So as a passenger in the back - if we're taxing to the runway and the flaps aren't extended - do I notify the F/A?
There's that bit of hesitation that everything is normal and you're just a passenger - so what do you know?
But after spending a lot of time on planes and usually sitting in the exit row, if not upfront, I tend to make a note of the flap/slat extension after-start and provide an extra verification before my flight takes off
Would you like to crosscheck the weight and balance too? Just kiddin'.
There may be reasons the aircraft taxies to the rwy without flaps. For instance, if there is snow or slush on the taxiway some SOP's say leave the flaps in till at the runway. Or maybe the aircraft will be de-iced at a remote station.
Having said that, you have a point. I don't think there is a pilot here in the room that will not have a strong urge to shout something when they see the flaps are not set at all approaching the runway. Maybe the will then shrug it of thinking 'there goes the config warning'...
I have twice told the crew about something I thougt was wrong, both times I was wrong, but better safe than sorry. The other way around we've had a passenger telling us AFTER the flight that one of our speedbrake panels was fluttering. Of course we shrugged it off, but called for an engineer anyway just to be sure, who subsequently found a major rupture in the panel's hydraulic actuator, grounding the plane for the rest of the day. NOW I wish that pax had spoken up in flight! Of course you understand that it is a delicate balance. There would be a problem if passengers loose trust in the crew and start taking ACTION, like opening emergency exits the moment they think something is wrong (countless times on every flight). It might occasionally save one aircraft, but it would endanger thousands of other flights. But sure, if you think something is really wrong, think about it for a second and then speak up.