Three times I have been aboard an aircraft which was out of control due to airframe ice, twice, descending with inadequate control. In each case control was regained by shedding the ice, twice by descending into warmer air, and melting it off, and the other time (a C 150 in which I was a 15 year old passenger) by climbing into colder clear air, and staying up so long that some came off by sublimation. One of those aircraft, a Cessna 303, was certified and fit for flight into icing conditions, and still could not manage it! An AD was issued on the type about it! The other, a Twin Otter, had oodles of power to get out, but was so heavily iced, that I was descending with full power. I learned to be more and more scared of airframe ice. Some non deiced airplanes can withstand some airframe ice, but the pilot has no means of controlling how much ice is accumulating, other than to get out of the icing conditions ASAP. Just avoid ice in non deiced aircraft, and approach with caution in deiced aircraft.