Halifax Question

Cees will probably be able to answer this but if anyone can help?
I was reading a first hand account of a Halifax crew returning from a raid over germany and they discover a hung up bomb on board. They open the bombdoors and some of the crew take turns bracing their knee on the bomb and chiping ice away? How is this possible? I am not familiar with Halifax bombays but in the Lancaster you only have small access panels above wach of the 16 bomb positions.