Rex de Foor has posted a great question on the Ask a CFI forum where he noted that he has a student pilot who is doing well but his sticking point seems to his instrument scan. Rex noted:
I simply cannot get him to keep his instrument scan going. For a while he does well and then all of a sudden it is apparent he is losing the scan and becomes fixated. Any suggestions on how to break this bad habit?
Micah noted that he takes students through three phases of instrument training: 1) Basic attitude flying, 2) Basic navigation, and 3) Flying approaches. Once his students grasp the elements of each phase, he then moves on to the partial panel. After they become proficient at partial panel, he will then reintroduce the full panel. Micah noted that this will usually take some adjustment and then he will introduce the full panel in the next phase of learning.
Meanwhile, Steve Pomroy noted that fixation will tend to increase with fatigue. Hence, he suggested that Rex spend some time during the pre-flight phase making sure that his student is both well rested and fed.
However and if fatigue is not an issue, Steve added that plenty of practice will be required and it will take time. Moreover and in addition to backtracking the lessons a bit, Steve suggested that Rex should try having his student display his scan as they fly by actively pointing to the current instrument of choice. And while this approach may increase the workload, it will help to build up scanning capabilities.
If you are a student pilot, keeping the above suggestions in mind will go a long way towards improving your instrument scanning capabilities.
Just like driving a big rig or any vehicle, ground or air, fixation will tend to increase with fatigue. Being well rested and fed is the key to stop fatigue.