Anavex Life Sciences Corp (AVXL)

[nidan7500]

The pilot mistakenly believes they are flying with the wings level, but with a descent indicated on the altimeter and vertical speed indicator. This usually leads to the pilot "pulling up" or attempting to climb by pulling back on the control yoke. In a banking turn, however, the airplane is at an angle and will be scribing a large circle in the sky. Pulling back on the control yoke has the effect of tightening that circle and causing the airplane to lose altitude at an increasing rate, like water swirling in a drain or funnel. An increasing component of the lift being generated by the wings is directed sideways by the bank angle, not only pushing the airplane "upward" into the turn, but reducing the amount of lift which is holding the airplane up. At that point the aircraft is describing a descending circle or spiral, with a flight path that again resembles being in a funnel. In the ever-tightening, descending spiral the aircraft eventually exits the base of the clouds and/or hits the ground.[1]
To avoid this situation, a student pilot or a pilot under instruction uses a view limiting device to learn instrument flying proficiency under the supervision of a flight instructor. Instrument-rated pilots also use view-limiting devices supervised by an instructor or a safety pilot to practise instrument flight and maintain instrument flying proficiency.[3]

...AKA death Spiral analogy...