Now on board The Prydwen, your goal is to plant three explosives at the uppermost section of the airship. You can go in guns blazing (for lots of loot and experience), or you can try more discrete infiltration methods. You can sneak with a stealth boy or dress in Brotherhood-branded gear like power armor and infiltrate the airship with persuasive conversation.
Once you've made your way to the upper section, plant the explosives. All the key points are along a single catwalk.
With the bombs planted, escape in the Vertibird and enjoy the fireworks. Use the minigun to take out the Brotherhood survivors on the ground. Speak to Desdemona at Railroad HQ to complete the quest.