I saw your report and I had tested this with my previous version 14.04 to no avail. It appears that in the new version 15.04 this option added to GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub does enable the airplane mode button but the brightness controls still remain inactive (including using acpi_listen). Thank you for your suggestion though!
I saw your report and I had tested this with my previous version 14.04 to no avail. It appears that in the new version 15.04 this option added to GRUB_CMDLINE_ LINUX_DEFAULT in /etc/default/grub does enable the airplane mode button but the brightness controls still remain inactive (including using acpi_listen). Thank you for your suggestion though!