Titanfall 2 has 46 Pilot Helmets Collectible Locations. Finding all unlocks the "Every Nook and Cranny" Trophy / Achievement.

In Mission select you can see how many Collectibles you have found. Additionally, you can pause the game anytime and see a little collectible tracker in the bottom right. They all look like glowing Pilot Helmets and you must pick them up while on foot (not in your Titan). Once you find them they are saved instantly. You can quit out to the main menu immediately without losing any progress and you don't have to get them again if you die.
None of the Pilot Helmets are missable, they can be collected via mission select at any time.

There are 9 missions and they all contain at least one collectible.
You also get the trophies "Off the Beaten Path" for finding 10 Collectibles and "Collector" for finding 25 Collectibles.

TIMELINE:

#1 - The Pilot's Gauntlet - 0:05
#2 - BT-7274 - 0:37
#3 - BT-7274 - 0:53
#4 - Blood and Rust - 1:23
#5 - Blood and Rust - 2:06
#6 - Blood and Rust - 2:42
#7 - Blood and Rust - 3:07
#8 - Blood and Rust - 3:32
#9 - Blood and Rust - 4:04
#10 - Into the Abyss - 4:44
#11 - Into the Abyss - 5:20
#12 - Into the Abyss - 5:52
#13 - Into the Abyss - 6:33
#14 - Into the Abyss - 7:03
#15 - Into the Abyss - 7:28
#16 - Into the Abyss - 8:21
#17 - Into the Abyss - 8:49
#18 - Into the Abyss - 9:10
#19 - Effect and Cause - 9:36
#20 - Effect and Cause - 9:56
#21 - Effect and Cause - 10:21
#22 - Effect and Cause - 10:58
#23 - Effect and Cause - 11:35
#24 - Effect and Cause - 11:58
#25 - Effect and Cause - 12:15
#26 - Effect and Cause - 12:41
#27 - The Beacon - 12:56
#28 - The Beacon - 13:12
#29 - The Beacon - 13:54
#30 - The Beacon - 14:31
#31 - The Beacon - 14:52
#32 - The Beacon - 15:26
#33 - The Beacon - 16:01
#34 - The Beacon - 17:19
#35 - The Beacon - 17:58
#36 - The Beacon - 18:38
#37 - The Beacon - 19:14
#38 - Trial by Fire - 19:53
#39 - Trial by Fire - 20:17
#40 - Trial by Fire - 20:50
#41 - The Ark - 21:29
#42 - The Ark - 21:47
#43 - The Ark - 22:04
#44 - The Fold Weapon - 22:49
#45 - The Fold Weapon - 23:20
#46 - The Fold Weapon - 24:09

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