Guppies should not feel alone --- according to a Douglas instructor, the MadDog had a built-in cooling problem. The DC-9 was designed for a supply of cold air from the aft, (either an airhose connection or the APU), so to equalize cabin temps, the duct holes got larger toward the front. Then jetway-mounted hoses came along, so Delta ordered forward connection ports. This caused the long cabin to be cold in front and hot in back, unless you started the APU.

Without sandbags in the forward cargo bin, an empty MadDog would get tail-heavy on the ramp, trip the ground shift relay, and block the APU from battery starting. First flight of the day at an outstation: "OK, you all please come to the cockpit and jump up and down!"