54. The tests which were made before the Controller was fitted with a Man-Safety Tappet after the overwind revealed that, on one test when the engine was lowering an unbalanced load equivalent to the 44 men who were descending the shaft when the overwind occurred, the ascending cage attained a speed of about 63 feet per second before the Controller tripped in the "Slow Braking Zone ". Although the Controller caused the application of regenerative braking and mechanical braking to the winding engine, the descending cage passed the artificial landing used for the purpose of the test at a speed of about 19 feet per second. At the same time the ascending cage passed the corresponding artificial landing at the surface at a speed of almost 30 feet per second and subsequently it travelled about 60 feet past that landing before it was stopped.

55. If an artificial landing had not been used for the purpose of the above tests, the descending cage would have crashed into the baulks at the Silkstone Seam entrance at a speed of about 19 feet per second, which is about three and three quarter times the maximum landing speed of 5 feet per second prescribed by the statutory Regulation. Likewise the ascending cage would have passed the landing places in the headframe at a speed of about 30 feet per second and it would have been detached from the winding rope. In other words, there would have been an overwind very similar to that which occurred on 4th March, 1958.

56. During the above tests the Lilly Controller functioned correctly, but the defective Iversen Valve delayed the application of the mechanical brakes in the "Slow Braking Zone ". The air escape valve, however, was opened automatically in the "Fast Braking Zone ".

57. During the overwind on 4th March, the defective Iversen Valve delayed the application of the mechanical brakes by the winding engineman in the "Slow Braking Zone" and, moreover, the air escape valve was not opened in the "Fast Braking Zone ". It could not be opened because the engineman had put his brake lever into the "On" position and the linkage prevented the valve from being opened by the action of the Controller, as described in paragraph 42. The winding engine was decelerated, therefore, at a lower rate than it was during the above tests until the descending cage crashed on to the wooden baulks at the Silkstone Seam entrance. When that happened, however, the mechanical brakes became more effective automatically and the rate of deceleration increased considerably. In consequence of these circumstances the average rate of deceleration both during the overwind and the above tests was probably about the same.

58. As a result of the investigations I have come to the conclusion that the overwind on 4th March, 1958, occurred because, firstly, the winding engineman allowed the engine to reach a speed which was higher than the normal speed when the cages were approaching the end of the wind; secondly, the Lilly Controller was not equipped to prevent the engine from attaining that speed; and thirdly, the actions of the engineman and the Controller did not cause the speed to be reduced as quickly as the engineman expected and at the rate essential to prevent the overwind because :—

59. It follows from my conclusions that, from the point of view of preventing the overwind, it was immaterial whether the Lilly Controller tripped during the overwind because a trip could not have increased the rate at which the speed of the winding engine was already being reduced.