Dash 8 question

[cl65capt]

I'm sure you guys get this all the time but I'm curious about something. Why is it right before you take the runway the spoilers come up? It appears as though they stay up until the power is shoved forward. Just curious, everytime I see it the FO and I debate as to the purpose, just once I'd like to know. Thanks!

 

[xdashdriver]

On the 200, we do the FC check is done as you're taxiing onto the runway. Before that the controls are locked. So you might be seeing the FO do his FC check. Unless there's some kind of crosswind, they shouldn't stay up very long though. They're roll spoilers only on the 8-200. Not sure about the others.

Ray

 

[Whitestoneclimb]

I guess the easiest answer is to say: because the checklist says so. Now, if you want a little more info, read on.

The roll spoilers function as ground spoilers when three conditions are met:

1) All three gear on ground - weight on wheels function.
2) Power levers at flight idle or beta.
3) The Flight/Taxi switch is in the "flight" position.

The "taxi" position of the Flight/Taxi switch allows the spoilers to be retracted when on the ground. For some reason, deHavilland wants the Flight/Taxi switch placed in the "Flight" position when taking the runway. We then ensure they retract (by looking at the "powered flight control surface" indicator, not out the window!) when the power is advanced for takeoff. I'm not sure of the history of this, because we didn't always do this. We used to just push the power levers up and the Flight/Taxi switch would just "snap up" to the flight position (the spoilers would remain retracted since the power levers are above flight idle). Hope I answered your question

 

[Whitestoneclimb]

By the way, this was for the -100 series.

 

[Trash8Mofo]

I guess the easiest answer is to say: because the checklist says so. Now, if you want a little more info, read on.

The roll spoilers function as ground spoilers when three conditions are met:

1) All three gear on ground - weight on wheels function.
2) Power levers at flight idle or beta.
3) The Flight/Taxi switch is in the "flight" position.

The "taxi" position of the Flight/Taxi switch allows the spoilers to be retracted when on the ground. For some reason, deHavilland wants the Flight/Taxi switch placed in the "Flight" position when taking the runway. We then ensure they retract (by looking at the "powered flight control surface" indicator, not out the window!) when the power is advanced for takeoff. I'm not sure of the history of this, because we didn't always do this. We used to just push the power levers up and the Flight/Taxi switch would just "snap up" to the flight position (the spoilers would remain retracted since the power levers are above flight idle). Hope I answered your question

I think that if you don't manually take the flight/taxi switch to the flight position, the spoilers will never extend (ground spoiler mode) BEFORE you take-off. Without extending on the ground, you have no way to know that both of your lift/dump valves are going to OPEN together. If you get a Ground Spoiler Caution light IN FLIGHT, that means one of your lift/dump valve is opened in flight, and the other one is working properly (to be opened upon touch down), and you would still get the ground spoilers. However, you would not get a caution light if one of them is maulfunctioning shut until you touch down. Thats why you maunually switch it to flight before take-off to check.

Note: In order for the spoilers to extend on the ground, HYD pressure has to go through TWO sequential valves (lift/dump valves). If one of them does not agree with the other, you got yourself a Gound Spoiler Caution light.

 

[LearLove]

Basically its to verify the position of our roll spoilers. To do this we set the conditions for the spoilers to be deployed. That is:
1. WOW- all 3 gear (6 wheels) on ground
2. Power levers "flight idle" and
3. Flight/Taxi switch to "flight"

You can then look at the PFCS (powered flight control surface) Indicator located on lower part of the capts inst. panel and see the spoilers in the up position. As the power levers are advanced the #2 condition above is not met and the associated surfaces retract and you will see this on the panel and is one of the things the NPF checks at the start of the takeoff roll.

When we land and the power levers are at flight idle or below the conditions are then met again and the spoilers deploy. when exiting the runway the Flight/Taxi switch is put into the "taxi" position and the spoilers retract.

You see the roll spoilers on ALG aircraft painted red. This was done this winter to better check for or see contamination on them in icing conditions before takeoff.

Hope it helps

...if I only had a dime for every time somebody has told us our spoilers are up when in position .

 

[cl65capt]

Thanks for the answer guys. Learlove, I'm sure you get that a lot. I've been tempted to ask but have always kept quiet. I always figured it was normal. Thanks again guys!

 

[Freight Dog]

If I remember correctly, once you move your power levers past a certain point (forgot the actual number of degrees), but close to takeoff power, your flight/taxi switch will automatically spring to flight even if you don't manually do it before takeoff.

 

[Booker]

If I remember correctly, once you move your power levers past a certain point (forgot the actual number of degrees), but close to takeoff power, your flight/taxi switch will automatically spring to flight even if you don't manually do it before takeoff.

That's correct, except the PLA is a little closer to flight idle than takeoff power. You can still force the switch to flip with the control lock engaged.

 

[Hugh Jorgan]

"Mighty-mighty can 'o corn"

 

[91100 100 set]

There are some guys at ALG who do allow the flight/taxi switch to pop up automatically when the power levers are advanced for take-off. This is contrary to a factory issued bulletin stating that the switch must be manually moved to flight prior to advancing the levers. This bulletin was buried inside the big systems manual that we were issued in training, and I would venture to guess that most of the gray-hairs that do that probably never bothered to read the manual as thoroughly as a new-hire might. And most of the guys (one is particular) would not be receptive to "input" regarding the error of their ways in this area. If you know what I mean...

 

[Singlecoil]

Let's take a step back. If you were designing an airplane, would you design it to have all the lift-spoiling devices pop up right before takeoff? I didn't think so. The dehaviland engingeers didn't think that was a good idea either, that is why they made the switch pop up as the power levers are advanced. Ergo, in a normal taxi-out and take-off scenario, the plane taxis out, and takes off without the spoilers being depoyed.
Why we have somehow destroyed that great design feature and are now insisting that pilots deploy the spoilers immediately before takeoff is beyond me.