Falling
Crashing
noun, verbal noun
If you crash and fall then you're crashing or falling, maybe both.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
あのジェット機の墜落は人為的ミスが原因だったと思う？
Do you think that jet crashed due to human error?