why the ---- you want to eat dry bread when flying F is beyond me.
but since you asked here is a scientific reply I saw before: enjoy, as they say ....

Retrograde toasters.
Breads are essentially networks of wheat flour protein molecules (called gluten) and starch molecules. Suspended in this network of molecules is carbon dioxide that is produced by the fermentation of yeast inside the dough. This gives bread its fluffy foam-like texture. Begin to play around with the amounts of these ingredients and other fancy tasting additives and you can get many different types of textures and tastes.
The starch inside of this mixture has its own characteristics. Starch molecules are made of two base components, both are long chain sugar molecules. Glucose (sugar) is classified as a monosaccharide, meaning one glucose unit. But if you link these units together, they can become a polysaccharide or complex carbohydrate. The two units are Amylose and Amylopectin. Amylose, which usually consists of about 10,000 sugar units, is built like a narrow bundle of reeds with all its glucose units arranged in straight parallel lines. Amylopectin, which usually consists of about 20,000 glucose units, has a more tree-shrub like appearance with its glucose units clumped together going in all directions. Plant starch is typically 20-30% amylose and 70-80% amylopectin. When heated up in the presence of moisture or water molecules, for instance placing the bread dough in the oven, the starch molecules weaken and allow water molecules to enter, or get in between the chains of the sugar molecules and join with them. This swells the starch granule and begins to soften it up, making it so warm and squishy! In the case of bread dough, the moisture can come from two sources, either the wheat protein in the bread itself or the water added to the mixture that makes up the dough. Once cooling begins, aka; the moment you take it out of the oven, the process begins to reverse itself and the starch molecules begin to “dry out” or crystallize and harden again, a process known as retrogradation. There is more water in the bread than the air. Once it evaporates to reach parity (in the dry environment of an aircraft or a fridge) the loss of water makes it dry. Toasting it accelerates the dryness. In a nutshell they should keep the still moist uncut bread in a ziplock bag until time to use it.