It's been a few years since I marshalled an aircraft but I believe the principle is still the same. Aircraft taxi independently along the clear taxiway areas. When entering an area with moveable obstructions such as ground equipment and vehicles, taxying is done under the guidance of a marshaller. The marshaller is better positioned to judge obstacle clearances than the aircraft crew. Shining bright lights in the marshaller's face leaves him unable to see the obstacles let alone the clearances.
A marshaller blinded by taxi lights has an obligation to signal the aircraft to stop and not allow it proceed until such time as he can properly see the whole aircraft and all potential obstacles. If he doesn't then he may be held responsible for the consequences. On the other hand a pilot who ignores the marshaller is responsible for the outcome. In reality though we are supposed to be a team, working together to ensure flight safety from start to finish of every flight. Or has CRM finally eliminated aircrew confidence in the groundcrew?
Somewhere out there is an ex-Vulcan pilot who ignored my stop signal and buried his left main three feet deep in the Lincolnshire soil. He spent the rest of the night with a spade in his hand digging the b*gger out again, after a wise old Group Captain told him "You put it in there, now get it out!" I bet he's never ignored another marshaller since then...
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Through difficulties to the cinema