This idea is inspired by, and is a more practical alternative to "Airplane Controls overlay" See link.
Device: A keypad + Laser pointer combination.
The Keypad electronics knows each item's position by the number. The person on the tower has to just give out the number of the item..
the person trying to land the plane can just key it in and the laser pointer fit on the wall behing the pilots does it's job of pointing it.
The Keypad + Laser can be powered from the plane , though will carry a small battery pack just in case. except for that part, the system is completely independant from the rest of the electronics on the plane.
The beauty of the idea is that it is quick. The number can come from a multitude of sources. The following list is ordered in a descending fashion of quickness.
1. The person on the tower can look up item numbers on a computer screen by moving the mouse cursor over the corresponding part on an image of the cockpit.
2. The person on the tower can look up the numbers on a large sheet where the numbers are overlayed on the image of the cockpit, which is kept as a backup if the computer goes down. This is still quicker than the next method because the guy in the tower knows the cockpit well.
3. The emergency manual in the cockpit can mention the number of the item every time it is mentioned in the book.
4. There can also be a complete index (both digital and printed) of items against their numbers, if the person is getting instructions from someone who does not have access to the numbers.