as deemed necessary (tlumach); as appropriate (Iv_lar); whenever required (Johnny Bravo); from time to time (YuliaO); at pace (Andrey250780); so far as necessary (Stas-Soleil); as it may apply (Technical); as may be requisite (elmajor); as the need required (Andrey Truhachev); on an ad hoc basis (We meet on an ad hoc basis Taras); as and when necessitated (Alexander Demidov); as may be required from time to time (AD Alexander Demidov); as the need arises (ABelonogov); as often as required (drag); as and when necessary (mascot); when necessary (Andrey Truhachev); when needed (Andrey Truhachev); on an occasional basis (Rori); as needed (Alex_Odeychuk)

as they are needed (Рихтер Дж. CLR via C#. Программирование на платформе Microsoft .NET Framework 4.5 на языке C#, 2013 Alex_Odeychuk)

as they see fit (Рихтер Дж. CLR via C#. Программирование на платформе Microsoft .NET Framework 4.5 на языке C#, 2013 Alex_Odeychuk)

ad hoc (not regular or planned, but happening only when necessary – We meet on an ad hoc basis. Kosarar)

as and when required (Alexander Matytsin)

as the circumstance arises (wikipedia.org Andrey Truhachev); in the circumstances (wikipedia.org Andrey Truhachev); pro re nata (об использовании препарата Dimpassy)

at the moment of need (напр., ресурсы выделяются процессу ssn); on demand (ssn)

по мере необходимости

: 35 phrases in 16 subjects

Automated equipment	2
Business	1
General	8
Information technology	2
Mass media	3
Medical	1
Nautical	4
Officialese	1
Oil / petroleum	1
Politics	1
Polygraphy	2
Programming	3
Quality control and standards	1
Space	1
Technology	3
Trade unions	1