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In this comment it's mentioned that pilots in instrument conditions may wind up in a situation where they're inverted due to spatial disorientation, and be completely unaware of it until they fly out of the cloud.
Is that really something that can happen so easily?
The short answer is "Yes", if the pilot is not properly trained, doesn't trust their instruments, or has an instrumentation failure.
Without a visual reference (such as the real horizon or artificial horizon) it's very easy for a pilot to place their aircraft in an "unusual attitude" -- something other than the expected straight-and-level flight or commanded turn.
As humans we naturally rely on our inner ear and sense of balance to tell us what's "up" or "down", but in a moving aircraft you can move through a whole range of attitudes in "1G maneuvers" (where your body thinks down is where your seat is).
Little micro-movements we unconsciously make on the controls (or larger movements we may make consciously in response to turbulence or other perceved disturbances in the aircraft's attitude) based on what our ears and butts are telling us will eventually get us into trouble.
It's so easy that often instructors will have students create their own unusual attitudes in training by having the student close their eyes and simply try to fly straight and level - within a few minutes at most the student will invariably no longer be in level flight.
There's an exercise you can do on the ground to illustrate how imperfect your sense of balance and direction is, but it requires a large, flat, open area. We'll use an American Football field for this example:
Most people will not make it to their friend on the 50 yard line, because without a visual reference it's very hard to walk a straight line: You will veer off one way or the other, and some folks will even manage to walk in a complete circle (which is what eventually tends to happen over a large enough distance).
The same principles apply to flight, except there's a third dimension (vertical) to contend with.
Yes, definitely. This is from an NTSB accident report:
During the right turn, the pilot stated that he looked to his right to cross check the GPS and set up the autopilot for a coupled approach. He felt the airplane start to accelerate rapidly, and he looked back to the Primary Flight Display (PFD) which was “showing all brown with no sky and 6-7 chevrons, indicating a severe unusual attitude.” He tried to correct the unusual attitude, but said that he had severe vertigo, and was unable to regain control of the airplane. He elected to deploy the ballistic recovery parachute, and the aircraft impacted terrain in a nose low attitude in a creek bed.
The roll wasn't fully inverted, but it was extreme (120 degrees to the left):
The downloaded data showed that, just prior to the accident, the airplane went through a series pitch and roll oscillations, with maximum pitch values of approximately 26 degrees nose up, and 75 degrees nose down. The airplane reached maximum roll values of approximately 83 degrees right wing down, and 120 degrees left wing down.
So yes, it's absolutely possible for the aircraft to end up in an extreme attitude very quickly and easily: in this case the pilot just looked away to set the autopilot. The reasons why this can happen so easily have been discussed and commented in detail in this question.
Yes. Remember that once you get into a weird position, like upside down, you may be turning at the same time, creating a false gravity, so it does not feel like you are upside down. Usually you just feel "cockeyed", and if you try to adjust based on that "feeling", you will make the WRONG input which will make the situation worse. If you strap yourself inside a ball in an amusement park and get turned upside down, even then it can be difficult to tell exactly what is going on.
Many pilots have difficulty trusting their instruments and have to be trained to do so very strictly. When I was put "under the hood" for the first time, my instructor told me "you will go into a spin". I said "no I will not". He said, "Yes you will, everybody does the first time." As a matter of fact I kept the plane straight and level and did not go into a spin, but I was an exceptional case, 95% of students will start spinning the aircraft uncontrollably if they cannot see the horizon. JFK, Jr. was killed that way.
Let me just say, that first time under the hood I was sweating bullets and focusing my mind like I was trying to play speed chess against Bobby Fischer. Flying by instrument is INSANELY hard, if you have not trained on it for hours and hours. You have 5 different needles that you have to keep lined up at the same time. Even experienced pilots find manual instrument flying grueling and mentally taxing (thank god for autopilot).
Yes, very easily... Although 'sideways, nose down and at 200 knots into the ground before becoming a massive fireball' is more common
If it's only a short period they may just find themselves coming out of the other side of the cloud at a completely different attitude than they went in (and, likely, altitude too), but with anything more than just a quick cloud, it can be far more serious.
Pilots without an instrument license have something like a 3 minute life expectancy once they get into instrument conditions.
