An Evening Standard investigation into the Central line derailment, which shut the line six weeks ago, today pinpoints the cause.
The train’s revolutionary design, combined with its high speed, caused it to vibrate so much that bolts holding one of the motors in place were weakened. It eventually fell off on to the track, causing the train to derail at Chancery Lane station.
The Standard investigation also reveals a catalogue of mistakes and management failings in the two years leading up to the incident.
And insiders accused London Underground’s management of panic and inexperience for their decision to shut down the whole line.
The investigation also reveals the trains may never again run at their top speed of 60mph. Here we analyse exactly what happened.
The 85 Central line trains, built between 1990 and 1992 by ABB (now part of Bombardier), were the first Tube trains designed by a manufacturer rather than London Underground itself. This is now accepted as the reason why they have been so unreliable during their short lives. They were part of a £1 billion modernisation of the Central line that has been dogged by problems.
The trains, known as 1992 stock, have undergone a series of modifications since their introduction in April 1993. They suffered from water leaks, frequent failure of the destination display and other flaws that led to a high number of breakdowns.
LU engineers admit privately the newer the infrastructure the worse it performs. The most reliable trains are the ancient District line trains that date to the Seventies, and which have a failure rate one quarter of that on the Central line.
The design flaw only appeared in September 2001, when a motor became dislodged under a train. All the bolts holding the motors – of which there are 32 per eight-carriage train – were checked by ultrasound but no problems were found.
It was thought to be a one-off incident until, a year later, a motor dropped off an empty train at Loughton.
LU panicked and wanted all the 11,200 bolts to be checked every night. However, the infrastructure maintenance was in the hands of private company BCV. Its management, led by David Crawley, argued that daily inspections were impossible, as about half the rolling stock was left overnight in sidings. Instead, they agreed to checks every five days.
The arrangement, therefore, was governed by expediency rather that safety requirements – although it was endorsed by the Health and Safety Executive.
Moreover, it was the wrong type of check because the Chancery Lane accident was caused by bolts that sheared rather than came loose, and therefore tightening was neither necessary or helpful.
Yet, every night, more than 2,000 bolts were checked with torque spanners – spanners that were not verified for accuracy, which could result in over-tightening. Mistakes were inevitable.
As well as introducing checks, the management should have tried to develop an alternative to the existing bolts and brackets. Although there was a scheme to do this, it was half-hearted and there were concerns about the cost of replacing all the bolts. So very little happened until the Chancery Lane incident on 25 January.
One insider explained: “There was no sense of urgency or crisis. They had 18 months in which to come up with a scheme but did nothing.
Yet, within four days of the crash, they were displaying new bolts and brackets at a press conference-All this could have been avoided if they had acted quicker.”
WHY DID IT FAIL NOW?
Why had it taken eight years since the trains were introduced for the problem to occur?
The reason is that they were designed for automatic train operation (ATO) – in other words, to be driven by autopilot from LU’s central control. But teething troubles meant that until 2001 they had to be operated manually at lower speeds by drivers.
Since then, the driver has been present only as a failsafe and the trains have been operated remotely. For the first time, this allowed them to run at the full speed of 60mph and this is why the problem was not noticed until 2001.
At speed, the motors create vibration that is transmitted to the drive mechanism and appears to cause metal fatigue to the bolts. It could mean the trains will never be allowed to run at full speed again.
SHUTTING THE LINE
The big mistake in the immediate aftermath of the crash was to withdraw all the stock. That decision was made by LU’s chief rolling stock engineer, Malcolm Dobell, immediately after he visited the site on the day of derailment.
His view was endorsed the next day by BCV chief David Crawley and LU’s chief engineer Keith Beattie, and later by the LU board.
It is understandable that the stock was withdrawn because this was the fourth incident concerning motors coming loose. It showed the inspection regime was inadequate because the train had been checked just two days previously.
But the decision meant the service would be suspended for weeks, as the Health and Safety Executive then requires a case to prove that the trains are safe, something which is very hard to do.
Insiders report that there has been panic among managers responsible for running the Tube. It was like the national railway after Hatfield when, in October 2000, a broken rail caused the derailment of a train.
A lack of railway experience at the top levels of Railtrack led to the unnecessary imposition of 20mph speed limits around the network.
As a senior source in one of the infrastructure companies working on the Underground put it: “There are a lot of organisations involved in the running of the Tube, such as the HSE, LU and the infrastructure company.
“The real problem is getting anyone to be the first signatory on the piece of paper allowing the trains to be put back in service.
“Once the first person has signed, everyone else will follow. But no one is prepared to stick their neck out.”
Back in 1991, a similar incident happened on a District line train when a motor came off – but the stock was never taken out of service. Although 22 trains required modification the service was maintained throughout.
Nowadays, the Tube has far fewer operations managers with engineering experience.
They are unable to assess the real risk of a situation and tend to take conservative decisions using supposed safety considerations to mask their ignorance.
As one insider put it: “The only 100 per cent safe railway is one that is not running.”
While it is a massive task to replace all the bolts and the brackets holding all 5,600 motors, the real question is whether the trains are so dangerous they could not have operated.
And, tellingly – had the incident happened in a depot or on an empty train – would the whole stock have been taken out of service?
The universal answer from experienced railway managers was that the trains would have kept running.