score:8
For domestic flights, airlines may set their own ID policy. Air Europa's is here. For third country nationals, they state one of the following documents is required:
- Valid, non-expired passport or travel document
- Valid residence permit from Spain or a Schengen Country
- Driving licence (1)
- Visa according to nationality.
(1) A driving licence is only valid for domestic flights within the country issuing the document.
For Spanish nationals, they state the following documents are permitted:
- Valid ID or Passport (can be expired)
- Valid residence permit from Spain or a Schengen Country
- Driving licence (1)
Since you have an expired Spanish passport I believe you will be permitted to fly.