Isn't there some way you could use two separate gases, which in their
separate state are inert, but combined together under high pressure,
become
explosive? Such a combination would not ignite if the airplane crashed
(you could separate the gases into separate containers on each side of the
airplane, at the wingtips), but in controlled injection into a high
pressure
compartment could be made explosive in a controlled way, in a very limited
space.

We've been using this for years in spacecraft. The Titan II that launched
Gemini capsules was powered by hypergolics. Mainly, though, these fuels are
used for in-orbit engines (Apollo, Soyuz, space shuttle, and Shenzhou all
use hypergolic propellants). The most common ones used are unsymmetrical
dimethyl hydrazine (UDMH) and nitrogen tetraoxide (NO4). These two
chemicals are EXTREMELY toxic.

Also, the Russian Proton rocket, and the launch vehicle the Chinese used to
launch their taikonaut, are powered by hypergolic fuels.