Permitting beards, regulating lengths
Other than tradition, there is no good reason for a the Indian Air Force to impose a blanket ban on beards. Sikh officers in all three armed services and the police force are allowed to wear beards and turbans. Beard-keeping is a tradition in the Indian Navy, and naval officers are allowed to keep beards regardless of their religious persuasion. Now, if operational reasons demand it—say, it gets in the way—it makes sense to ask the concerned officers to trim or shave their beards off.
Just like the armed forces have a sensible policy on haircuts, uniform and other aspects of turnout, they could have the same for beards, mustaches, sideburns and eyebrows. It need not involve religion at all, as long as it involves common sense.
The airmen who are fighting to keep their beards on their jobs might be motivated by religion. But the decision to allow them to keep them need not.