Flights from London in planes appear dubious for vacation, unfortunately (6,3,5)
I believe the answer is:
apples and pears
'flights from london' is the definition.
The definition suggests a plural noun which matches the answer.
'planes appear dubious for vacation unfortunately' is the wordplay.
I cannot quite understand how this works, but
an anagram of 'planes' is 'plesan' which is present in the answer.
This explanation may well be incorrect...
'in' is the link.
Can you help me to learn more?
(Other definitions for apples and pears that I've seen before include "Selection of fruit" , "Steps" , "taken by healthy eaters?" , "London flight" , "stairs in east London" .)