How to safely transport a Brompton by air?
Flying with a Brompton [as a carryon] is typically dependent on the airport staff and flight crew, rather than airline policies and procedures. I've had success getting the bike on larger planes no problem, mostly because overhead compartments were very large, or because there was sufficient space to store the folded bike (with seat and pedals removed) with strollers and folded wheelchairs. I'll even refer to it as a "mobility device", which will sometimes spook TSA into thinking that they're denying me accessibility or civil rights.

Again, this is mostly dependent on the gate/flight crew's level of tolerance/patience. The easier you make the process for them, the more likely they are to let you take the bike on the plane. 

Here is a good blog post about the process itself.

A second, great blog post with tips as well.

Technically speaking, here are a few tips:


I use "Superior" MKS pedals that are completely removable. Nothing sticking out of the bike; they go into a separate bag in luggage.
I'll typically put a small bungee cord around the bike (inside the bag) to keep the bike from rattling/moving too much. It's also much more stable when being handled by flight crew/TSA.
Remove the seat; put it in your luggage/carry-on.
I also deflate the tires a little. This helps when the luggage compartment is a tight fit, and let's the tire sticking out give a little when the latch is shut.


Generally, the bike has suffered no real damage when I've carried it on or gate-checked it.