This paper is a pretty good start:

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/224437/pb13988-emission-factor-methodology-130719.pdf

Dear John,

Thank you very much for the report.

It is a very useful resource.

Kind regards,

Mohammed

Article Carbon dioxide emissions from international air freight

Article Assessment of carbon emission costs for air cargo transportation

you may also check these

Dear Iftakharul,

Thank you very much for your reply. I will check and I think these resources are more appropriate for what I am looking for.

Kind regards ,

Mohammed