When should I abstain from food to begin fasting on September 26th, considering that I will break my fast at a Chinese airport and arrive in Egypt at dawn the following day? And will sunrise aboard the plane affect the time of imsak (abstention)?

A traveler begins and ends their fast according to their current location. If the plane departs after sunset, the traveler breaks their fast at the airport or in the country they are in at the time of sunset. If dawn breaks while they are on the plane, they must abstain from food and drink at dawn while on the plane. The determining factor is the sunrise and sunset in the place where they are. If the traveler wishes to break their fast during travel and make up for it after Ramadan (definition), they are permitted to do so, based on the Almighty's saying: "But whoever among you is ill or on a journey [during them] - then [he must fast] an equal number of days [of other days]." (Al-Baqarah:184).