All perfect praise be to Allah. Blessings and peace be upon Prophet Mohammad and upon his family and righteous companions.
It is imperative that the Hajj, or Umrah pilgrim doesn`t pass the Miqat ( place of assuming Ihram) without assuming Ihram ( ritual consecration ). Ibn Abbass narrated: “Allah's Apostle (PBUH) made Dhul-Hulaifa as the Miqat for the people of Medina; Al-Juhfa for the people of Sham; Qarn-al-Manazil for the people of Najd; and Yalamlam for the people of Yemen; and these Mawaqit are for the people at those very places, and besides them for those who come through those places with the intention of performing Hajj and 'Umra; and whoever is living within these boundaries can assume lhram from the place he starts, and the people of Mecca can assume Ihram from Mecca.” {Bukhari&Muslim}.
Therefore, assuming Ihram from the city of Jeddah isn`t permissible since it is within the Miqat, but it is permissible for the Hajj, or Umrah pilgrim to wear the clothes of Ihram at home, or on the plane, and to make the intention of Ihram when reaching a place parallel to the Miqat which will be indicated by the pilot, or the guide. And Allah knows best.
