Over the years there have been aircraft accidents and incidents where crews have been found in error. Many times the errors were found with hindsight to have been compounded by poor checklists and inadequate design. Of particular concern to the author is the dilemma of ‘smoke and fire of unknown origin’. This is a serious emergency with little time for complex troubleshooting. It is a human factors classic ‘fight or flee’ scenario. Research among the major UK airlines, assisted by the UK Flight Safety Committee, has revealed that there is an inconsistency in direction as to when to recommend divert and land as of paramount importance. Thus a gap is created and those believed to be responsible identified. The author has experienced several instances and takes the opportunity to describe one of them. Lessons are included on work being done in modifying aircrew training to cater for the removal of the flight engineer. Design recommendations are made and warnings given about the future. Should recommendations in the wake of accidents and incidents be ‘risk managed’ by the regulators? Ultimately, the crews are forced to rely on their checklist handling and limited technical knowledge that sometimes means that the gap is too wide and an incident occurs. The paper is a collaborative effort prepared by the author on behalf of the RAeS Flight Operations Group (FOG) but the author alone is responsible for the version published.