When the evidence needed to reconstruct an aviation accident is lost or destroyed in the crash, can the victim nonetheless hold whoever caused the accident accountable?

Yes, if the legal doctrine of "res ipsa loquitur" apples — Latin for "the thing speaks for itself."

Most courts recognize that air crashes do not normally occur unless someone, somewhere, was negligent.  It’s just a matter of who.  If circumstances point to one particular person above all others, then "the thing speaks for itself," and that person can be held accountabe even without any physical evidence to prove the case.

Let’s say an airplane’s engine fails and the plane crashes. The pilot survives but is badly injured. The key engine components are either battered beyond recognition, destroyed by the post-crash fire, or never located. Under the circumstances, it may be impossible to ever determine exactly why the engine failed.  There may be little chance of determining from the wreckage who was responsible for the accident.

Now assume that engine work had been performed on the plane just before the accident. Under the circumstances, one might suspect that the engine failed because the mechanic who performed the engine work did something wrong.  Of course, there are other possible explanations for the engine failure as well.  But if the injured pilot can prove that the mechanic’s work is the most likely explanation, a judge or jury may decide that the maintenance shop is responsible, even without any physical evidence to rely on.

To invoke the doctrine of res ipsa loquitur against the maintenance shop in this example, the injured pilot must prove that:

  1. The engine would not have failed unless someone was negligent;
  2. The maintenance facility had exclusive control of the engine during the key time period (that is, only the facility’s own mechanics had access to the inside of the engine when it was opened up); and
  3. The pilot did not cause or contribute to the engine failure (by, for example, running out of gas).

Even if there isn’t enough physical evidence to determine how or why the engine failed, if the pilot can prove all these three things, he may nonetheless be able to hold the shop responsible for his injuries.