Important Aylesbury depot work contributes to high-performance and passenger satisfaction

Posted: 15 May 2009 | | No comments yet

How the train maintenance team at Aylesbury Depot play a vital part in helping Chiltern Railways achieve one of the highest PPM scores among UK rail companies.

How the train maintenance team at Aylesbury Depot play a vital part in helping Chiltern Railways achieve one of the highest PPM scores among UK rail companies.

Chiltern Railways achieves one of the highest PPM scores among UK rail companies and in the last period they achieved the highest score ever in a four week period. So what does it take to make this railway so reliable? In part, this is due to the work that is carried out by the train maintenance team at Aylesbury Depot.

If you’ve ever been to Aylesbury Station you may have seen the depot in the distance and wondered what happened there. Inside lots of duties are undertaken including routine maintenance, ranging from a simple fuel point check, A up to B exams, heavy maintenance (engine, bogie, wheel set change), tyre turning and air conditioning maintenance.

The A exams

All routine maintenance on Chiltern Railways fleets is carried out based on mileage. he current maintenance plan for both Class 165 and 168 DMU fleets comprises of three A exams (A1, A2 and A3) which are carried out every 5,000 miles, followed by a B exam every 20,000 miles.

The A1 and A3 exams are identical in their scope of work, which is equivalent to an advanced fuel point check and encompasses some of the following checks: engine oil, coolant levels, toilets, checking the tripcock, (this is a safety system required for parts of the Chiltern route that run over London Underground infrastructure) checking the cab and passenger areas to ensure there is no damage and that the unit is safe and ready for traffic. Depot staff also carry out checks for faults that drivers may have reported during the train’s duties. Quick feedback from drivers and other members of the Operations team helps with on going reliability improvements. An A exam would normally take about one and a half hours and is followed by a thorough interior clean.

The A2 exam is carried out after 10,000 miles to check all the safety systems, brake pads, bogies, oil levels, engine air supply as well as many of the things mentioned above.

The B exam

The B exam covers the majority of on-board systems and equipment and takes place every 20,000 miles. The B exams range from a B1 to B12 with the content differing slightly on each exam ensuring that all required areas are covered at the appropriate frequency, but also that each exam takes approximately the same amount of time. This is particularly important for resource and workload planning. The exam starts with an under frame clean to remove all the dirt and debris from underneath the train, removing potential fire risks and allowing the technicians to examine component parts in more detail. The wheels, dampers and suspension are also checked to help ensure that Chiltern Railways passengers have a smooth ride throughout their journey. The maintenance team also check the engine and change the oil and the filters and simulate movement to ensure our safety systems are working correctly. As well as traction and under frame systems, passenger facing systems including doors, CCTV, air conditioning, toilets are covered in the B exam cycle. During each exam, it is important that the depot identifies potential failures that could have an impact on reliability and that these are either rectified as part of the exam, or if required, containment measures are put in place to ensure that it does not impact on our performance.

However, with 90% availability required to run our service, it is essential that when a unit is at Aylesbury for its B exam the depot staff will also carry out heavy maintenance activities and modifications to help further improve reliability and enhance the passenger environment. So whilst the b exam is progressing it may also have an engine change and wiring for a new CCTV system installed.

Fuelling and emptying the toilet

When there is approximately 100 miles of fuel left in a unit, it will be brought in to do a fuel point check and it will be refuelled. Fuel point checks are predominately carried out at Wembley Depot; however Aylesbury also has the capability to carry out this task. Prior to coming into the depot, the toilet tanks are emptied. After this, the train comes inside the depot where it is refuelled and fresh water put into the toilet tanks. Fuelling the train is similar to refuelling a car in a petrol station. However prior to filling it up, each train number is electronically logged enabling the depot to monitor fuel levels and consumption.

Train safety

Train safety is of paramount importance and Chiltern Railways use a number of different safety features. On the line from Marylebone to Aylesbury Vale Parkway, Chiltern Railways also shares some of the route with the London Underground and so share their safety systems. Elsewhere on the route, there are nationwide systems; Automatic Warning System, and Train Protection and Warning System (TPWS). In addition to these, Chiltern Railways also has Automatic Train Protection (ATP) fitted to all our main line trains, one of only two operators in the UK who use this advanced train protection system.

The AWS is fitted throughout our route and on track magnets ‘speak’ to the train about signals ahead. If the signal is not green then a horn sounds to alert the driver. If he doesn’t respond to the warning then the brakes come on automatically to bring the train to a halt. TPWS is also standard throughout the UK. This system is always running in the background and would apply the brakes if the driver was to speed or go past a red signal on a critical part of the network. Both lines south of Banbury Chiltern have ATP fitted – this feeds more information direct to the driver’s cab informing him of speed changes and signal aspects coming up. If the driver fails to react to these the train will automatically intervene to reduce the speed. While maintaining up to four train braking safety systems is an onerous task, these are maintained to a high standard to ensure safe operation and reduce risk of reliability related failures.

Maintaining good wheel condition is another important factor in maintaining good fleet reliability. The engineering team keep a close eye on them using routine maintenance techniques – wheels are regularly checked at the depot. In addition, information is received from an on track system at Banbury called Gotcha which automatically checks for wheel damage every time a train passes over it. Wheel re-profiling is carried out on Chiltern’s dedicated Talgo lathe.


These are just some of the things that trains go through at Aylesbury Depot to ensure that they stay safe. Of course, there are times when trains will report particular faults, so for this Chiltern have a team of dedicated specialists who are on duty 24 hours a day. This ensures that once a unit enters service any problems that occur are quickly captured and scheduled in for investigation prior to re-entering service.

The team at the depot and across the rest of our sites work to get the big things right and to ensure that comments from passengers and drivers are sorted as quickly as possible. This could be why Chiltern Railways achieves such record breaking performance and passenger satisfaction.

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