The root cause of this accident was the failure of both the flight crew and the maintenance staff to fully consider why certain system abnormalities were indicated and what would be the consequential effects of the maintenance actions that were carried out. Flight crew, in particular, need to maintain a systems knowledge equivalent to that attained in the conversion course, in order to understand the potential for knock-on effects if systems are disabled or degraded by maintenance action. A few 'what if?' questions might have prevented this accident. The lack of lateral thinking left a big black hole, into which the flight crew fell under pressure of the abnormal circumstances. As I have previously posted, checklist discipline and a refusal to be hurried is of paramount importance in stressful abnormal circumstances, as this situation was.