RAIB report in to Carden Shaft accident at Durham

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aformeruser

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The full report is here:
http://www.raib.gov.uk/cms_resources.cfm?file=/120702_R122012_Durham.pdf

The summary of conclusions is as below:

RAIB said:
Immediate cause
152 The cardan shaft became detached and was not retained by the safety loops (paragraph 75).

Causal factors
153 The seizure of the outer bearing on the input shaft of the final drive was the causal factor in the cardan shaft becoming detached (paragraph 81).
154 The seizure of the outer bearing was due to the combination of the following factors:
a. the specified end float was small considering the high temperature difference across the bearing rings (paragraph 92, Recommendation 1);
b. the actual installed end float was less than that measured at installation
(paragraph 94, Recommendation 1); and
c. the uncontrolled level of misalignment led to additional loads on the bearings
increasing their running temperature and further reducing the operating end
float (paragraph 97, Recommendation 1).
155 It is possible that the following were factors in the seizure of the outer bearing:
a. the introduction of GS090 in January 2009 may have further reduced the
operating end float on the bearings (paragraph 100, Recommendation 1);
b. the specified end float measuring technique may have over-estimated the
installed end float (paragraph 102);
c. the testing as specified in WI-27 may have been inadequate to detect the
problem with the end float setting (paragraph 105, Recommendation 5); and
d. the input bearings may have been starved of oil cooling thereby
increasing their running temperature and reducing the operating end float
(paragraph 111, Recommendation 1).
156 The seizure of the outer bearing was not detected by the lift checks and this was a causal factor (paragraph 123, Recommendation 3).
157 The detached cardan shaft was not retained by the safety loops and this was a causal factor. The safety loops did not retain the cardan shaft because of the following factors:
a. the design of the safety loops was unable to retain a rotating cardan shaft
(paragraph 119); and
b. the geometry of the design was such that the detached cardan shaft could
exit the cradle formed by the safety loops without requiring any deformation
(paragraph 121).

Underlying factors
158 The underlying factors were:
a. the original SCG product manual for the overhaul of RF420i final drives
was not available to the TESCO when developing WI-27 (paragraph 129,
Recommendation 4);
b. LH had no access to the original design drawings for the final drive
(paragraph 130, Recommendation 4); and
c. LH introduced design changes to the setup of the final drive without assessing
the effects of the changes (paragraph 132, Recommendation 2).

Additional observations
159 Although not linked to the accident on 10 April 2011:
a. there was a lack of control measures in place during the recovery phase of the accident (paragraph 142, Recommendation 6);
b. the modification to replace the selector fork might make the alignment of the input and pinion shafts more critical (paragraph 144, Recommendations 1
and 2); and
c. at low speeds, the cardan shaft operates with large deflection angles and the difference in deflection angles exceeds the manufacturer’s recommended limit (paragraph 146).
 
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142094

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Should make for some interesting reading, especially since I am very likely to be getting a 142 on my journey in 48 minutes time...
 
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