Those seeking to understand the ultimate root cause of the debacle at Heathrow's Terminal 5 this week, might perhaps wish to consult British Airways' 'Baggage Handling Project Management Manual'. The key sentence can be found on p5:
The [project] process has a similar structure to the systems engineering principles used throughout industry.
Systems engineering is a top-down approach to large, complex engineering projects, which expends great time and effort in codifying and formalising the blindingly obvious, usually in the form of UML (Unified Modelling Language) diagrams.
The fundamental fallacy of Systems Engineering is the tacit belief that complex engineering systems are best managed by defining, often in very abstract terms, top-level requirements, capabilities and stakeholders, and by then breaking those top-level entities down into sub-requirements, sub-capabilities and sub-stakeholders, all considered in abstraction from specific technologies. Systems Engineering often requires systems houses to expend large amounts of time and money before crucial procurement decisions are made, and therefore constitutes a form of institutionalised procrastination. And, crucially, the top-down dogma has a tendency to produce systems lacking in practical operational effectiveness. True, practical, rapid and effective engineering uses both top-down and bottom-up approaches, in combination, and without any of the wasteful and vacuous formalising used by systems engineers.
Intellectually, Systems Engineering has never progressed beyond the facile observation that complex engineering systems are really 'systems of systems'. On Friday's edition of Newsnight, Allen Fairbairn, Systems Engineering Manager for the Channel Tunnel Project, offered the useful, and entirely non-specific diagnosis that large engineering systems often fail at the point where the various subsystems interact. This is the self-sustaining aspect to Systems Engineering: when it is responsible for the failure of a project, it provides generalised diagnoses of why the project failed, and prescribes more Systems Engineering as the solution.