Plane crashes in mountainous territory (5)
I believe the answer is:
nepal
'mountainous territory' is the definition.
'Nepal' can be an answer for 'territory' (Nepal is an example). I am not certain of the 'mountainous' bit.
'plane crashes' is the wordplay.
'crashes' indicates an anagram.
'plane' with letters rearranged gives 'NEPAL'.
'in' is the link.
Can you help me to learn more?
(Other definitions for nepal that I've seen before include "Country located mainly in the Himalayas" , "Small lake" , "Asian country, capital Kathmandu" , "Asian kingdom" , "Mountainous country" .)