Originally Posted by sarah737
Think le premier's question was: do you use speedbrakes to get to turb penetration speed?
My answer would be: NO! Stall margin is reduced with speedbrakes and the wing is stressed more.
Not quite Sarah
Is it adviseable to use them to prevent speed overrun or potentially hazardous in a possible upset situation.
I have checked the Flight Crew Training Manual for the 737 and it does not say that you shouldn't or can't. There is no section which explicitly relates to overspeed conditions in turbulent air, but, these quotes demonstrate that it can be used at or above VMO/MMO;
In relation to an unusual attitude recovery
Nose Low, Wings Level
In a situation where the airplane pitch attitude is unintentionally more than 10
degrees nose low and going lower, the airspeed is increasing rapidly. A pilot would likely reduce thrust and extend the speedbrakes. Thrust reduction causes an additional nose-down pitching moment. Speedbrake extension causes a nose-up pitching moment, an increase in drag, and a decrease in lift for the same angle of attack. At airspeeds well above VMO/MMO, the ability to command a nose-up pitch rate with elevator may be reduced because of the extreme aerodynamic loads on the elevator.
Again, it is necessary to maneuver the airplane's flight path back toward the
horizon. At moderate pitch attitudes, applying nose-up elevator, reducing thrust, and extending speedbrakes, if necessary, changes the pitch attitude to a desired range.
And in relation to stall speeds
Effect of Speedbrakes
For any airspeed, the angle of attack is higher with speedbrakes up. This increases initial buffet speed and stick shaker speed but has a lesser effect on actual stall speed.
So I can't see a reason why it should not be used if you overspeed due to turbulence, I was certainly demonstrated it's use together with idle thrust to reduce speed from above VMO/MMO.
That said, I stand to be corrected by someone more in the know and stress that this is my info based on the 737 Classic.
PP