Asr and Maghrib Salah whilst travelling on the plane?
In the name of Allah, the most Beneficent, the most Merciful.
There are differences of opinions with regards to the ending of Zuhr salah and the beginning of Asr Salah. Imam Shafi (RA), Imam Malik RA) and the majority of scholars have said that the Zuhr salah ends at Mithl Awal (when the length of the shadow of the sun is equivalent to your height) and after that Asr salah starts. Imam Abu Hanifah (RA) has narrated a few opinions. One opinion is similar to that of Imam Shafi and Imam Malik (RA). Furthermore, Imam Abu Yusuf and Imam Muhammed (RA) also act upon this opinion. The second opinion is that Zuhr salah remains until Mithlayn (When the length of the shadow becomes twice your height) and after that Asr salah starts. This is the most common opinion and the Fatwa in the Hanafi Fiqh is given on this opinion. The third opinion is that the time between Mithl Awal and Mithlayn includes both the time for Zuhr prayer and Asr prayer. This opinion can be acted upon by travellers who are permitted to read their Asr prayer at Mithl Awal. (Dars Tirmizi p.395 v.1)
With regards to salah on an aeroplane, it is an issue where there are different opinions regarding its validity. It is therefore, best one does not perform ones salah one board if one feels that he will be able to perform his salah when the plane lands. If that is not possible or there is a danger that the salah may become qadha then one can pray the salah on board the plane. However, it should be borne in mind that it is incumbent in that situation to pray salah standing, performing the ruku and sajdah properly facing towards the qiblah. If any one of these three conditions are missing one will be obliged to repeat the salah again. (Imdadul Fatawa p.587 v.1 & Fatawa Darul Uloom Deoband p.156 v.2)
Finally, it should be borne in mind that any salah performed sitting on a seat even though they are able to perform salah standing would be considered invalid. One would have to repeat the salah again. (Fatawa Mahmoodiyah p.229 v.14 & Imdadul Fatawa p.568 v.1)
Regarding your question, you should pray your Maghrib Salah on the plane at the Maghrib time of your intended destination. (Ahsanul Fatawa p.71 v.4)
Only Allah Knows Best
Mohammed Tosir Miah
Darul Ifta Birmingham