Endlessly regret method securing new airport facility (6)
I believe the answer is:
runway
'airport facility' is the definition.
'endlessly regret method securing new' is the wordplay.
'endlessly' means to remove the last letter.
'regret' becomes 'rue' ('rue' can be a synonym of 'regret').
'method' becomes 'way' (I've seen this before).
'securing' indicates putting letters inside.
'new' becomes 'n'.
'rue' with its last letter taken away is 'ru'.
'ru'+'way'='ruway'
'ruway' going around 'n' is 'RUNWAY'.
(Other definitions for runway that I've seen before include "Strip for take off and landing of aircraft" , "A plane lands on it" , "Where one takes off" , "Strip on which planes take off and land" , "Airstrip" .)