Not so good news about flight 3407

[LJ45]

91 x 1.3 = 118.3 or 119 flip swith ref now 139

 

[ultrarunner]

91 x 1.3 = 118.3

Sounds right I suppose....big 'ole straight-wing airplane like that, reasonably light, could have a Ref of 119.

Contamination bumped that by 20 kts.

 

[belchfire]

91 x 1.3 = 118.3 or 119 flip swith ref now 139

However the stick shaker is probably run off some kind of AOA sensor which isn't adjusted for icing conditions...

 

[atrdriver]

However the stick shaker is probably run off some kind of AOA sensor which isn't adjusted for icing conditions...

The AOA sensor adjusts in the ATR, I would bet it does in the Q400 as well.

 

[ultrarunner]

I suppose a Q driver will chime in, but yeah, I'm thinking the switch for contamination simply reschedules IAS for the purposes of flying a faster speed.

The airplane will still stall at a particular AOA and the shaker and pusher will fire accordingly. You would not arbitrarily reschedule those types of safety devices.

 

[BirdCatcher]

However the stick shaker is probably run off some kind of AOA sensor which isn't adjusted for icing conditions...

The increase ref switch lowers the AOA required to activate the shaker/pusher.

 

[Kaman]

Agreed...Critical AoA is not a function of Airspeed. Aerodynamics 101...Logic would conclude that the engineers design the stall warning system to activate when the critical AoA is exceeded. On the SAAB that is the only function of the AoA vanes. Cannot speak to the "Q". But, I am thinking for the simplicity of certification that in a straight-wing turboprop the AoA vane is used only for stall warning.
I wish that the press would show more restraint and less sensationalism in this mishap.

 

[centralpilot]

I suppose a Q driver will chime in, but yeah, I'm thinking the switch for contamination simply reschedules IAS for the purposes of flying a faster speed.

The airplane will still stall at a particular AOA and the shaker and pusher will fire accordingly. You would not arbitrarily reschedule those types of safety devices.

Can't speak for the Q, but as atrdriver said one post before yours, the ATR did adjust the AOA margin when horn de-icing was selected on and was manually reset to normal when turning ice protection off. This wasn't arbitrary rescheduling, but rather intentionally increasing safety margins to account for the negative effects of ice accumulation.

 

[ACL65PILOT]

They are leaking this out slowly so that when it fully comes out it is not a bomb shell.

FWIW, it could be any of us, and if you think you are above it, you have not been aviation long enough.

 

[LJ45]

Agreed...Critical AoA is not a function of Airspeed. Aerodynamics 101...Logic would conclude that the engineers design the stall warning system to activate when the critical AoA is exceeded. On the SAAB that is the only function of the AoA vanes. Cannot speak to the "Q". But, I am thinking for the simplicity of certification that in a straight-wing turboprop the AoA vane is used only for stall warning.
I wish that the press would show more restraint and less sensationalism in this mishap.

a DHC 8 driver posted it does increase the stall warning speed (angle) and the Stall warning comes on BEFORE the critical AOA is reached...correct? That is why it is called a warning...to prevent a stall.