Fallout 4

Occurring after the Brotherhood of Steel's attack on the Railroad in Precipice of War and the Railroad's attack on Cambridge Police Station, you, Tinker Tom, and Deacon will now be ready to sabotage the Brotherhood Airship.

On the flight, it is mostly simple with banter between Tinker Tom and Deacon and some nifty Vertibird flying. Eventually, docking will occur.

From this point there are three options for accomplishing the task:

Infiltration
Deacon gives the Sole Survivor a BOS uniform prior to boarding the vertibird. If worn when landing, the inhabitants of the Prydwen will not be hostile on arrival, however if the player character encounters any leaders of the Brotherhood they will challenge the player character's purpose. This requires the player character to pass difficult dialogue persuasion checks to avoid turning the Brotherhood NPCs hostile. There is also a "double infiltration with Deacon" technique. If Deacon is the player character's companion he will not give them the BoS uniform, but will instead wear it himself as a disguise and will sit in a different part of the Vertibird. If the player character has both Deacon as a companion and equips a BoS uniform before boarding the Vertibird, then Deacon will participate in the infiltration on the Prydwen. At least one BoS uniform should be available inside the police station or the front approach. Deacon reacts favorably to ("loves") most of the choices during the first persuasion check on the Prydwen. This is the most peaceful option and can be completed without taking any damage whatsoever. However, with this method the player character will never encounter Elder Maxson and therefore cannot obtain Maxson's battlecoat or Final Judgment.

Stealth
It is theoretically possible to sneak all the way through the Prydwen without being challenged or directly attacked, though the Brotherhood NPCs will still become hostile at some point during the mission.

Assault
If the Brotherhood uniform is not worn, all Brotherhood personnel in the area will immediately be hostile after disembarking from the Vertibird and throughout the mission.

Brotherhood personnel will be armed with laser weaponry. There will also be several adversaries wearing Brotherhood T-60 power armor.

If the player character is not using the Brotherhood uniform, there will be a large amount of incoming fire at the start since the Brotherhood personnel on the ground will also open fire along with the people on the flight deck. There is usually at least one knight in power armor on the flight deck as well.

Go through the door at the end of the deck to enter the command deck. There will be less NPCs here and none in power armor. With a careful approach it may be possible to eliminate/avoid all of them without alerting them to the Sole Survivor's presence. The next target is a ladder/hatch to the main deck.

There is a power armored guard at the top of the ladder who will have to be dealt with almost immediately if the NPCs are hostile. This section of the Prydwen has the bulk of the Brotherhood personnel, so if they are hostile toward the player character there will be a lot of incoming fire and at least three power armored opponents. If the player character is infiltrating and their cover is not blown, this is also the most likely place to encounter NPCs that will interrogate them about their purpose. If the player character fights their way in or out, it will result in the deaths of several prominent Brotherhood NPCs.

In either case, the player character needs to make their way up two levels by using the stairways at the sides of the catwalks. The third level should be a central walkway that goes between three large oval structures. These are the gas bags. Each one has a red operating console in the center on the port side of the railing. Walking up and activating each one will set the explosive charges.

Once one has placed the charges, they can choose to continue with the undercover operation and exit the Prydwen without hostilities if they succeeded in avoiding detection or raising insurmountable suspicions by any Brotherhood NPCs. If the Brotherhood turns hostile, then one must run or fight their way back to the hatch to the command deck. If the Brotherhood has turned hostile then, unless he was somehow encountered elsewhere, when the player character emerges onto the command deck, Elder Maxson, if not killed earlier in the game, will be waiting along with some other opponents. He will be armed with Final Judgment and may have others with him using Gatling lasers. Proceed to the flight deck.

No new NPCs should have spawned on the flight deck if they were eliminated earlier, however if the player character snuck in, then they will now be hostile. Fight, sneak or run past them to the Vertibird. Once the player character activates the option to get onto the Vertibird, Tinker Tom will begin taking off. More NPCs will spawn on the ground at this point and the amount of incoming fire will increase by quite a bit. The Vertibird cannot be shot down but the player character can still take damage from the incoming fire.

After the Vertibird undocks and flies away for a minute or so, Tinker Tom will announce that they are far enough away and will ignite the charges. The resulting detonation should eliminate all remaining hostile Brotherhood NPCs from the area. Tinker Tom will fly to the area of Nordhagen Beach and tell the player character to disembark so he can stash the Vertibird.

Finishing the quest requires speaking to Desdemona, who has returned to Railroad HQ. Once the Sole Survivor speaks with her, The Nuclear Option will begin.

(Taken from Nukapedia the Fallout Wiki)