An MD11 Captain turned off an IRU in flight when he intended to open the flight station door because the switches are located very close to each other on the overhead panel.

Narrative

After level off at initial cruise altitude; the Relief Flight Officer entered the proper code to request entry to the flight deck. The Captain reached up to disarm the FDAS door lock; and inadvertently rotated the switch for the number 2 inertial reference unit (IRU) to the off position. We referred to the Quick Reference Handbook (QRH); which directed the First Officer to select use of the aux IRU for his flight and navigation inputs. We also consulted the QRH to ensure that we still had the requisite navigation equipment to continue our flight. The flight continued to destination with no incident. This is certainly not the first time that a pilot in the left seat has accidentally turned off an IRU while intending to release the lock on the FDAS. While the switches of the two systems are somewhat different in shape; they are located within inches of each other on the overhead panel. This co-location of the switches; plus the lack of a guard over the IRU switches; poses an on-going risk of a repetition of this event. Suggestions for avoiding this event in the future could include: Always look up at exactly where your hand is going before changing a switch position. Move location of either FDAS or IRU switches so they are not co-located. Install switch guards over the IRU switches so that they cannot be inadvertently repositioned once the IRUs are initialized during preflight.