With Helios, the only person who was still conscious tried (unsuccessfully) to fly the plane safely down
See what the post I replied to says... there is a risk of both pilots becoming incapacitated while some on here try to refute that point.
If there is a suitable airport nearby, diverting there without any further help would probably be the safest thing to do, but what about over the Atlantic with 2 hours to anything hard to put the landing gear on?
I read up on Helios. The F/A taking over the controls was even a CPL, but with no fuel left, he was out of options:
"At 11:49, flight attendant Andreas Prodromou entered the cockpit and sat down in the captain's seat, having remained conscious by using a portable oxygen supply.:139 Prodromou held a UK Commercial Pilot Licence,:27 but was not qualified to fly the Boeing 737. Crash investigators concluded that Prodromou's experience was insufficient for him to be able to gain control of the aircraft under the circumstances.:139 Prodromou waved at the F16s very briefly, but almost as soon as he entered the cockpit, the left engine flamed out due to fuel exhaustion:19 and the plane left the holding pattern and started to descend."
I’ll reiterate why I mentioned Helios for those who don’t understand why I used it as a example... in your original post, you mentioned about dual incapacitation. That’s a perfect example (pilots died due to asphyxiation and the CPL holding FA survived). Unfortunately the thing ran out of fuel as discussed above. Fredrik, you correctly pointed out that there is risk for both pilots to be incapacitated.
Actually another example is United 93. The passengers organized their effort to retake the plane and had a retired airline pilot willing to take over had they been successful in retaking control.
Overall, a 757 or 737 or whatever you want to fill in the blank with flies the same regardless of who’s paint is on the outside. Airlines have differences in day to day SOPs ( like when you do certain things). I know for example UA had a buffer speed that you’d have to be an x amount of KIAS below flap extension speed whereas other airlines don’t have that.
In an extreme case of total incapacitation, SOPs would not apply.
C172-M/N/P/R/S , PA-28-180, P2006T, PA-34-200T, B1900D, DH8A/C ERJ-145, CRJ-100/200, DH8D, CRJ-700/705/900, E-175/190, A319/320/321, 737-200/300/400/600/700/800/900ER/M8, MD-82/83, 757-200/300, 767-300, A330-300, 787-9, 777-300ER, F28-4000.