In this comment I pondered if I should ask:
"Did Test pilot and astronaut Joseph A. Walker see stars during the day when flying the X-15 above the Karman line?
But instead, I'll just ask at what altitude might a pilot be able to see at least the brightest stars during the day?
Assume cockpit lights and panel illumination are dim-able and a high tech high altitude aircraft (e.g. the X-15 or something modern or near-future) is used.
I don't think it's easy to see bright stars during the day at cruise altitude by eye without some help, but at some altitude it should be.
Is there any information on what altitude this might be?