The Halakhot of Davening on an Airplane

Gil has a great post about prayer in the friendly skies. As is usual with Rabbi Student, his post is a serious social and religious critique against the mindset of certain individuals and groups of individuals, but formulated as a “dry” halakha shiur. That’s what makes his blog so much more effective than simply ranting about the nincompoops blocking access to the bathrooms and waking everybody up (which is probably what I would do).

The topic reminded me of a question that I had regarding zmanei tefillah on airplanes. Clearly (according to the overwhelming majority of poskim), objective events such as sunrise and sunset are calculated based on when the sun actually rises and actually sets where you are. What about calculating the hours (sha’ot zmani’ot)? Do you base it on the calculation of hours on the ground below you, or on the projected time of sunset?

To give a concrete example of the ramifications of this question, consider the following:

I am flying east from NY to Israel on a flight that left JFK at around 3pm and will land in Israel at around 9am. Sunset in Israel is at 7pm. The sun rose on the plane about an hour before landing. By the time I would get a chance to daven, it will be 10:30 – after sof zman tefilla in Israel. So perhaps I should daven on the plane.

However, I can make the following calculation. Since I was flying east, I lost some daylight hours. I will have a total of 11 hours of daylight which began at 8am Israel time. Using those figures, sof zman tefilla comes out to be just before noon, and I will have time to daven after collecting my belongings.

The same type of calculation can come into play in a number of ways, with real halakhic ramifications. The question is a fundamental one, though: are zmanim calculated based on geographical realities or human realities? Is it about the place or the person?

Anyone address this?
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