A system for installation on aircraft to serve trays containing precooked food to passengers, the food-loaded trays being placed in the aircraft in the cold state and being heated to a service temperature level. The system includes a locker adapted to accommodate a bank of open-end racks, each having a stack of trays therein separated by air spaces, the front ends of the racks facing the door of the locker. Behind the racks is a hot air modulator in the form of a shallow box having a broad, continuously driven tape therein, the front course of the advancing tape facing the rear ends of the racks through windows in the box which register with these ends. The tape has endless trains of holes punched therein, each train lying in a plane intersecting a respective air space between trays in the stacks. Air drawn from the free region between the front door of the locker and the front ends of the racks is caused by a blower to pass through a heater station. The blower forces the air into the box from which the air is projected through the trains of holes into the air spaces to transfer heat in the food-loaded trays.