ReplyWhen an airfoil (airplane wing) gets a deposit of ice, the ice tends to adhere to the skin of the wing and follow the upper surface of the wing (camber) due to the laminar airflow flowing over the wing surface. Naturally, the stall speed of the aircraft can be raised significantly when ice is present on a wing.
As long as the airplane's air speed is greater than the newly-raised [yet unknown] stall speed due to a coating of wing ice, the plane can continue flying, up to a point.
The heavy loading of ice on the complete airframe of a small general aviation airplane can cause a plane to lose altitude with the throttle at max. Think of it as slowly adding the equivalent weight of couple of passengers and/or luggage to the passenger compartment as ice builds on the skin of the plane. The engine is only so powerful and the wings can generate only so much lift. Besides, the wings are getting coated with ice and the ability of the wings to generate lift is slowly diminishing as the wing ice builds in thickness. The airplane can continue to fly, but it can be a losing battle with gravity.
Also, that plane (Cessna 172?) you were flying in could have had propeller icing. Prop icing can cause the air foil (spinning propeller) to have decreased thrust (lift). Lesser thrust from the prop would be the same as decreasing the throttle. Less thrust and the plane would slowly sink. Maybe the carb intake was slightly iced and a decrease in engine power would have resulted. I'm just taking a stab in the dark for I don't know what happened in your situation.
An aircraft that is experiencing a buildup of ice that is greater than the deicing equipment can remove from the wings, propellers, etc. is in a dangerous state. The pilot, whether he/she likes it or not, has become a TEST pilot.
When a pilot introduces an aerodynamic input to an ice laden aircraft, this can "upset the apple cart" and cause an out-of-control situation to develop in a matter of a few short seconds. Any of the following pilot-induced inputs can cause an aircraft to go out-of-control in an aircraft experiencing heavy icing:
- slowing down the aircraft to below the newly-raised [yet unknown] stall speed
- extending the landing flaps at the trailing edge of the wings to increase lift a slower air speeds
- lowering the landing gear
- extending leading edge wing slats for greater generated lift
- abrupt control inputs such as sharply banking the wings or pitching the nose causing a high speed stall
- disengaging the autopilot while airfoil control surfaces are greatly deflected (unknown to the pilot at the time the huge amount of deflection present) due to autopilot demands when a build-up of wing ice causes extreme control surface movement to keep the aircraft flying straight and level in the intended direction
Imagine that you are flying heavily iced in a traffic pattern to land at an airport (and, naturally, you are flying low and slow). If you run into trouble and gravity starts taking over due to decreased airfoil lift, you don't have enough altitude or airspeed to recover from the stall. Remember, the stall speed is higher and the pesky old ground comes up to meet you before a greater airspeed can be attained to get the wings flying again. [A stall can happen in the traffic pattern whether an aircraft is experiencing icing or not. I am talking about icing conditions.]
There was a twin turbo-prop passenger plane that crashed near Roselawn, Indiana in 1994 due to severe icing. The plane was being held by air traffic control at 10,000 feet altitude when the autopilot was disengaged by an uncommanded roll excursion as it was descending to 8,000 feet. The plane immediately experienced severe and abrupt out-of-control movements followed by a rapid descent to earth.
1994 Roselawn crash
http://en.wikipedia.org/wiki/American_Eagle_Flight_4184
Tiger93rsl, I hope this helps. This is not meant to be a treatise on the fundamentals of aircraft icing. Just some ideas and info to help answer your questions.
Originally Posted by twilli3967
I didn't say that out loud did I?