Question: I was studying for icing and a tailplane stall. I have looked up some internet pages and instrument flying handbook, and found the procedure below.

1. raise flaps to the previous setting. (To reduce down wash from the main wing so that reducing negative angle of attack of the tail and break the stall)
2. apply nose up elevator pressure (I don't get it. The nose up pressure will make the elevator to go up and wouldn't this increase the negative angle of attack and worsen the stall?)
3. do not increase airspeed unless it is necessary to avoid a wing stall. (Why shouldn't we increase airspeed?)

So now I'm trying to understand the reason why should a pilot do such actions. Can you help me out?

Answer: 
There was a NASA report on the [NASA/FAA Tailplane Icing Program Overview](http://ntrs.nasa.gov/search.jsp?R=19990019485&hterms=19990019485&qs=Ntk%3DDocument-ID%26Ntt%3D19990019485%26N%3D0), which covers the points raised by you. It lists certain actions that can be done to recover from a tail plane stall:

> 
> When the full tail stall was experienced during the power transition, the stall recovery procedure was:
> 
> 
> • Reduce thrust (may be airplane specific)
> 
> 
> • Pull back on yoke/ increase $\alpha$
> 
> 
> • Raise flaps
> 
> 
> 

* Raise flaps to previous setting

This is done mainly to undo the changes that caused the stall in the first place (reducing thrust is also done for this reason). The report says,

> 
> The major lesson learned to recover from a tail stall was to undo what was
> just done to cause the event.
> 
> 
> 

* Apply nose up elevator pressure

Basically you are pulling back on the yoke to increase the tail download so that the aircraft nose-down pitching moment is countered. From the report:

> 
> Pulling back on the yoke increased the camber of the tailplane, which provided enough tail download to counteract the nose-down pitching moment and increase the $\alpha\_{tail}$
> 
> 
> 

This sounds counterintutive as the conventional tail produces force in the direction opposite to the main wing. The report notes:

> 
> It was noted that this tail stall recovery procedure is opposite of the recovery from a wing stall. The reason for the difference is the location of the flow separation. In a wing stall, the flow separates from the upper surface of the wing, therefore reattachment is made by decreasing the wing $\alpha$. In a tail stall event, the flow separates from the lower surface of the tail and requires a positive increase in tail to reattach the flow.
> 
> 
> 

* Do not increase airspeed unless it is necessary to avoid a wing stall

The aircraft is already at a nose down attitude. Increasing speed will further excabarate the situation, which may put the corrective action beyond the capability of the tailplane.
For those recommended actions to be effective, two preconditions have been quietly assumed:

1. The tail surface produces downward lift and
2. The wing has positive camber.

Both can be assumed to be correct in almost any case. Now let’s look at the three recommendations in detail:

> 
> raise flaps to the previous setting.
> 
> 
> 

Flaps increase camber and shift the center of pressure backwards. In order to balance the aircraft with the same center of gravity location, the tail needs to produce [more downward force](https://aviation.stackexchange.com/questions/13855/why-cant-planes-use-only-flaps-in-the-tail-section-instead-of-stabilizers/13861#13861) with lowered flaps. Retracting flaps will unload the horizontal tail and reduce the stall condition.

> 
> apply nose up elevator pressure.
> 
> 
> 

This [adds tail camber](https://aviation.stackexchange.com/questions/44338/is-it-correct-to-say-the-up-elevator-position-decreases-the-camber-of-the-eleva) and helps to produce the same downward force at a less negative local angle of attack of the stabilizer. The induced angle of attack of the added tail camber will increase the local angle of attack at the stabilizer. This can only help momentarily, though, because it will make the aircraft pitch up and lose speed - unless you have a movable stabilizer which is used for trim. Re-trim with the new elevator setting and the change becomes permanent.

> 
> do not increase airspeed unless it is necessary to avoid a wing stall.
> 
> 
> 

When the main wing has positive camber, a lower wing angle of attack [shifts its center of pressure backwards](https://aviation.stackexchange.com/questions/47306/does-static-longitudinal-stability-require-download-on-the-tail/47308#47308). Therefore, the tail load and lift coefficient are lowest at low speed, and flying slowly will unload the tail. With rear center of gravity, tail load normally can even become slightly positive at low speed.

So in all cases the recommendations help to unload the tail and reduce the condition that let the iced tail stall.