Collocations for necessary - adj.

be, prove, seem | become | remain | make sth
The cold weather has made it necessary to protect the crops.

consider sth, feel sth, find sth, regard sth as, see sth as, think sth
Make any alterations you consider necessary. | You may find it necessary to readjust the wheels from time to time.

really, strictly
I was determined not to stay in hospital for any longer than was strictly necessary.

absolutely | causally, logically

for
qualifications which are necessary for work with the under-fives

if necessary
These measures will be enforced, if necessary, by the army.

as/when/where necessary
We are here to give help and support when necessary.