The Miqat boundaries (designated entry points for احرام) apply whether you travel by land or air — passing them without being in احرام when you intend حج or عمرہ is not permitted. Since modern flights are fast, preparation is key. The practical approach is to perform غسل (ritual bathing) and grooming at home or the departure airport, then change into your احرام garments either before boarding or in the airplane lavatory before the Miqat is reached.
Most airlines operating حج and عمرہ flights announce when the plane is approaching the Miqat boundary. If your airline does not make this announcement, use a GPS-based Miqat alert app (احرامOS includes this feature) or research your flight path to estimate the timing. Common Miqat points for air travelers include: Dhat Irq for those coming from the east, Yalamlam for those from the south, and Al-Juhfah for those from the north and west.
Once you are in your احرام garments and approaching the Miqat, make your intention (niyyah) in your heart — specifying whether you are performing حج, عمرہ, or both — and begin reciting the تلبیہ: 'Labbayk Allahumma labbayk...' If you realize you have passed the Miqat without entering احرام, the majority of scholars say you must either return to the Miqat (if possible) or pay a fidyah (sacrifice a sheep in مکہ مکرمہ). To avoid this situation, it is safest to enter احرام well before the estimated Miqat crossing.