Collocations for necessary - adj.

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

believe sth, consider sth, deem 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 the hospital for any longer than was strictly necessary.

absolutely
hardly
logically
medically

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

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

as necessary, when necessary, where necessary
We are here to give help and support when necessary.
Editorial changes have been made where necessary.

Necessary is used with these nouns:
adjustment, arrangement, attribute, balance, complement, component, compromise, condition, consequence, correction, degree, element, equipment, expenditure, expertise, facility, finance, impetus, improvement, information, ingredient, investment, level, majority, means, measure, modification, paper, paperwork, part, permission, permit, precaution, preliminary, prelude, preparation, prerequisite, procedure, qualification, reform, repair, requirement, resource, safeguard, skill, step, tool, training, truth