In the Name of Allah, Most Gracious, Most Merciful.
All praise and thanks are due to Allah, and peace and blessings be upon His Messenger.
In this fatwa:
In his response to your question, Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
The standard view among scholars is that air travelers should assume ihram before landing in Jeddah as they will fly over the miqat before landing. I would advise you to choose this option – should it not pose a problem for you.
If, however, you are coming from a European country or North America directly, you may experience difficulties. If you are in the last category, then you may follow the ruling of some eminent scholars who consider Jeddah as a miqat for air travelers. Their reasoning is that while flying you are not in fact passing through the miqat.
The Prophet (peace be upon him) set the example for us to show that by miqat he meant a station for the pilgrims to halt and recuperate and make the preparations before embarking on Ihram.
During the Prophet’s Hajj (the only Hajj he performed), when he travelled from Madinah for Hajj, he halted at Dhul Hulayfah and spent the night there. It was on the next day he entered the state of ihram after the preparations such has bathing and changing into ihram attire, etc.
None of the above applies to those who are flying over the miqat, for a flight does not touch the ground; it takes only minutes for the plane to fly over the miqat. Therefore, the reasoning of these scholars seems to be reasonable and in line with the purposes of the Law-Giver.
In conclusion, if assuming ihram before boarding the plane or in the plane poses difficulties for you you may do it in Jeddah by following the ruling of the second opinion.
I pray to Allah to bless your journey and grant you a virtuous Umrah.
Almighty Allah knows best.