Assistance dogs (training documents) 

Only ADI / IGDF 

KM Malta
Ryanair
Aer Lingus
Brussels Airlines 

Only ADI / IGDF + document
of carrier’s country of origin  

Luxair (ADI + IGDF + Luxemburguish document)
Vueling (accrediting organisation such as ADI, IGDF or ONCE)
TAP (ADI + IGDF+ national certification) 

Other 

KLM (ADI + IGDF + comparable organization)
Lufthansa (ADI + IGDF + recognised training institute)
Eurowings (ADI + IGDF + training facility)
LOT (certificate by reputable training institute)
Air Baltic (ADI + IGDF + Latvian and German official document + EGDF)
Sky Express (ADI + IGDF + National Documents + EGDF)
Air France (training certification)
Wizzair (document proving dog is certified assistance dog)
Cyprus Air (certificate confirming training)
Aegean (ADI + IGDF + EGDF + national certified school)
Finnair (certificate of training)
SAS (card or document by training organisation)
Easy jet (ADI + IGDF or other organisations with comparable standards)2
Austria Airlines (Messerli Institute + ADI + IGDF + other)
ITA Airways (training certificate)
TAROM (document that prove animal qualification)
Smart Wings (certificate that the dog is trained)
Iberia (ADI + IGDF + Spanish Document + other)
Transavia (ADI + IGDF + IAA Quality Registry) 

No information 

Nyxair
Braathens (does not carry assistance dogs)
Bulgaria Air
Croatia Airlines (does not require any specific document)