Tailplane Icing

MarineGrunt

Will kill for peace.
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When I heard the the initial circumstances of last nights tragety, I thought back to when I read this AC. While I'm not starting this thread to speculate on the causes of this accident, I think it is useful for us all to take a peek. Regardless of the causes, we should always be taking opportunites to learn or re-learn. It covers a lot of basic every day stuff, but there is also a little extra need to know stuff.

Advisory Circular 91-51A - Effect of Icing on Aircraft Control and Airplane Deice and Anti-Ice Systems

My thoughts and prayers are with the families, friends, loved ones and anyone else effected by this accident. If we can take anything out of this, it should be a reminder of how fragile we all are, and more importantly, the responsibility we undertake every day when we push back from the gate.
 

7KCAB

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Aircraft with fixed horizontal stabilizers (elevator trimmed) are much more succeptable to elevator blanketing than aircraft with stab trim. With stab trim, if you get ice build-up, you can alter the angle of attack of the stabilizer to get clean air to the elevator (to a point).

There was a NASA video that I saw one time showing a Twin Otter trailing behind a water tanker aircraft spraying water to build ice at altitude. There is a closeup camera angle of the horizontal stabilizer leading edge, and once it built up enough ice to blanket the elevator, there isn't anything to keep the plane from pitching over as the elevator becomes completely ineffective.

I experienced this, thankfully in a Seminole of all things with a full flying stabilator and no autopilot. We built up a good bit of clear ice in the decent and on the ILS. When I pulled the first notch of flaps, the yoke began shaking pretty violently, so I immediately undid the last thing I did (flaps) and landed with zero flaps. I have always wondered what would have happened in a plane with a fixed horizontal stab.

According the preliminary release of the CVR events, the aircraft pitched over almost immediately after flaps were selected.

A Citation Ultra crashed in Colorado a few years ago on approach in freezing rain and it appears tail icing was to blame. This accident prompted the recommendation to disconnect the autopilot when in these conditions so as to be able to feel what the plane is telling you. That aircraft departed controlled flight on a regular ILS without any word from the crew - very similar to what it sounds like might have happened in Buffalo.
 
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