Runaway tram accident investigation report

AuthorityDepartment of Environment, Food and Agriculture
Date received2018-12-10
OutcomeAll information sent
Outcome date2019-03-19
Case ID675466

Summary

The requester asked for the Health and Safety at Work Inspectorate (HSWI) investigation report into the August 2017 Snaefell Mountain Railway runaway tram incident, noting that legal proceedings had concluded. The Department of Environment, Food and Agriculture disclosed all requested information, providing a 53-page report containing the executive summary, technical findings, and recommendations.

Key Facts

  • The request concerned the runaway Snaefell Mountain Railway tram incident that occurred in August 2017.
  • The Department of Infrastructure (DoI) pleaded guilty to five charges and was fined £18,000 in a related court case.
  • The authority released the full HSWI accident investigation report, which spans 53 pages and includes 4 documents.
  • The report details technical failures including the pressure gauge, low pressure alarm, and Fell brake systems.
  • The response was issued on 2019-03-19, confirming that the conclusion of legal proceedings removed previous disclosure exemptions.

Data Disclosed

  • August 2017
  • £18,000
  • five charges
  • 2018-12-10
  • 2019-03-19
  • 53 pages
  • 4 documents
  • IM596431

Original Request

Please supply me with a copy of the HSWI accident investigation report into the runaway Snaefell Mountain Railway tram incident in August 2017 - preferably the full report, but certainly an executive summary. The court case was heard last week - the DoI pleaded guilty to five charges and was fined £18,000. As legal proceeding are now concluded this can no longer be a reason for disclosure to be exempted as per my original FoI request on this matter - IM596431

Data Tables (12)

The air system is only currently on the trams for operation of the motor/brake and the reverser
switches and the system settings and interaction with the other control systems in the trams was
not changed when the contactors were changed to electromagnetic operation. This needs
addressing with a review of the control system, irrespective of whether the motor/brake and the
reverser switches change to electromagnetic operation or remain pneumatically operated.
The Type Test that the IoMT engineers intend to undertake in proving the newly manufactured Fell
brake must include an overspeed test at Crush load. The speeds chosen should be working up to
double the normal maximum line speed, perhaps 15 mph, 20 mph and 25 mph. The brake shoes
should be inspected for abnormal wear and allowed to cool between the overspeed tests. This
testing should also be used to verify the test procedure used as the routine test for the Fell brake, as
it appears there is no historical data I am aware of to confirm this as a valid test.
When the cast iron combined brake shoe and carrier is Type Tested, this should also be tested in
Tare & Crush loads plus at least one overspeed test to verify the performance with the change of
friction material is equal or better than the mild steel shoes.
This report has been prepared following a visit to the HSWI workshop at Thie Slieau Whallian, St
Johns, for the inspection of the Fell brake mechanisms removed from Tram 2, following the previous
visit in March 2018 to inspect Tram 2 and the location where the incident occurred in August 2017.
There were discussions with a number of the Inspectors from the HSWI.
It was observed that there is a crack in the strengthening rib on the rear of one of the fabricated
carriers, and that it was adjacent to a weld which suggested that the weld was a repaired crack. It is
clear, on looking at the brake shoe, that the carrier has been bending when the brakes are applied
under the forces of the Long levers at each end, wearing each end of the brake shoe more than the
centre which has resulted in the crack in strengthening rib. This then just exacerbated the wear at
the ends of the brake shoe resulting in little or no wear in the centre. Figure 2 shows this carrier
and brake shoe.
Item Description Comment
02 Brake Shoe Carrier and Brake Shoe assembly New design will be one piece “Slipper casting”
03 Long lever
04 Top lever
05 Sway link
06 Retaining ring
07 Thrust plate
08 Assembly of “T” shaft (Threaded rod) and Mounting block
11 Locking ring
12 Middle pin
14 Bogie casting location screw
15 Sway link pin
16 Brake shoe carrier location pin New design “Slipper casting locating pin”
Snaefell End - Outer
Item Location Measurement Concave Remarks
Max. Min
Slipper casting location Pin 1* 0.714” - N/A Outer or inner
Slipper casting location Pin 1* 0.705” - N/A Inner or outer
Bogie casting location screw A3 1.232” - N/A
B3 1,225” - N/A
Screw Centre 1.235” - N/A
Middle Pin B4 0.740” 0.735” N/A
C4 0.740” 0.738” N/A
Middle Pin A5 0.740” 0.736” N/A
D5 0.740” 0.736” N/A
Sway link location Pin C6 0.990” - N/A
D6 0.985” - N/A
E6 0.993” - N/A
F6 0.993” - N/A
Long lever A A1 0.772” 0.770” Yes
A3 1.258 - Yes
A5 0.765” 0.760” Yes
Long lever B B2 0.778” 0.770” Yes
B3 1.255” 1.253” Yes
B4 0.770” 0.770” Yes
Top lever C C4 0.767” 0.763” Yes
C6 1.024” 1.018” Yes
Top lever D D5 0.767” 0.761” Yes
D6 1.042” 1.022” Yes
Sway Link E & bush E6 1.167” 1.165” No
Bush 1.160” 1.156” N/A Outer diameter
Bush 1.007” 1.003” Yes Inner diameter
Laxey End - Outer
Item Location Measurement Concave Remarks
Max. Min
Slipper casting location Pin 1* 0.700” - N/A Circular Outer or inner
Slipper casting location Pin 1* 0.703” - N/A Circular Inner or outer
Bogie casting location screw Headstock 1.235” 1.212” N/A
A3 1.182” 1.162” N/A
B3 1.175” 1.165” N/A
Bogie Casting 1.225” 1.215” N/A
Screw Centre 1.235” N/A
Middle Pin B4 0.740” 0.737” N/A
C4 0.742” 0.729” N/A
Middle Pin A5 0.745” 0.739” N/A
D5 0.738” 0.735” N/A
Sway link location Pin C6 0.990” - N/A
D6 0.980” - N/A
E6 0.990” - N/A
F6 0.990” - N/A
“T” shaft & Mounting block E7 0.980” 0.975” N/A
Long lever A A1 0.800” 0.790” Yes
A3 1.325” 1.315” Yes
A5 0.792” 0.782” Yes
Long lever B B2 0.795” 0.785” Yes
B3 1.332” 1.332” Yes
B4 0.788” 0.786” Yes
Top lever C C4 0.755” 0.745” No
C6 1.006” 1.000” No
Top lever D D5 0.757” 0.755” No
D6 1.007” 1.000” No
Sway Link E E6 1.025” 1.023” Yes
E7 1.030” 1.020” Yes
Retaining ring F6 1.005” 1.005” No
Laxey End - Inner
Item Location Measurement Concave Remarks
Max. Min
Slipper casting location Pin 1* 0.705” - N/A Circular Outer or inner
Slipper casting location Pin 1* 0.710” - N/A Circular Inner or outer
Bogie casting location screw Headstock 1.225” 1.210” N/A
A3 1.178” 1.153” N/A
B3 1.178” 1.151” N/A
Bogie Casting 1.220” 1.212” N/A
Screw Centre 1.235” N/A
Middle Pin B4 0.736” 0.732” N/A
C4 0.742” 0.733” N/A
Middle Pin A5 0.745” 0.735” N/A
D5 0.736” 0.730” N/A
Sway link location Pin C6 0.990” - N/A
D6 0.990” - N/A
E6 0.990” - N/A
F6 0.990” - N/A
Long lever A A1 0.797” 0.790” Yes Bent by 9mm
A3 1.325” 1.319” Yes
A5 0.790” 0.785” Yes
Long lever B B2 0.800” 0.783” Yes Bent by 6mm
B3 1.330” 1.325” Yes
B4 0.780” 0.775” Yes
Top lever C C4 0.755” 0.753” No
C6 1.007” 1.003” No
Top lever D D5 0.755” 0.752” No
D6 1.008” 1.003” No
Sway Link E E6 Yes
Retaining ring F F6 1.003” 1.003” No
Laxey end
Thread from top Measurement of thread depth
3** 0.165”
4** 0.155”
5** 0.165”
Nominal thread 0.180”
Summit end
Joint No. Outer Inner Multiplication factor Outer Inner
B, C A, D
1 0.023” 1.9655 0.045”
2 0.068” 1.9655 0.134”
3 0.030” 2.966 0.0.089”
3 0.026” 2.966 0.078”
4 0.029”
5 0.031”
4 0.032”
5 0.030”
6 0.034”
6 0.057”
Sub Total 0.229” 0.330”
6 bush 0.011”
6 0.010”
7 *
Total 0.580”
Laxey end
Joint No. Outer Inner Multiplication factor Outer Inner
B, C A, D B, C A, D
1 0.092” 0.100” 1.9655 0.181” 0.197”
2 0.090” 0.092” 1.9655 0.177” 0.181”
3 0.163” 0.167” 2.966 0.483” 0.495”
3 0.172” 0.189” 2.966 0.510” 0.560”
4 0.051” 0.047”
5 0.053” 0.055”
4 0.022” 0.020”
5 0.026” 0.023”
6 0.016” 0.017”
6 0.018” 0.017”
Sub Total 0.753” 0.784” 0.776” 0.836”
6 0.035” 0.035” *
7 0.055” 0.055” *
Total 1.627” 1.702”
Aggregate 1.6645” (42.28mm)

Full Response Text

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21st March 2018 Contents 1. Introduction .................................................................................................................................... 3 2. Background ..................................................................................................................................... 3 3. Executive Summary ......................................................................................................................... 5 4. Inspection findings .......................................................................................................................... 6 4.1. Pressure Gauge and Low Pressure Alarm ............................................................................... 6 4.2. Fell brake ................................................................................................................................. 6 4.2.1. General ............................................................................................................................ 6 4.2.2. Fell Brake Tram 2 ............................................................................................................ 8 4.2.3. Fell brake Tram 1............................................................................................................. 9 4.2.4. Testing ............................................................................................................................. 9 4.2.5. Procedures .................................................................................................................... 10 4.2.6. Training ......................................................................................................................... 10 4.3. Wheel brake system.............................................................................................................. 10 5. New Fell Brake mechanisms ......................................................................................................... 11 6. Discussion ...................................................................................................................................... 12 6.1. Newtonian calculations ......................................................................................................... 12 6.2. Fell rail height effects ............................................................................................................ 12 6.3. Brake shoe friction coefficient. ............................................................................................. 13 7. Observations ................................................................................................................................. 13 7.1. Pressure Gauge and Low Pressure Alarm ............................................................................. 13 7.2. Low Pressure Switch ............................................................................................................. 14 8. Conclusions ................................................................................................................................... 15 9. Recommendations ........................................................................................................................ 16 10. References ................................................................................................................................ 16 Annex A – Fell brake setting drawing. .................................................................................................. 17 Annex B Calculations ............................................................................................................................. 18 B.1 General. ..................................................................................................................................... 18 B.2. Assumptions, Symbols, Observations and Gradients. .............................................................. 18 B.3. Calculations ............................................................................................................................... 19 B.3.1. Scenario from the start of the incident to the arrival at the Bungalow (Fell brake application only) ............................................................................................................................... 19 B.3.2 Scenario from the arrival at the Bungalow to the final stop (Wheel brake & Wheel & Fell brake applications) ............................................................................................................................ 19 B.4. Fell brake braking Force – design. ............................................................................................. 20 B.5. Wheel brake .............................................................................................................................. 21 Annex C Extract from Fell rail data ....................................................................................................... 23

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21st March 2018 1. Introduction This report is prepared for the Health and Safety at Work Inspectorate (HSWI) of the Isle of Man and has been written by Mr , an independent Railway Brake Specialist.
Mr has been a Consultant since retiring in 2008 working in UK and abroad. He commenced his braking career in 1975 working for Davies & Metcalfe as a design engineer rising to Technical Manager at the time of the merger in 1997 with SAB Wabco. He was Technical Director of SAB Wabco UK until 2007 when he became Group Technical Advisor until retiring in 2008. He has been involved in the design of railway brake components and railway brake systems since 1975. This encompassed the Graduable Release Automatic Air Brake Systems within Europe, Africa and Australia, the Direct Release Braking Systems in the USA, South Africa and Australia, and Direct EP Brake Systems across the world. He was Chairman of the Railway Division of the Institution of Mechanical Engineers in 1992/93 and was a Vice President of the Institution from 1994 until 1999. This report has been prepared following a visit to the Snaefell Mountain Railway (SMR) depot at Laxey for the inspection of the braking systems, and related equipment, on Trams 2 & 1. There were discussions with a number of the SMR depot staff & engineers from the Isle of Man Transport (IoMT). A visit to the Bungalow station and the location where the Tram 2 stopped was included.
2. Background The SMR was built in 1895 and runs from Laxey to the summit of Snaefell at 620m above sea level.
The line operates with the majority of the Victorian rolling stock that was fitted with the Fell and Wheel braking systems from the inception of the railway. In 1977 the vehicles were equipped with more modern, but second-hand, traction equipment with new bogies which enabled dynamic braking to be employed. This dynamic brake has been the primary brake since that time with the Fell brake as a back-up or an emergency brake. The incident resulting in this report occurred on 4th August 2017 at around 1445hrs. The weather conditions were dry, clear and still with good light conditions and Tram 2 was fully laden, with 2 crew and 48 passengers, commenced the downhill run to Laxey from the summit. A few moments into the journey, between poles 1144 and 1134, the motorman identified that there was a problem with the rheostatic control system and there was no response from the electric traction/brake controls. He applied his Fell brake, eventually to its maximum, and signalled the conductor/brakesman in the rear of the tram who had already applied his Fell brake, also to its maximum, as the conductor had realised there might be a problem prior to the signal received from the motorman. The crew reported that there was no reaction from the Fell brake between the point of application and the A18 crossing, a distance of approximately 900m. The tram travelled a further 500m, through the Bungalow station at a reduced gradient, across the relatively flat road crossing, then onto the reduced gradient until continuing on the 1:12. The crew applied their Wheel brakes at the Bungalow station as there is no Fell rail available here or during the road crossing. The tram was eventually brought to a halt between poles 1109 & 1108 using the front and rear Fell brakes and the Wheel brakes. There were no injuries or fatalities during, or resulting from this incident The extent of the uncontrolled part of the journey was measured by HSWI inspectors and found to be approximately 1400m and the speed was measured by the railway operator’s remote equipment,

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21st March 2018 the maximum speed being recorded as 44.1mph. There is a track speed limit of 12mph and at the level crossing a limit of 5mph. There are no functioning speedometers in the cabs. The breakdown of a micro-switch was the primary cause of the incident, not restarting the compressor allowing the compressed air system to deplete and fall below the setting of the pressure switch which cuts of the electric traction and braking system, hence the loss of dynamic brake. The main reservoir pressure was shown on two small 50mm diameter pressure gauges located in the left hand top corner of the cab on Tram 2. Since the incident on 4th August 2017, Tram 1 has had its original Fell brakes replaced with ones manufactured to recent drawings produced by the Isle of Man Transport Engineering team. The cab “dashboard” in Tram 1 has also been modified.

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21st March 2018 3. Executive Summary The removal of the control of the rheostatic brake by the Low Pressure Switch (LPS) without any previous warning except observation of the small pressure gauges was the occurrence that started the incident and brings into question several aspects of the electrical and pneumatic control and of indications for the motorman. The size and location of the pressure gauge has been addressed as has the provision of an audible alarm for falling pressure. A red and green banding (cut off pressure down to the alarm setting) has been added to show the acceptable pressure limits, but it will give greater assistance to mark the cut-in to cut off pressure of the compressor governor by the green band and have the red band below the cut-in pressure. The cut off pressure for the removal of Traction/Brake is set at 40 p.s.i. and the new audible alarm is set at 50 p.s.i. There needs to be at least 20 p.s.i. left in the air system to allow the full descent under rheostatic brake before the 40 p.s.i. switch cuts it off therefore consideration should be given to raising this alarm setting to 60 p.s.i. There have been changes to the method of operation of the contactors in the traction/braking circuits with no changes to the control circuit interlocks such as the LPS. A review should take place to see if the circuit can be reconfigured to maintain the required functionality, but remove the necessity to switch off the dynamic brake. The Fell brake mechanisms on Tram 2 were both extremely worn, and at least one at the Laxey end was set higher than the established reference height, as measured in the depot. The other end had moved during previous testing following the incident so the actual set height is uncertain. The data available suggests the Fell brakes were only giving about a quarter of the retarding force it should have been capable of to perform a stop from 12 m.p.h. with one Fell brake. This leads to the conclusion that the combination of excessive wear in the mechanism and brake shoes, high height setting and low Fell rail height gave a low clamp force on the Fell Rail, and the brake shoes may have been actually running on the top of the Fell rail. The addition of the Wheel brakes at the Bungalow station gave the additional retarding effort to bring Tram 2 to a halt. The Fell brake assembly and components had no drawings or setting information prior to the incident with Tram 2 and the IoMT engineers have produced a set of drawings to replicate the mechanism with renewable bushes in the pin/lever interfaces. The mechanism has been laid out with the relative position it will adopt with new brake shoes, 10mm worn shoes and displaced Fell rail simulating bogie movement and the Tare setting position has been determined.
The Work carried out by IoMT engineers in producing the newly manufactured Fell brake as fitted to Tram 1 has been a robust process. It has produced a mechanism that in my opinion, if setup to the height determined from that exercise, will give the performance that would have been expected from the original Fell brake as manufactured. The consistency between components by the manufacturing methods should ensure a consistency of braking load on to the brake shoes between all the brake locations. The proposed shimming of the brake mounting beam to prevent movement will stop any tendency of the mechanism to lift up if excessive force is ever applied to the Fell brake operating handwheel. There are recommendations for the setup procedure of the Fell Brake in the depot and for overspeed testing during the Type Test of the newly manufactured Fell brake assembly and when cast iron replacements for the brake shoes are trialled. The Wheel brakes performed to give a retarding force as expected. The speedo that has been fitted has an electrical input driven from the GPS signal, so it should be possible to provide an overspeed alarm for the motorman.

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21st March 2018 4. Inspection findings 4.1. Pressure Gauge and Low Pressure Alarm The original “dashboards” in the trams were to a variety of layouts. Those in Tram 2 had two 25mm pressure gauges on the extreme left of the cab and Tram 6 had a gauge with two concentric needles to the right of the cab centreline. The redesign fitted to Tram 1 has a 100mm pressure gauge more central to where the motorman will stand reading main reservoir pressure. This is a significant improvement for the motorman to be able to observe the main reservoir pressure. A red and green banding has been added with the green band showing switch off pressure for the compressor (102 p.s.i. – 7 bar) and the pressure of the new audible low-pressure alarm (50 p.s.i. – 3.4 bar). The Low Pressure Switch (LPS) is situated in the control circuit to remove power to the motor or rheostatic braking circuits. This will instantly remove the rheostatic brake which requires the motorman to immediately commence using the Fell brake to maintain the tram speed. Any significant delay will enable the tram to accelerate, as happened on the 4th August 2017. The contactors used for the braking resistors have been changed to electroma

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