Friday, 27 March 2015

Flight 4U 9525 and the dynamic Swiss cheese model

Swiss cheese model of accident causation
The Swiss cheese model
James Reason's Swiss cheese model explains how successive layers of defences can be breached, or weaknesses can line up, in order for an incident to occur.

The traditional depiction of the model is of a static succession of slices of cheese. In this model, closing one of the holes in the sequence prevents the incident.

A better way of visualising the concept is by thinking of a dynamic Swiss cheese model (see video). The weaknesses are not static and closing one weakness may cause another to open elsewhere in the same (or another) "slice".

Flight 4U 9525

The exact circumstances of the crash of the Germanwings Airbus 320 on the 24th of March 2015 have yet to be established. However it seems likely that the co-pilot intentionally flew the plane into the ground. The captain had probably left the flight deck to use the toilet and was then locked out of the cockpit by his first officer.

Post-9/11 cockpit doors

After the 9/11 terrorist attacks, cockpit doors were reinforced in order to prevent forced access. In terms of the Swiss cheese model, this weakness was therefore reduced. Crew could still access the cockpit if the pilot had become incapacitated by entering a keypad code. However, if the pilot was not incapacitated he or she could override the keypad system. Therefore a terrorist in possession of the code could still be prevented from getting into the cockpit.

The dynamic Swiss cheese model

The closing of the weakness in the structural/system layers allowing terrorists access to the cockpit opened a weakness in the set of circumstances where someone may want to access the cockpit for legitimate reasons against the flight crew's wishes. After the loss of Malaysia Airlines flight MH370, Popular Mechanics wrote a prescient article in March 2014 asking "Could Plane Cockpits Be Too Secure? Should pilots be allowed to lock themselves in the cockpit?" After the crash of Flight 4U 9525, in an attempt to close this new weakness, many airlines are now requiring the presence of two crew members on the flight deck at all times. It is unclear what new weaknesses this policy will create.

Lessons for the rest of us

Measures put in place in response to an incident will almost inevitably increase the risk of other, unforeseen incidents occurring. Time spent carrying out analyses and simulations of possible side-effects of the "fix" may allow us to minimise these new weaknesses.

Wednesday, 4 March 2015

Book of the Month: Being Mortal (Illness, Medicine and What Matters in the End) by Atul Gawande (Reviewed by Kirsten Walthall @K_Walthall)

About the author

Atul Gawande is a general and endocrine surgeon based at the the Brigham and Women’s Hospital in Boston, USA. Gawande is also a staff writer for The New Yorker magazine and the author of four best-selling books. His latest work, published in late 2014, is titled “Being Mortal: Illness, Medicine and What Matters in the End”.

Who should read this book?

Everyone – healthcare providers, patients and the lay public. Although several issues are highlighted through a case series of patients with medical problems, the book does not focus on the ins and outs of medical matters, such as the specifics of treatments. Gawande’s easy style of writing makes this book accessible to all. 

In summary

This book explores the concept of mortality and the impact that modern day medicine has had on it.
Using a series of cases, Gawande discusses the experiences of several people as they grow old, some with life-limiting diseases and others who simply become frail. He looks at the struggle to retain independence and autonomy; how care systems often try to provide support in a regimented way. Gawande discusses the concept of  “assisted living”, which helps people to continue to live the lives that they have lived. Furthermore, Gawande explores the belief of healthcare professionals that they have failed when a patient dies. Many find it difficult to accept that medicine cannot fix everything, and therefore may give poor information to their patients about what they realistically expect medical management to accomplish. Gawande discusses the importance of having those hard conversations with patients to find out what matters most to each individual so that therapy and care can be tailored to them. He argues that what we should be striving for is maintaining quality of life until death, rather than just prolonging life itself.

What’s good about this book?

Gawande uses #whatmattersmost on Twitter

The use of case studies and personal experiences to explore the issues involved in growing old and dying engage the reader. Gawande’s writing style makes “Being Mortal” very easy to read despite the potentially heavy subject matter. Mortality was not well covered in my undergraduate training – indeed it was barely touched upon – and I suspect that this is the same across the board in undergraduate medical education. This impression is supported by a study by Bowden et al (2013) who found that Foundation Year doctors expressed a lack of readiness to deliver end of life support and care.  “Being Mortal” really makes the reader think about the latter stages of life and the importance of preserving what matters most to each individual. It gives the reader an understanding of mortality that, for the healthcare professional, will benefit her patients and, for the individual, will benefit her, her relatives and her friends.

What’s bad about this book?

This is not a quick read book. It is very thought-provoking and encourages discussion - you will need time to read, absorb and think about its contents.

Final thoughts

This is by far the most inspirational and thought provoking book I have read – a must-read for anyone involved in patient care.


Bowden, J., Dempsey, K., Boyd. K., Fallon. M. and Murray. S.A. (2013) Are newly qualified doctors prepared to provide supportive and end-of-life care? A survey of Foundation Year 1 doctors and consultants, Journal of the Royal College of Physicians of Edinburgh. 43 pp.24-28 [Online] Available at: (Accessed: 02 March 2015)