Question - what is the "swiss cheesiest" report?

[Lockwood]

I'm looking to lead a session on human factors in a non-rail setting. I have a few domain-relevant scenarios in mind.

Some of the training I got a few years ago followed an incident from some air accident that had terrible CRM. I don't remember much of it - CRM was the module of the training day I was looking forward to the most, but it was late in the day and on a long Teams session because they cancelled face to face training due to lockdown.

I was thinking of using a similar idea, taking a long incident from a different domain to discuss (to avoid focusing on the "I would never have made that mistake" trap).
I've seen several incident reports that have some good examples of the Swiss cheese model.

Are there any reports that people could suggest for this? I'm looking for something where lots of things lined up "perfectly", and is not a load of extreme technical nuance that outsiders would not understand. And ideally non fatal.


Very odd request, I know.

 

[Horizon22]

Most fatal incident investigations have an element of the "swiss cheese model" in them whereby multiple things have aligned (or gone wrong) in such a way which would not individually have led to disaster and loss of life but in turn each of them combined led to a fatal incident.

I know you are not looking for fatal incidents, but there will be quite a few RAIB reports which didn't lead to fatalities but certainly lots of things went wrong. Lewisham train strandings during Beast from the East perhaps in 2018? All the routes were locked in such a way that blocked up a huge chunk of South East London. The issue being missed originally by controllers, the train struggling to take power, a failure to declare it as failed, the lack of the route being de-iced - exactly because there was an emergency timetable - a sudden change in the weather to freezing rain, a gradual loss of power, on board trains with no toilets, communication failures etc.

 

[Purple Train]

The recent near miss at Bookham Tunnel springs to mind as one that was less serious but had an extraordinary stack of Swiss cheese slices. The report can be found here and as per custom here is the summary:

At around 11:42 on 29 April 2025, a passenger train was involved in a near miss with a team of three track workers walking through Bookham Tunnel, on the approach to Bookham station in Surrey. The train was travelling at 33 mph (53 km/h) as it passed the team. The track workers either moved to refuges inside the tunnel or stood against the tunnel wall as the train passed them. RAIB’s investigation found that the track workers were walking in a different location to that which had been blocked to trains and that neither the track workers, nor the signaller who had granted the line blockage, had realised this. This happened because the safe work pack, which formally detailed the safety arrangements for the task, incorrectly contained line blockage arrangements for the nearby Mickleham Tunnel, and not the tunnel around which the team was working. The error in the safe work pack had been introduced during the planning stage for the work and went unnoticed, despite the pack being checked multiple times during various stages of the safe work process.

I'm not sure if that one's too technical.

One that definitely isn't too technical but may not be a thick enough stack for you is the portable ramp incident at Norwood Junction. The report can be found here and here is the summary:

At around 09:52 on Tuesday 1 July 2025, a London Overground passenger train departed from Norwood Junction station with a portable access ramp attached. The ramp collided with the end-of-platform barrier and fell beside the track. No injuries were caused, although a member of station staff and a passenger needed to take action to avoid the ramp as it travelled down the platform. The portable access ramp was damaged beyond repair, and minor damage was caused to the train as a result of the accident. RAIB’s investigation found that a portable access ramp being attached at a doorway did not prevent the train’s doors from closing or from traction power being taken, because the ramp was of the incorrect type. Platform staff were unaware that the ramp they were using was of the incorrect type for the train involved. The correct ramp had not been available since September 2021 and none of the station checks in the period up to the accident had identified this. The train driver departed from Norwood Junction station with the ramp still attached as they believed it was safe to dispatch the train. The driver’s safety checks during dispatch were ineffective. Although some other factors may have been present, this was probably because the driver was distracted as they were making a mobile phone call at the time the train departed.

I suppose both of these go to show how far modern safety practices have come. These were two relatively benign incidents (although no doubt shocking and stressful for those involved) with a lot of varied factors. Talerddig was very similar, although sadly more serious. I think the railway has come so far in terms of safety that naturally we expect there to be a lot of Swiss cheese involved. In the wake of the Elstow crash, I think that came to the fore somewhat: we aren't used to "simple" accidents happening on the railway.

I will have a look through the RAIB archives and see if there are any more impressive stacks of Swiss cheese, but these are the two recent incidents which came to mind first. The Lewisham train strandings are a good example as well.
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EDIT:

I've just remembered an early RAIB report that may fit your criteria, although again it might be too technical. This was an incident where the door of a Class 222 came open just north of Kettering and the train ran for five minutes with the door open, due to two separate faults with the door system, one of which was the fact that a 2mm piece of dirt had been incorporated into the lock on manufacture. The train wasn't stopped immediately because the Train Management System software confused the driver into thinking that there was a fault with the passcom.

The report can be found here, and I have attached below the RAIB summary. Their diagram of the "Swiss cheese" factors can be found on page 42 of the report.

At 11:34 hrs on Saturday 10 June 2006, a passenger on train 1D17, the 10:30 hrs London St Pancras to Sheffield service, reported to on-board staff that an exterior door was open, in the first class portion, while the train was moving. The train was formed of a class 222 Meridian unit, number 222 009. The door opened just north of Kettering. The train was finally brought to a stand at Desborough summit, 5 miles 79 chains north of Kettering station, Figure 1. As intended by the design, when the door opened, the train’s brake applied automatically. However, the driver initially overrode this as, to him, the indications in the cab were ambiguous and he was uncertain what had happened. When the driver realised that the train was ‘in danger’, he made a controlled brake application to stop at the next signal. The train travelled for about five minutes with the door open before the driver braked the train to a stand.

Apologies for the long and wordy post, but I love an excuse to have a good trawl through minor RAIB reports and this is an excellent one!