Smoke - I always assume it will originate from an uncontrollable fire. So even though the aircraft I fly has no recall items for air conditioning / electrical smoke or smoke of unknown origin, it's masks on, establish comm, declare MAYDAY, sq. 7700, initiate emergency diversion, liaise with cabin - and then take the QRH.
If the QRH solves the situation 60 sec. later, then we're not considerably worse off than we were 60 sec. earlier. But 180 sec. better off than if we'd be if we had done the entire QRH in the cruise and it hadn't solved the problem
Swissair 111 taught us some valuable lessons - and I abhor TRI/Es who treat the smoke drill in the sim as a QRH-reading drill. It's a CRM drill and should be treated as such - it makes for a great and simple LOFT-exercise, since you can let the crew deal with it in several ways, all of wich can lead to satisfactory outcomes (of course depending on what type of failure the exercise is built around
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