Question Brazil ATR 22 flat spin crash

[JohnN]

So what would cause the plane to enter a flat spin, other than pilot incompetence?

 

[AJ]

As far as I have understood: possibly ice on the wings caused loss of lift. No plane can fly without lift.

 

[VsubT]

Worth a watch: Blancolirio's take on this incident. He does a thorough and fair job of explaining possibilities with the information available for aviation incidents.

Lance

 

[JohnN]

Worth a watch: Blancolirio's take on this incident. He does a thorough and fair job of explaining possibilities with the information available for aviation incidents.

Lance

Good review of the crash, but no direct explanation for the flat spin. If the plane type was that unstable, wouldn't this problem have happened previously? I get icing can cause a drop in lift from the wings, but it doesn't seem that a falling brick would enter a flat spin without some pilot action

 

[rhwestfall]

if it was icing: https://www.aopa.org/-/media/Files/AOPA/Home/Pilot-Resources/ASI/Safety-Advisors/sa11.pdf

 

[rhwestfall]

His explanation of the vulnerability of that aircraft.....

 

[VsubT]

Good review of the crash, but no direct explanation for the flat spin. If the plane type was that unstable, wouldn't this problem have happened previously? I get icing can cause a drop in lift from the wings, but it doesn't seem that a falling brick would enter a flat spin without some pilot action

Good question. Impacts of icing aren't predictable in the sense that ice can build unevenly, shed suddenly, jam controls, reverse expected control responses, etc. Failure of part of a deicing system can have similar impacts. These impacts can be equal to or greater than the available contol authority at times.

The ATR-72 roll incident on p.11 of the ASR document @rhwestfall cited is a great example of this. Hope that's helpful,

Lance

 

[Searcaigh]

I believe it's a combination of events initiated by a stall caused by icing on the wings and the design of the ATR with the high tailplane making controls inoperable to put the nose down and accelerate out of the stall which happened around 17,000 feet.

We'll know more once the data from the black box has been analysed.

 

[MCKNGBRD]

The ATR-72 is known to be especially touchy in light to moderate icing conditions; the high aspect ratio wing gets really twitchy as ice forms on the lifting surface. As you lose lift from wing contamination (ice buildup), you need to increase the angle of attack to maintain altitude. Increasing the AoA puts the high T-tail into the aerodynamic 'shadow' of the wing itself; soon, the control authority of the tail is compromised and you lose pitch control, typically about the same time you reach the critical AoA, beyond which you have a stalled wing.

As you stall the wing, you need to add power and push the nose down, which is damn near impossible with the T-tail not working well in the 'wake' of the main wing. Horrible situation, but avoidable if the aircrew had paid attention to PIREPs in the area and descended to warmer temps.

Byrdman

 

[JohnN]

The ATR-72 is known to be especially touchy in light to moderate icing conditions; the high aspect ratio wing gets really twitchy as ice forms on the lifting surface. As you lose lift from wing contamination (ice buildup), you need to increase the angle of attack to maintain altitude. Increasing the AoA puts the high T-tail into the aerodynamic 'shadow' of the wing itself; soon, the control authority of the tail is compromised and you lose pitch control, typically about the same time you reach the critical AoA, beyond which you have a stalled wing.

As you stall the wing, you need to add power and push the nose down, which is damn near impossible with the T-tail not working well in the 'wake' of the main wing. Horrible situation, but avoidable if the aircrew had paid attention to PIREPs in the area and descended to warmer temps.

Byrdman

Thanks. So gross pilot error.