Simply put, it is possible to have convenience if you want to tolerate insecurity, but if you want security, you must be prepared for inconvenience.

Gen. Benjamin Chidlaw (1954)

It is highly questionable whether total system safety is always enhanced by allocating functions to automatic devices rather than human operators, and there is some reason to believe that flight-deck automation may have already passed its optimum point.

Earl Wiener (1980)

If you want to know where Crew Resource Management as a discipline started, then you need to read NASA Technical Memorandum 78482 or “A Simulator Study of the Interaction of Pilot Workload With Errors, Vigilance, and Decisions” by H.P. Ruffel Smith, the British borne physician and pilot. Before this study it was hours in the seat and line seniority that mattered when things went to hell. After it the aviation industry started to realise that crews rose or fell on the basis of how well they worked together, and that a good captain got the best out of his team. Today whether crews get it right, as they did on QF72, or terribly wrong, as they did on AF447, the lens that we view their performance through has been irrevocably shaped by the work of Russel Smith. From little seeds great oaks grow indeed.

When you look at the safety performance of industries which have a consistent focus on safety as part of the social permit, nuclear or aviation are the canonical examples, you see that over time increases in safety tend to plateau out. This looks like some form of a learning curve, but what’s the mechanism, or mechanisms that actually drives this process? I believe there are two factors at play here, firstly the increasing marginal cost of improvement and secondly the problem of learning from events that we are trying to prevent.

Increasing marginal cost is simply an economist’s way of stating that it will cost more to achieve that next increment in performance. For example, airbags are more expensive than seat-belts by roughly an order of magnitude (based on replacement costs) however airbags only deliver 8% reduced mortality when used in conjunction with seat belts, see Crandall (2001). As a result the next increment in safety takes longer and costs more (1).

The learning factor is in someways like an informational version of the marginal cost rule. As we reduce accident rates accidents become rarer. Now one of the traditional ways in which safety improvements occur is through studying accidents when they occur and then to eliminate or mitigate identified causal factors. Obviously as the accident rate decreases this likewise the opportunity for improvement also decreases. When accidents do occur we have a further problem because (definitionally) the cause of the accident will comprise a highly unlikely combination of factors that are needed to defeat the existing safety measures. Corrective actions for such rare combination of events therefore are highly specific to that event’s context and conversely will have far less universal applicability.  For example the lessons of metal fatigue learned from the Comet airliner disaster has had universal applicability to all aircraft designs ever since. But the QF-72 automation upset off Learmouth? Well those lessons, relating to the specific fault tolerance architecture of the A330, are much harder to generalise and therefore have less epistemic strength.

In summary not only does it cost more with each increasing increment of safety but our opportunity to learn through accidents is steadily reduced as their arrival rate and individual epistemic value (2) reduce.


1. In some circumstances we may also introduce other risks, see for example the death and severe injury caused to small children from air bag deployments.

2. In a Popperian sense.


1. Crandall, C.S., Olson, L.M.,  P. Sklar, D.P., Mortality Reduction with Air Bag and Seat Belt Use in Head-on Passenger Car Collisions, American Journal of Epidemiology, Volume 153, Issue 3, 1 February 2001, Pages 219–224,

AI winter

Update to the MH-370 hidden lesson post just published, in which I go into a little more detail on what I think could be done to prevent another such tragedy.

Piece of wing found on La Réunion Island, is that could be flap of #MH370 ? Credit: reunion 1ere

The search for MH370 will end next tuesday with the question of it’s fate no closer to resolution. There is perhaps one lesson that we can glean from this mystery, and that is that when we have a two man crew behind a terrorist proof door there is a real possibility that disaster is check-riding the flight. As Kenedi et al. note in a 2016 study five of the six recorded murder-suicide events by pilots of commercial airliners occurred after they were left alone in the cockpit, in the case of both the Germanwings 9525 or LAM 470  this was enabled by one of the crew being able to lock the other out of the cockpit. So while we don’t know exactly what happened onboard MH370 we do know that the aircraft was flown deliberately to some point in the Indian ocean, and on the balance of the probabilities that was done by one of the crew with the other crew member unable to intervene, probably because they were dead.

As I’ve written before the combination of small crew sizes to reduce costs, and a secure cockpit to reduce hijacking risk increases the probability of one crew member being able to successfully disable the other and then doing exactly whatever they like. Thus the increased hijacking security measured act as a perverse incentive for pilot murder-suicides may over the long run turn out to kill more people than the risk of terrorism (1). Or to put it more brutally murder and suicide are much more likely to be successful with small crew sizes so these scenarios, however dark they may be, need to be guarded against in an effective fashion (2).

One way to guard against such common mode failures of the human is to implement diverse redundancy in the form of a cognitive agent whose intelligence is based on vastly different principles to our affect driven processing, with a sufficient grasp of the theory of mind and the subtleties of human psychology and group dynamics to be able to make usefully accurate predictions of what the crew will do next. With that insight goes the requirement for autonomy in vetoing of illogical and patently hazardous crew actions, e.g ”I’m sorry Captain but I’m afraid I can’t let you reduce the cabin air pressure to hazardous levels”. The really difficult problem is of course building something sophisticated enough to understand ‘hinky’ behaviour and then intervene. There are however other scenario’s where some form of lesser AI would be of use. The Helios Airways depressurisation is a good example of an incident where both flight crew were rendered incapacitated, so a system that does the equivalent of “Dave! Dave! We’re depressurising, unless you intervene in 5 seconds I’m descending!” would be useful. Then there’s the good old scenario of both the pilots falling asleep, as likely happened at Minneapolis, so something like “Hello Dave, I can’t help but notice that your breathing indicates that you and Frank are both asleep, so WAKE UP!” would be helpful here. Oh, and someone to punch out a quick “May Day” while the pilot’s are otherwise engaged would also help tremendously as aircraft going down without a single squawk recurs again and again and again.

I guess I’ve slowly come to the conclusion that two man crews while optimised for cost are distinctly sub-optimal when it comes to dealing with a number of human factors issues and likewise sub-optimal when it comes to dealing with major ‘left field’ emergencies that aren’t in the QRM. Fundamentally a dual redundant design pattern for people doesn’t really address the likelihood of what we might call common mode failures. While we probably can’t get another human crew member back in the cockpit, working to make the cockpit automation more collaborative and less ‘strong but silent’ would be a good start. And of course if the aviation industry wants to keep making improvements in aviation safety then these are the sort of issues they’re going to have to tackle. Where is a good AI, or even an un-interuptable autopilot when you really need one?


1. Kenedi (2016) found from 1999 to 2015 that there had been 18 cases of homicide-suicide involving 732 deaths.

2. No go alone rules are unfortunately only partially effective.


Kenedi, C., Friedman, S.H.,Watson, D., Preitner, C., Suicide and Murder-Suicide Involving Aircraft, Aerospace Medicine and Human Performance, Aerospace Medical Association, 2016.