Monitoring, the role of the non flying pilot, or the role of a single pilot, are an interesting and debatable issues.
The role and effectiveness of a human monitor will depend on how ‘monitoring’ is defined and what safety expectations exist.
Many people in the industry expect high quality monitoring from pilots; safety evidence suggest otherwise with accident and incident reports citing human error, blame and train. Why should we expect one pilot to understand a situation which the other might appear to have misjudged. Both are human who may have different situational understandings; however, where each is sufficiently close forming a shared ‘mental model’, then there is no need for intervention. Yet where awareness differs to the extent of requiring intervention, which view is correct; who judges, on what basis. This suggest that the concept of monitoring flawed.
Compare this with dual tech systems requiring a ‘comparator’ alert, and need for an alternative third system for judgement, yet even that has weaknesses when considering multiple failures.
What happens when both pilots awareness is incorrect, good shared mental model, but wrong; typical of illusionary situations, both visual, and mental constructs.
Does the industry assume that the PM is always correct, yet they may be the less experienced in forming awareness. So should the more experienced be the PM monitoring, which might imply that the less experienced will fly the aircraft.
The design of a modern high-tech aircraft should not consider pilot monitoring of automation (a warning or caution for critical failures), systems alone are less error prone than the human, yet the human is a very valuable monitor for the overall situation, the resultant of human-system interaction and the operating environment (do we think or train for that view). The autos a working correctly but the output is not what the PF intended.
Some aspects of these may be suitable for automatic monitoring; system inputs can be bounded avoiding unsound inputs (flight path protection, FMS data entry), and at a lesser level, cautions questioning intent (selecting low autobrake on a contaminated runway), but even this requires knowledge of the situation which only the pilot may have.
There is not a win-win situation, only a balance; and perhaps that balance is moving more towards automation partly because of mistaken beliefs that early automation reduces training and experience for understanding systems, greater efficiency, lower cost. However recent developments in automation are closing this gap; safer automatic flight with less training, but IF and only IF the operating environment does not expect even more savings and efficiency.
Many of today’s safety issues are within this ‘IF’ proviso (complexity, workload, fatigue), thus without reappraisal of these goals, then single pilot - automatic operations might be no safer than today (but is that good enough). Also in changing to a single pilot the industry risks introducing some other, unforeseen safety issue.
Who monitors the regulators or operators; what is the basis of their risk management training with respect to actual operations.