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Delaforge

It may be better to examine this from the point of view of mundane astrology as some event chart. Certainly people are free to cast horaries for whatever they wish, but typically casting a horary for something which is personally meaningful or which weighs upon your mind/soul is where horary really comes to life.
"The only true wisdom is in knowing you know nothing" - Socrates

https://heavenlysphere.com/

4
Even if you do not have a relative or friend on the airplane you can ask the question. The only requirement is that you have a an *interest* that is intense or meaningful enough. No one can judge that, only you, (the querent) can know.

I have accurately judged dozens of horaries about people the querent has no direct relation to. It is the intensity of the interest that matters. You can see some on medical matters on my web site.

To answer your question: the significator of such an airplane is the ruler of house 7. If house 1 is "the ship I/we sail in", house 7 is the ship that those "general people" sail in: house 7.

See what house 7 and its ruler are up to and you get the answer. An accident will have house 6 and/or its ruler active. Terrorism will have the turned house 7 (open enemies) and/or house 12 (hidden enemy/hidden attack) active. Pilot suicide will have the turned house 12 active (self-destruction). And so on...

If your question is about the welfare of a relative or a friend then the question is not about the plane. In that case use the house corresponding to the person. If the question is about what caused the plane to come down then ask about the plane: house 7.
--
Felipe Oliveira
http://traditionalmedicalastrology.org
http://medicalastrologer.net