How to land the aircraft when the flight deck is full of smoke?
Smoke is a real challenge on an aircraft. The first course of action, other than extinguishing the source of the smoke, if possible, is to evacuate the smoke. In some aircraft windows can be opened. Some have a system to vent the smoke outside. In the crash of SAA flight 295 it was mentioned that the smoke evacuation procedure on the 747 Combi was to open the entry door in flight.

When UPS Flight 6 had an onboard fire the smoke evacuation system was inadequate and the pilots were unable to land safely. They were unable to see any of the instruments or the runway. It ended in disaster. Many lessons were learned from it and advances were made to help deal with smoke in the cockpit.

There are three distinct problems with smoke:


Smoke inhalation Having an adequate supply of breathable air or oxygen is key. On UPS 6 the captain's oxygen supply ran out. He attempted to get to another mask, but succumbed to smoke inhalation before he could get there. There can still be plenty of oxygen in smoke-filled air, but smoke contains many toxins that quickly damage the lungs making it impossible to get the oxygen into the blood. Some toxins damage the hemoglobin in the blood so that it can't pass oxygen to tissues. Some types of material can even produce cyanide when burning.
Eye irritation. I was in a house fire once and I can tell you that my biggest problem was the eye irritants in the smoke. Even a moderate amount of smoke contains enough irritants to be debilitating. The smoke in my house was nowhere near being thick enough to prevent seeing through it but my eyes teared up and there was an almost irresistible reflex for them to close. It's very painful and it takes a lot of effort to keep them even partly open. Finding the fire extinguisher was a difficult task. One of the lessons learned from the UPS accident was that pilots needed to have protection for their eyes also. The best solution is to have full face oxygen masks similar to what firefighters wear.
Opacity Since a cockpit is enclosed, if smoke builds up faster than it can be evacuated then it can become thick enough to prevent seeing through it. I've read stories of pilots of light aircraft actually sticking their head out the window to land. Seeing instruments is also a problem. One development made in the wake of UPS 6 is the Inflatable Vision Unit. This is a transparent inflatable bag that fills up with clear air and displaces thick smoke to allow pilots to see instruments and out the window. 

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I'm not sure how many aircraft are equipped with such a system, but combined with oxygen and eye protection it could make a big difference in a severe smoke situation. (As was apparently experienced by Santa this Christmas Eve!)