Holism: next step in the evolution of structural airworthiness?

Many say we should manage our health ‘holistically’, that we should always look after our whole being and not just wait to treat individual diseases. Could ‘holism’ also be good for structural airworthiness?

In February 2019, as snow blanketed the USA, twenty aeronautical engineers were meeting (as they do every year) to discuss that very question. I was one. (Yes, that’s me presenting in the photo above.) On our minds was a recent fatal accident in the USA. Fatigue and corrosion had unexpectedly and dangerously interacted to break a blade off the propeller of a Lockheed KC-130T Hercules transport. It set off a chain of events that broke up the whole airframe in flight. The aircraft crashed in pieces, killing all on board.

Dr Hoeppner

For the meeting’s leader, Dr Hoeppner, Emeritus Professor at the University of Utah, it was another tragic reminder of why he first proposed his Holistic Structural Integrity Process (HOLSIP): to manage structural risks from all foreseeable hazards, not just those the standards prescribe; to consider how hazards interact, not just in isolation; to understand the true nature of materials, not just their engineering ideals; to understand the physics of structural degradation, not just the test results; and to analyse structure more like a system, including reliability. Dr Hoeppner is internationally renowned for his pioneering work on the structural airworthiness of engines as well as aircraft.

Could HOLSIP be the next step in the evolution of structural airworthiness, after ‘safe life’, ‘fail-safe’ and ‘damage tolerance’? The last is still a sound concept, as Bob Eastin and I told ICAF in 2005 (see our paper, ‘Rough Diamond’, on my ‘Tech’ page), but HOLSIP could improve its application. HOLSIP is like a Safety Management System (SMS) for structure.

For a more complete description of HOLSIP, see this page on the HOLSIP website.

My presentation to this year’s Workshop was, ‘Holistic Standards for Holistic Projects, like ERSI’. ‘ERSI’ is short for ‘Engineered Residual Stress Implementation’, a project by which the USAF hopes to safely reap more benefit from intentional residual stresses such as introduced by ‘cold expanding’ fastener holes. An important project deliverable will be new regulatory guidance for MIL-STD-1530D and JSSG-2006. Dr Michael Gorelik, the US FAA’s Chief Scientific and Technical Adviser for Fatigue and Damage Tolerance, is also involved for civil aviation.

My presentation is available on my ‘Tech’ page. Also see my posts on previous HOLSIP Workshops.

I greatly respect Dr Hoeppner and others pursuing a more holistic approach to structural integrity, and hope to continue to attend the HOLSIP Workshops in the USA.