Is a traveler's prayer valid on an airplane if he prays without knowing the direction of the Qiblah, and there is no one available to determine its direction for him?

A traveler on an airplane may perform supererogatory (nafl) prayers facing any direction, without needing to face the Qiblah, following the example of the Prophet (peace be upon him). As for obligatory (fard) prayers, it is necessary to face the Qiblah and to perform bowing (ruku') and prostration (sujud (definition)) if possible. If the time for an obligatory prayer comes while on the plane and it is possible to combine it with another prayer, then he should delay it to combine it with the subsequent prayer. He must ask about the direction of the Qiblah; otherwise, his prayer is not valid.