As I've mentioned elsewhere I recently had quite a bad crash - broken collarbone, shoulderblade, and a rib. The circumstances are rather unusual: both brakes failed totally.
Crash details for those that want to know (TL;DR: I'd been using both heavily, let them off, they didn't come back on):
I was descending a mountain pass, as I often do, taking it rather slowly as the light was fading and the road was damp with some loose material. My habit when picking my way down that sort of road is to use the back brake lightly and continuously to control speed, and use the front brake for significant slowing before bends. Coming out of a bend I released both brakes as the next 100--200 m was straight and not too steep. When I was fast enough, I squeezed the brakes but carried on accelerating. I spent a few seconds trying to slow down, braking hard while rolling over the strip of grass up the middle of the road in the hopes of losing some speed, but knew I couldn't make the next bend, let alone the next few km of unbroken descent, so I headed for the grass off to one side to lose speed/hit something softer. I did manage to drop from around 35 km/h to more like 25 km/h but hit a rock with my front wheel and another with my body (and the aerobars with my helmet, hard enough to bend the aluminium armrest). Just before I crashed the brake started squealing, and the ceramic pads are normally silent.
The ride on Strava shows that only 20km earlier I'd had enough of a descent to put the brakes through their paces; at the top of the big descent I tightened the barrel adjusters and fixed pads a little as there was more slack than I would have liked -- and I tested them. A few days post crash the brakes stop the bike while it's being pushed, but the front wheel isn't rideable to test.
My bike has done about 16000 km and I recently had it serviced, including new brake pads. They're ceramic (I usually use metal), and normally have plenty of stopping power though I've had to tweak them a few times in the 1000 km since they were fitted -- new cables settling in? The brakes are Promax Render-R cable discs (BB5-style pads) and are normally good, barring one case of contamination.
I haven't taken the back wheel off but the front came off to get it home and I took the chance to inspect the pads:
(L) moving pad, (R) fixed pad.
The wear on the moving pad is strange. The pale patches are shiny metal backing and the actual pad is worn into a wedge shape. Update: I've measured the pad diameter, it comes in about 0.1 mm bigger than an old set of metal pads I had lying around, and the rotors are perfectly flat.
Further update: There are possible signs of melted material at the back, in the rotor air holes and the edges of the pad, and the pads turn out to be 70% ceramic (and 30% organic I assume). The front rotor has a groove worn into it to match the pads shown above, and has worn more in the month/~1000 km since these pads were fitted than in the previous 6 months since it was new. The rear rotor has also taken a lot of wear recently.
I'm as sure as I can be that I wasn't skidding the back - I was steering normally, not fishtailing. I didn't notice a different feeling in the levers, but I had bigger problems on my mind.
What could have happened? Could they really jam in the off position, perhaps due to heat? With one specific set of pads? I'm happy to replace the brake mechanisms when I can ride again, but want to understand the cause.