Ehh? this is interesting

[Azred]

Molybedenum is definitely used in aircraft manufacture; most modern ultra-strength metals use Molybedenum (symbol: Mo) as part of the alloy. Although this metal does increase the strength of alloyed steel at higher temperatures, it will oxidize at a sufficiently high temperature, even in the absence of oxygen. It has many of the same general chemical characteristics as chromium and tungsten.
Magnesium is also used in aircraft construction; when alloyed with aluminum it increases the welding properties of the aluminum. Unfortunately, at higher temperatures the magnesium will still ignite and cannot be exinguished with water (elemental Mg reacts with water).

@Buttercup: thank you for the most reasonable explanation for the sand/gravel I've heard yet.

@Tancred: I don't recall that any flight data has been released publicly yet. A news search should produce some answers.