Now lets look to this photo (There is an bigger version but I cant find it on the web)
As anyone can see, there is an door under the cockpit. Is this an door used to access avionics on the ground or something like that ?
In 1974 I was hauling checks in the Northeast and we routinely used this door to board the plane. When it was frozen shut or had a latch problem, which happened, then we crawled around the sacks and cargo netting. If everything was working we used the front door. Schedules were tight and we were normally getting our clearances while the bags were getting loaded and offloaded.