Experience has shown conclusively that the maintenance requirements will be different for each AGL system. The unique experience of TMS Photometrics in the operation and maintenance of AGL systems has resulted in the development of the MALMS Differential Maintenance strategy. The objective of MALMS Differential Maintenance is to enable an optimum maintenance strategy to be developed for each AGL installation. Normally this is based on the airport undertaking photometric measurement using the MALMS Mobile system and then targeting work identified only when and where required. TMS can assist this process by offering specially developed training courses. For example, an in-house training and seminar programme in Differential Maintenance, developed and delivered by TMS, is helping one major UK airport to radically refine its maintenance practices. Previously the airport was unable to maintain an acceptable level of performance without increasing its maintenance budget. Now, the changes in practice will ensure that acceptable performance is achieved at minimum cost.