If he [or she] is one of the pilots who are required to do border patrols and the distance from his place of residence is the distance that makes it permissible to shorten one's prayers -- which is approximately 80 km -- then it is permissible for him not to fast once he leaves the built-up area of his city and if necessity calls for him to break his fast before takeoff, there is nothing wrong with that.
If it is less than this distance and he has no choice but to undertake this mission so as to protect the interests of the nation, and he cannot undertake this mission unless he is not fasting, then it is permissible for him not to fast so as to achieve that interest and ward off harm.
Those who go back to their place of residence during the day and are no longer expected to come back on duty for the rest of the day have to do refrain from eating and drinking.
In all cases, they have to make up the fasts later on.
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