If you are flying at FL 330 and your Grid MORA is FL220 and your drift down is FL180. What would you do? You have an engine failure.
What is your minimum en-route altitude? If that is, temperature corrected, less than 18,000' you shouldn't be there in the first place. If it's less but you are off-route, go back to the route. But Flyburg has got the real nasty one - the Emergency Descent. Sod the engine failure case, that's not limiting. The big questions are where will you go and low will you go? And how long will you be above 10,000 if you have a pressurisation failure? If you have to push it, a sustained period of 14,000' might be acceptable but you shouldn't plan to put yourself in the position where you have no way out.
PM