MD-80 case
SR 111 wasn't the only Swissair smoke case. They lost a Coronado due to smoke - caused by a terrorist bomb in the baggage compartment - leading to complete loss of visibility within the cockpit. The aircraft crashed with all souls.
Also there was an MD-80 which developed smoke in the cockpit as a result of a faulty Emer Pwr switch - here also the CB (main battery CB - 80 Amperes!) which was in the underfloor compartment did not pop.
The initial press reports seemed fairly routine but in fact the slight puffs of smoke rapidly developed into black clouds with irritating dust and debris in it. The only instrument items which could be made out were the self illuminating digital frequency setting windows.
The crew quickly decided to return to MUC - which was a tick closer than ZRH and managed a straight in approach to 08 with the greatest of difficulty - the non flying pilot using the (unreadable) checklist as a fan to clear some of the smoke. The Approach controler had to be asked for the ILS frequency and course as the charts could not be read.
On this occasion the aircraft was evacuated on the runway. Only then could the captain see, that the windshields and instruments were covered in a thick dust, as were his smoke goggles.
The smoke removal checklistlater had to be completely revised and thickly printed - on the rear cover. It could not be read and the crew had attempted to carry out the actions from memory. They thought that they had opened the cabin pressurisation wheel fully (they could only feel it) but in fact it was only about half open and the cabin never did depressurise to the point where they could have opened a window.
The Emer Pwr switch was in such a state, that in all probability a minute or two under power would have led to a fire. The RTB was a good call.