1. How will one calculate the
salaah time if one is travelling on plane and which salaah time should be
followed ?

2. If one
boarded before Esha n wants to read Esha on the plane which times  place
he should follow if  its fajr at the time the plane is passing over a
another country? 

Answer: 

1. Every Salah should be performed at its stipulated time of that specific area that a person is flying over while travelling.

Allah Ta'aala says in the Holy Quran:

إِنَّ الصَّلَاةَ كَانَتْ عَلَى الْمُؤْمِنِينَ كِتَابًً مَوْقُوتً

Indeed Salah has been made obligatory for the Mu’mineen at fixed hours (therefore, cannot be brought forward or delayed from its time).4:103

2. The Salah-time of the region where the plane is flying will be taken into consideration with regards to Salah as cited above. In the enquired case where you boarded before Esha and desire to perform your Esha Salah in the plane; however, it is Fajr-time in that particular area where the plane is flying, you will be obliged to perform your Esha & Witr Salah before performing the Fajr Salah if you are Sahib ut Tarteeb (a person who has not missed six obligatory prayers or more and there is 1. enough time to perform the missed Salah and the present Salah, and 2. you remember that you have less than six missed prayers); otherwise, you may perform the Fajr Salah for now and make up for your missed Salah afterwards as soon as possible. (Nurul Idaah Pg. 147-148) 

Nonetheless, you may use a beneficial program (https://www.halaltrip.com/) which aids in determining the Salah timings in flights.

Note: The above-mentioned ruling is with regards to the normal circumstances; however, in higher latitude locations, twilight may persist throughout the night during summer (some European and north American countries), for these periods, it is not possible to determine the Fajr & Esha timings using the standard calculation methods; so, the ruling will differ.

AND ALLAH TA'AALA ALONE IN HIS INFINITE KNOWLEDGE KNOWS BEST

ANSWERED BY: MOHSIN KHAN 

CHECKED AND APPROVED BY: Mufti Muhammed Saeed Motara Saheb D.B. 

Islamic Date: ٨ صفر ١٤٤١ 

English Date: 06 November 2019