That’s called a flat spin. When props are feathered there are turned so that the blades go to zero pitch meaning no thrust is being produced. Propellers are adjustable to provide max rpm and thrust at take off but then we can adjust them in cruise where the air is thinner to take a bigger “bite” of the air. This provides a big fuel savings. With ice building up on the propeller and wings neither are capable of creating thrust or lift because the laminar flow over them has been disrupted by the rough ice. With no thrust pulling you forward, a wing not creating lift and an airplane quickly getting heavier with ice, the airplane might as well be a brick. There are ways to recover from a stall. In most aircraft we push forward on the controls to regain that airspeed, add opposite rudder to stop the roll and recovery is not difficult. In an airliner with many passengers and bags and possibly a few thousand pounds of ice on the tail and wings the CG(center of gravity) could have been slightly aft making pushing forward on the controls ineffective. We’ll need to hear the tapes, but unfortunately stall spins are what kill a majority of pilots and passengers in aviation and is by far the most common type of accident. As mentioned in my previous post, accidentally moving those propeller pitch controls to the feathered low drag position when already at a slow speed would only accelerate the process of the stall and it would happen so fast they couldn’t be corrected in time to keep the airplane aloft. One more thing about stalls… typically when they happen one wing loses lift and stalls first causing that wing to drop and the other to quickly rise causing you to roll one direction or the other. That’s what starts the rotation or “spin”. Not only that but if the wrong control inputs are made it can tighten the spin increasing the rotation speed or even cause you to roll inverted. In todays world nothing would surprise me as far as a nefarious attack, but with my background and knowledge of airplanes and aviation I’ve seen this exact same scenario play out too many times. Most of the time it’s smaller general aviation aircraft so they don’t get as much attention. If you search stall spin crash on YouTube the results would take you years to watch though.

As airline pilots we are trained to a level that far exceeds many professions level of expertise before we are allowed to get behind the controls of an airplane carrying that many people, but we’re still human and still screw up. If the weather is adding complexity to the situation or a system such as the anti-icing equipment fails, those distractions can cascade into mistakes. Its usually takes a combination of things to happen for an airplane to crash, and I believe we’ll see that here as well after the investigation is complete.