Well, if you are thinking it going to go touch the moon and get back, you are right.
I mean, you are right about helping yourself to reading this answer.
So, lets assume:
The pilot goes crazy, and decides to ascend vertically with full throttles open.
Now, the engines might support the vertical flight up to a few seconds assuming the plane was flying way faster than its stalling speed, but only for a few seconds.
This is what might happen to a flight travelling at .6 mach at 38,000 feet when the pilot suddenly decides to ascend vertically.
- The Engine Stalls soon enough since it is not meant for such output and the pilot loses complete control of the aircraft soon enough.
- The Engine & the Airframe of a passenger plane is not built to take such aerodynamic loads. The Airframe may soon give away if engine does not stall and aircraft continues climb.
- At higher levels of the atmosphere, icing on the wings may lead to ‘no generation of lift’, which is again fatal.
A passenger aircraft is not meant to go against the gravity at such destructive angles of climb.
The systems will not allow the pilot to vertically ascend in the first place. Even if the pilot overrides the system, it is a disaster waiting to happen.
If the airplane is going perfectly straight up (nose pointed almost vertically), it will eventually stop going up, as thrust will be less than the weight of the airplane. This would happen to any airplane with an air-breathing engine eventually, as thrust decreases with altitude.
The plane would stop for moment, then begin descending backwards. Note that this is not a stall. The aerodynamic forces exerted on the plane when going backwards would attempt to flip the airplane around so it’s going nose-first again. If the pilot is very lucky, the airplane would end up in a very steep dive and would be flying aerodynamically again. If the pilot is unlucky, the airplane would be flipping about all 3 axes almost randomly, and would be ripped apart in a few seconds.
In this scenario, you don’t even have the minimal consistency of a proper stall or spin