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In addition to the pilot, small metal bars called life-guards, rail guards or (UK) guard irons are provided immediately in front of the wheels. They knock away smaller obstacles lying directly on the running surface of the railhead. Historically fenced-off railway systems in Europe relied exclusively on these devices and forwent the use of pilots, but this design is rarely used in modern systems.
Trams use in place of the pilot a device called a fender. Objects lying on the tram track get hit by a sensor bracket, which triggers the lowering of a basket shaped device to the ground preventing overrunning of the obstacles by dragging it along the road surface in front of the wheels.
In snowy areas the pilot also has the function of a snowplow.
The pilot was invented by Charles Babbage in the 19th century, during his period of working for the Liverpool and Manchester Railway. However, Babbage's invention was not built, and it is uncertain whether later users were aware of Babbage's idea.
On a mainline locomotive, the pilot has to successfully deflect an obstacle hit at speed; the ideal is to push it upwards and sideways out of the way. The locomotive should not lift on impact or the train will follow, and the ideal is for a fairly smooth structure so that the locomotive will not get caught and derailed.
The typical shape is a blunt wedge that is shallowly V-shaped in plan. In the later days of steam locomotives, the front coupler was designed to swing out of the way also, so it could not get caught up; this was called a drop coupler pilot.
Early on, pilots were normally fabricated of bars mounted on a frame; later on, sheet metal pilots were often used for their additional smoothness, and some cast steel pilots were employed for their mass and smooth shape. Early diesel locomotives followed the same plan.
Early shunting locomotives often had a pilot with steps on it to allow yard workers to ride on the locomotive; these were called footboard pilots. In some countries, footboard pilots are outlawed for safety reasons, and have been removed. Modern locomotives often have front and rear platforms with safety rails where workers can ride.
Most modern European rail vehicles must have pilots with snowplow function and rail guards by law. The required strength of the system is 30 kN (3,059 kp) in the middle of the track and 50 kN (5,099 kp) near the rails.
Modern US diesel locomotives have flatter, less wedge shaped pilots; this is because a diesel locomotive has the cab near the front, and the crew are vulnerable to impact from obstacles pushed up by the pilot.
To protect the crew and passengers, most modern locomotives and passenger cars are fitted with a device known as an anti-climber above the coupler to prevent colliding objects from travelling up over the frame and through the locomotive cab area or through the passenger car. Where a pilot is not fitted, a different type of anti-climber may be used. This is to prevent one passenger car from riding up over another, or telescoping in a collision.
- Hyman, Anthony (1982). Charles Babbage, Pioneer of the Computer. Oxford University Press. pp. 142–143. ISBN 0-19-858170-X. "Babbage suggested to Hodgson of the railway company what was later to be called a 'cow-catcher' for sweeping obstacles off the line."
- "§ 41 Bahnräumer und Schienenräumer". Verordnung über den Bau und Betrieb der Straßenbahnen (Straßenbahn-Bau- und Betriebsordnung - BOStrab) (in German). 2008-11-07. Retrieved 2009-03-29.
- "Notes and News: Pilot Engines, Past and Present". The Railway Magazine (Westminster: Railway Publishing Company) 91 (556): 117–118. March–April 1945. - describes seven other meanings of the word "pilot" historically used on Britain's railways.