Reply #37: 'Virtually indestrucible' - Hardly

[KDLarsen]

They're designed to withstand a plane crash. Here's the current specs:

Meets the following requirements:
ARINC 747 - TSO C124 - EUROCAE ED 55
- Resistance to shocks: up to 3400 g, for 6 milli sec.
- Resistance to penetration: an impact of 225 kg falling from height of 3 meters
- Resistance to static crush force: 5000 pounds, for 5 min, on all axis
- Fire test: 1100°C flames for 30 min, on entire surface
- Fire test: 260°C - 10 hours
- Resistance to immersion in aircraft fluids: 48 hours
- Resistance to immersion in seawater: 30 days at depth of 6000 m

http://www.sagemavionics.com/ProdFiles/Brochures/FlightDataManagement/SSFDR.pdf

Which is what you'd expect to happen in an airplane crash. They certainly don't build them to withstand crashing into a building, then having said building fall on top of it, and then the rubble being on fire for quite a long time.