As salam wa Alikum , sheikh Can I pray Dhuhr and Asr together at home before going to the airport, knowing that Asr is at 6:00 PM and the flight departs at 5:45 PM? Or do I have to pray Asr separately at its time

Ustadh AbdulAziz al-Haqqan

If you won't arrive until maghrb time has entered and you can't pray in the airplane, then yes you can combine, but without shortening the salah.