Sennheiser HD590 on an airline flight?

I assume that you are posing this question because the HD590 is an open-back design, which makes the sound from the headphones audible to someone sitting next to you. As a general proposition, I don't think this will be a concern as the cabin noise will drown out most of the output from the headphones. I often use my Sennheiser HD600 headphones on airplane flights, playing them through the Sennheiser DSP 360 unit. I keep the volume at a reasonable level, and have never had anyone next to me complain.

Husk01: the Sennheiser DSP 360 is a small amplifier / digital signal processing unit. It has RCA inputs for CD players, etc., and a mini-jack for output to headphones. The "DSP" feature creates the sense of a nearly 360 wrap-around sound (this technology was originally developed for use in combat aircraft). Although the DSP 360 does not offer noise cancellation (which can be very enjoyable on long plane flights), I have found it to work well anyway. The DSP 360 retails for about $150, but I bought mine on sale for $49 from The Audio Advisor about a year ago.