February 2011 in London Underground
A reporter is concerned that some 'wheel flat' defects on London Underground trains are not being treated seriously. Consequently, it is believed trains are being put back into service against the advice of Engineers.
There is a Minimum Acceptable Condition Standard (MACS) for
wheel flat defects which states that defects of more than 30mm in
diameter should be rectified before a train returns to service. The
reporter emphasises that this rule is being adhered to. However,
where there are multiple wheel flats on a single wheel, it is not
clear whether or not a train should be allowed to back into
The reporter describes scenarios where wheels have had up to eight flats of between 10 and 25mm in diameter. In such cases, there is no applicable standard. Whether it is safe or not to send a train back into service normally depends on the advice of Engineers and a final decision made by the Fleet Manager.
The reporter is concerned that sometimes Fleet Managers appear able to override the advice of Engineers who state that a train should not be allowed to return to service with multiple wheel flats. Staff may then be pressurised to return trains to service when it may be unsafe to do so.
Thank you for raising this issue. There have been a number of associated problems recently on London Underground fleets which have involved engineering assessments being carried out and concessions to standards being agreed and implemented. However, none of these concessions would allow the scenario described by the reporter above. These concessions typically allow single wheel flats up to 60mm in length and multiple wheel pitting defects within specified limits and usually for limited time periods. In one case wheel flat depth dimensions were also used as a method of control. All such concessions are agreed by licensed Engineers and accepted by the Professional Heads of Rolling Stock and Track. In most cases detailed measurements were undertaken to support the decision to allow the concession.
Regardless of any concessions in place, current standards do allow multiple wheel defects such as minor wheel surface cracks or wheel cavities, but do not currently cover multiple small wheel flats. There are current plans to review wheel-set standards to consider acceptable criteria for multiple wheel flats. This is on the basis of the experience gained from the work undertaken to assure the concessions granted above and on the basis that multiple small wheel flats on the same wheel is equivalent to the same sized wheel flats on different wheel-sets. Clearly if a wheel has eight separate wheel flats of between 10mm and 25mm then this should be regarded as an abnormal defect and it is expected that this would be referred to a specialist Engineer for advice (see below for information on the role of the specialist Engineer).
With regard to the point raised about over-riding the advice of Engineers, currently depot based Engineers are required to seek advice from specialist Engineers for all abnormal defects, safety issues or identified non-compliances with standards. London Underground employs licensed specialist Engineers who have delegated responsibilities from the Professional Head of Rolling Stock under Railway and Other Guided transport systems Safety regulations 2006 to provide advice and recommend the most appropriate solutions. If they are aware that their advice is being ignored then they are duty bound to escalate the issue to the Professional Head of Rolling Stock who will take appropriate action to ensure that the correct approach is taken - even if that means preventing the train (or trains) from being offered for passenger service.