent that normal braking would not remove any glazed matrix buildup. Carbon brakes work better than steel when hotter but too hot and they put on a coat like ceramics. Sanding down merely replicates low energy braking wear, exacerbates heat generation on subsequent high energy braking and the thinness limits heat rejection therefore risking tyre deflation. So the sanded down pad test only tells you how dangerous thin sanded pads are but not how dangerous partly worn, outwardly normal brakes are. Okay you either provoke or resist a braking failure in the test and a tick may or may not go in the test-sheet. But as a test of the true failure mechanism in normal use of a material still not fully understood [well it may be understood but the manufacturers are a tad shy of explaining it] it is surely as practical as a chocolate teapot. Some day someone who thinks he is doing everything right and by the book is going to run out of road and end up in the kitty litter. Thoughts?