PL-1 was the designation for pilots.
Prior to the start of the Bacta War, all of Rogue Squadron's X-wings and other equipment were sold off as surplus, the reason that they were missing parts like PL-1's. Commander Wedge Antilles thought this was the New Republic's covert way of helping their cause of liberating the planet Thyferra from former Director of Imperial Intelligence Ysanne Isard.