This is from one of those episodes where they tell three stories. This scene is from one where they tell three Christmas stories and is told by Grandpa.

If I’m remembering correctly the story is about grandpa and his brother help Santa while stationed in the Pacific during word war II after Burns shots Santa down. The above scene is at the end of the segment where Santa picks up grandpa and takes him to reunite with his brother who is living in Tahiti.

“We’ll get you up and running, or my name ain’t Young Grampa Simpson!”