airbubba - "I wonder if the confusion is over nomenclature.
The speedbrake lever has three labeled positions, Down, Armed and Up. When the lever is fully up on the quadrant, it is in the Down position. When it it fully down, it is in the Up postion. I wonder if the NTSB brief meant the handle briefly moved down to the Up position, then returned to Armed."
-----------------------------------------------------------------------
Huh? Down is up, and up is down? 9,000+ hrs on the airplane and "up on the quadrant", along with your other explainations, confuses the heck out of me so I wonder how an ESL(english as a second language) person, or a non pilot, could understand your statements.
The handle fully forward is down(also 'stowed').
There's a slight detent that can be felt when the handle is first moved aft. That is the 'armed' detent and a light is activated that indicates the speedbrakes are 'armed'.
If the speedbrakes are 'armed' they should deploy with WOW(weight on wheels). Armed, or not armed, they should deploy when the thrust reversers are used.
Moving the handle aft(back/rearwards/deployed/out) deploys the speedbrakes in flight. With WOW it also deploys the inboard ground spoilers.
The autobrakes, if armed, should always work. If the braking action by the spoilers and reverse thrust is greater than the selected autobrake setting(1,2,3,4, max) the brakes don't engage until the total deacceleration rate is below the selected autobrake setting.
For example, thrust reverser and spoilers is about a deacceleration rate of just under 3. So if brakes 2 are selected the brakes won't be applied until thrust reverse effectiveness drops below '2' as the a/c slows.
If brakes 3 are selected the brakes are used slightly at high speed(w/thrust reverser and spoilers) and increase brake pressure as the a/c slows and thrust reverse effectivness decreases.
Brakes 4/MAX apply brakes harder throughout the landing.
From a pilot's perspective on a dry runway brakes 2 aren't felt until the thrust reversers are stowed. Brakes 3 are felt slightly during the landing roll. The application of brakes 4, or more, are obvious on a dry runway even when thrust reversers are being used.
Obviously runways less than dry have different reactions. The difference between what the pilots expect and what they actually experience is how 'reported braking action' reports are generated.
Last edited by misd-agin; 17th Jan 2011 at 14:48.
Reason: added text