So Liam added an update with this explanation:
- Added Hanger slowdown feature for Lord Trilobite maps

And I thought I'd elaborate, because this might be a useful feature for other mappers as well.

The idea is that there is a trigger volume in a map that when a ship flies near it, the ship is slowed down. When you are flying a ship and get near one such trigger, the ships speed is capped to 20%. Once you move out of the range of the trigger, the speed cap is removed and you can fly at full speed again.
These triggers can be used for areas such as hangars and small spaces to prevent players from flying into walls really fast, because not everyone is a a great pilot. So it can be used as an aid to help people fly into cramped areas without hitting anything.

I have already implemented these triggers into my rp_stardestroyer map so that people are slowed down in the hangars. But I thought other mappers might want to use this feature on their own maps as well. So here's how you add it to your map...

Instructions:
In the Hammer editor, simply make a new brush in the area you want ships to slow down in. Apply the tools/toolstrigger texture to the brush and make it into a trigger_multiple.
Then set the name of this trigger to "ship_speed" and you're done! Now when ships fly near this trigger they will be slowed down to 20% speed. Note that the ships will be slowed down when they are near the trigger, not when they enter it. So you may want to test out how big you want the slowing down area to be, and see what works best.