what are the rules/conditions Mr Boeing evaluate in order to write on the QRH 'Plan to land at the nearest suitable airport'
That's a good question!
Those are the checklists that lead you to a 'Plan to land at the nearest suitable airport'
WINDOW DAMAGE
CABIN TEMPERATURE
PACK L+R
Eng Lim/Surge/Stall
Eng Svr Damage/Sep
ENG FAIL
ENG OIL FILTER
ENG OIL PRESS
ENG OIL TEMP
Vulcanic ash
FIRE APU
FIRE ENG
Smoke fire or fumes
FIRE CARGO
FIRE WHELL WELL
OVERHEAT ENG
SMOKE EQUIP COOLING
SMOKE REST UPR DR
FLIGHT CONTROLS
FUEL LEAK
FUEL QTY LOW
HYD PRESS SYS L+C
HYD PRESS SYS R+C
HYD QTY LOW L+C+R (any of the combination with C)
TAIL STRIKE
It isn't mention in a Dual Eng Fail but ... common sense!
From one point of view, it looks like the logic is fire or smoke, hydraulic, pressurization (only tail strike and both packs), fuel, partial loss of thrust! Nothing new since beginning!