When having an elytra equipped and taking damage, the elytra looses durability. When reaching 0 durability, the elytra item gets destroyed.

How to reproduce

1. Get an almost destroyed elytra:

   /give @s minecraft:elytra[damage=420]
   

2. Equip the elytra
3. Get damaged
4. Notice that the elytra is getting damaged
5. Get damaged more so the elytra reaches 0 durability
6. The elytra item gets deleted

Expected result

An elytra should only loose durability when flying and should never get below 1 durability.