Just as an FYI, you can easily fly from Madrid Barajas (MAD) to many Camino starting spots, including: Sevilla (VdLP) (SVQ), Pamplona, CF (PNL), Bilbao (CdN) (BIO), and Asturias / Oviedo (OVO) (C/Primitivo). You can also fly to Porto (OPO) to start the Camino Portuguese from there. If you fly on Iberia or one of their codeshare partners, your arriving and departing flight is from Terminal 4 at MAD
When I start at Saint Jean Pied de Port (SJPdP), I fly into Paris (CDG) and take the shuttle buses from baggage reclaim at CDG to Gare Montparnasse. See this link:
https://www.lebusdirect.com/en/lines-and-schedules/cdg-airport-paris-gare-montparnasse-line.html
From there, I take the TGV (high speed train) and TER #62. the light rail regional train from Bayonne to SJPdP. For me, coming from the east coast of the US, that works well. I always plan two nights on the front end of any Camino starting from SJPdP.
However, for any route starting in Portugal or Spain I have found it efficient to fly AA/Iberia into Terminal 4 at MAD. This includes their 'One World' codeshare partners. Connections are as easy and smooth as you will likely find anywhere, and in the same terminal. From there, it is an easy 1 - 2 flying hours to anywhere in Spain or Portugal.
This saves some time. The airline also transfers your checked baggage to your final destination. As this is the EU, you clear passport control at Madrid, but customs controls at your final destination. For me, thus has become my default routine. Also, I plan two nights at my 'jump-off' spot before I start my Camino.
Also, when I return to fly to Santiago de Compostela (SCQ) direct for my volunteer stints at the Pilgrim Office, I use the same routing: MIA > MAD > SCQ. It removes all the stress and anxiety on the first day.
Also (added later) you can use the "Open Jaw" flight concept. Using this, you fly into one city, say Paris, to get to SJPdP. You end up at Santiago, then fly home from there, via Madrid. The Open Jaw is the leg of this geographical triangle that you did not fly, but used some other method to travel (bus, train and foot). There is no law that says you must land and depart from the same airport. It usually does not cost more to do this either. But, it DOES help if you are using the same airline...
Hope this helps.