When traveling by plane, many things change drastically. One of the things faced by many Muslim travelers is the issue of Salah.
It is obvious that the planes do not provide the convenience that one enjoys while on the ground and that certainly makes observing Salah difficult. Furthermore, if one has to perform ablution, the restrooms are certainly not designed to be used for washing feet etc...
This only adds to the difficulties of the Muslim passenger.
However, Shariah does take these extraordinary circumstances into consideration and realxes its rulings to a great extent.
Therefore, one should carefully examine the number and timings of each prayer that will occur during flight.
One may offer Salah aboard an airplane. Although, it is preferred to delay the Salah until the plane lands provided that enough time remains for that particular Salah.
If one knows with certainty, the time will expire before landing then one should offer the Salah aboard the plane.
Under normal circumstances, one will be required to perform Salah as it is performed regularly i.e.. Qiyam, Ruku, Sujood etc...
However, if one finds it difficult to stand due to the turbulance or instability during flight then one may offer it sitting.
If it becomes impossible for one to offer Salah in its normal form during flight due to space issue then one may offer the Salah while sitting in his/her seat and should also repeat the same Salah later upon reaching the ground.
Similarly, if one does not find water or finds it extremely difficult to perform ablution then one may observe Tayammum if possible.
If someone can not do both ablution and Tayammum then such a person is called "Faqidut-Tahurain" i.e... one who is missing both water and sand. In which case, one may only immitate those who perform Salah and later he/she should observe the Salah when conditions are back to normal.
If someone is performing Salah while standing during flight and suddenly experiences turbulance then he/she may sit down and offer the remaining Salah sitting.
The direction of Qiblah may be determined by asking one of the flight attendants. However, if the direction of Qiblah can not be determined then one may offer Salah in any direction that he/she thinks is the direction of Qiblah which is known as "Taharri" in Fiqh.
And Allah knows best.
Mufti Ikram ul Haq
Fatwa Center of America
25 Dhul-Qa'dah 1431/ November 2 2010