March 2010 in Train Operations
Concern has been raised about axle isolations on High Speed
Trains (HSTs). A reporter believes a new instruction has been
issued by National Express East Coast (NXEC) regarding new braking
procedures that not all drivers are unaware of.
According to the reporter if any of the brakes are isolated on a HST the whole train should then be treated as if the brakes aren‟t working. The parts of the Rule Book concerning brake isolations are then followed.
The reporter states that NXEC issue a Form A if two of four axles are isolated. Form A imposes a five mph speed restriction which the reporter believes does not comply with the Rule Book which states speed restrictions relating to braking should be ten mph. Concern is raised that Form A does not comply with the standards governing the proportion of brakes that can be safely isolated.
The reporter also states that the new instruction allows NXEC to isolate one axle without informing the driver. He believes that if drivers are unaware of axle isolations already on their train then any further isolations they apply could result in defective brake applications and Rule Book breaches. The driver is concerned that this introduces a whole new set of rules not covered in the Rule Book and is leading to confusion amongst fellow colleagues. There is a suggestion that a lack of train maintenance and inadequate replacement of broken brake discs is resulting in an increase in regular brake isolations. The reporter does not understand why brake isolations are becoming routine. Additional information: The concern only affects old diesel 125‟s.
For the RSSB:
The amended instructions were a short term measure which were put in place due to a shortage of replacement wheel sets which affected not only ourselves but other operators in the country. Previously, it had been practice to isolate a whole vehicle's brakes when any defect was found on an individual wheel set and to then take the vehicle out of service. In order to reduce the impact on passengers by taking vehicles out of service and running sets short formed, a process of allowing vehicles to enter service with a limited number of wheel sets isolated was put in place, which was managed and monitored by our maintenance control team.
Before the changes were put in place a railway engineering consultant was engaged to do studies of the impact of the proposal on the trains braking performance. Feedback from the study validated the proposals as acceptable in line with the braking parameters shown in Railway Group Standard GM/RT2041 "Braking System Requirements and Performance for Trailer Coaching Stock‟.
Maintenance control staff use a table to calculate the speed restrictions that are imposed dependant on the number of wheel sets and these instructions were issued in a bulletin issued to all drivers. The frequency that this instruction is implemented is now very rarely applied as the underlying problem has now been resolved.
The Rule Book contains instructions in Section 3.4 of module TW3 which allow a locomotive-hauled train or HST to enter service, or continue in service, with the brakes isolated on a proportion of vehicles subject to a 10 mph reduction in speed. Section 3.2 explains that if a vehicle is equipped with two distributors, and only one of these is isolated, the vehicle must be treated as though the brakes are completely isolated on that vehicle.
However, these instructions are those issued to operations staff to apply nationally, and it is quite possible that an individual operator of HSTs might publish additional instructions directed to fleet staff that do not result in the effectiveness of the brakes being reduced significantly on any individual vehicle. National Express would be able to confirm whether this is the case.