Lucy Letby: strikingly similar?

Show me a man who believes in conspiracy theories and I’ll show you someone who has never organised a surprise party.

—Lee Harvey Oswald.

The constant presence

Ordinarily, when a defendant appears on 22 counts of things like murder, there is a wealth of compelling evidence: eyewitnesses, fingerprints, incriminating forensics and related corroborations that point not just to murder, but to the defendant, specifically, committing each one.

Ms. Letby’s case seemed quite different. The evidence largely focused on whether, in each case, there had been a crime at all. Expert evidence challenged the presumption that the collapses were just part of the ordinary run of medical emergencies one would expect in a busy intensive care unit.

There was a curious missing step: the prosecution seemed founded on the tacit assumption that, as long as they could prove these to be malicious acts, it went without saying that they were carried out by Ms. Letby. This, it implied, could be inferred by her “constant presence”.

Was that tacit assumption justified?

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Prelude: tragedies in the air

On October 29, 2018, a Boeing 737-MAX operated by Lion Air, a carrier operating in Southeast Asia, crashed into the Java Sea, killing all on board. Five months later Ethiopian Airlines, a carrier operating in Africa, lost a Boeing 737-MAX when it crashed into farmland near Bishoftu.

At around the same time, there were a series of other air accidents: an Air Niugini Boeing 737 crashed into a lagoon in Micronesia. A Fly Jamaica Boeing 757 overran a runway in Guyana. A Saha Airlines Boeing 707 crashed in Iran.

Though all involved Boeing airliners the crashes seemed, as air crashes generally do, unrelated: they involved different airlines, on different continents, at different altitudes, over different terrain, at different times of the year and in different weather conditions.

Air crash investigators were called in and began to review the black box flight data records.

They soon began to notice unusual similarities between the two 737-MAX crashes.

MCAS: a villain in the room

Sometimes, when you look closely, the circumstances surrounding apparently unrelated events are so similar as to invite the inference that they have a common cause. Airline crashes are vanishingly rare and, except where planes crash into each other, are almost always unrelated.

They tend to arise from a complex mix of causes: pilot error, terrorism, atmospheric conditions, garbled air traffic control instructions, freight loading, autopilot mis-programming, mechanical malfunctions and even ground-to-air missile attacks. Each tends to be sui generis because the global aviation system learns from its mistakes. It is very good at isolating, minimising and not repeating catastrophic risks.

The two 737-MAX crashes stood out. They were uncannily similar. Both airliners were more or less brand new. Both crews experienced erratic altitude changes shortly after takeoff. In both cases, the computerised navigation system repeatedly, inexplicably, forced the plane’s nose down while the crew struggled to force it back to level. In both cases, the autopilot eventually overrode the crew’s manual intervention, whereupon the planes plunged irrecoverably towards the earth.

Air crash investigators soon identified a common culprit: Boeing’s state-of-the-art “Manoeuvring Characteristics Augmentation System” (MCAS) was installed on both airliners.

“MCAS” was designed to automatically push the plane’s nose down in certain conditions, to prevent stalling. But it relied on readings from a single “angle-of-attack” sensor, with no redundancy if it failed. When the sensor provided incorrect data, as it did in both cases, MCAS repeatedly forced the nose down. Boeing had not alerted airlines about the new system, and pilots were not trained how to manage it. The system could, in any case, override pilot inputs and there was no easy way to disable it in an emergency.

For those two 737-MAX crashes, there was a single villain in the room: MCAS.

A villain in the room at Countess of Chester?

With that analogy in mind, we come to the Countess of Chester Hospital in 2016. It had suffered, in effect, a series of baffling air crashes over a short period. But what had caused them? Was they just part of a random cluster, or was there a proverbial villain in the room?

Like airline accidents, individual hospital collapses tend to be independent. Each patient arrives with her own pathology, and her outcome depends on how effective the hospital treatment is on her pathology. Generally, when patients die, it is because the hospital could not