RISK & PROBABILITY

During audits and safety meetings I have often been asked ‘what are your top 5 risks?’ I have a problem with that question…

Let me start with a closer look at how the aviation industry historically quantifies ‘risk’. Once the system identifies a ‘hazard’ in the operating environment, we reach for a risk matrix of some kind – typically based on the 5 x 5 example described in ICAO Doc 9859, the Safety Management Manual. You know the one: ‘severity’ along one axis and ‘probability’ along the other.

I don’t really have a problem with the severity scale; it seems quite reasonable to imagine what the ‘worst case feasible outcome’ of the hazard could be and attach a severity in relation to the word pictures associated with the scale. But what about probability? Across the scale you will usually see 5 possible choices ranging from ‘very likely’ to ‘very unlikely’ or similar. What do they mean? If you look in the dictionary for ‘likely’ it will say something like ‘such as well might happen or be true; probable’ but that won’t mean a lot to a risk assessor. To help we tend to develop simpler word pictures to try and make the choice easier and more consistent or we might add a mathematical probability like ‘once in 10,000 flights’.

The trouble is that, once we have accepted that there is a probability of greater than zero, we need to be prepared for the outcome to happen at any time. Even if the probability is once in 10,000,000 flights, that accepts that it could occur on the next flight or the 10,000,000^th one, or anywhere in between. So for any activity that we propose to repeat indefinitely, like going flying, we must accept an inevitable occurrence whatever the probability.

Can I tell you what my ‘top 5’ risks are? No. While each of my identified hazards may have differing probabilities, they do have a probability and I don’t know which is going to happen next.