HarryStanhope From Australia, joined May 2012, 16 posts, RR: 0 Posted (7 months 1 week 2 days 2 hours ago) and read 1589 times:
I'm not sure if this happens for every model of the Dash 8 or if its just a particular one but the other day I was holding short of the runway - I noticed the Dash in front of me had the spoilers up, up until he was rolling for the take off. I'm not sure when he first put them up.
I've seen it a few times now but haven't been close enough to pay all that much attention.
Why would he have the spoilers up for so long? If they get tested for operations wouldn't it be only for a few seconds?
Is it a De Havilland procedure or airline procedure? (It was a QantasLINK flight)
doug_Or From United States of America, joined Mar 2000, 3167 posts, RR: 4 Reply 2, posted (7 months 1 week 2 days 2 hours ago) and read 1589 times:
Its been a while, but IIRC, there is an automatic spoiler deployment mode on some/most models of the dash 8. When the mode is armed, there is weight on the wheels, and the power levers are below flight idle, the spoilers are deployed.
You see them deploy as the aircraft enters the runway because the pilots are arming the auto deployment mode as part of the before takeoff checklist (and because the power levers are at a taxi setting with weight on the wheels).
When takeoff power is applied, the requirements for the spoilers are no longer met (power levers are now above flight idle), and the spoilers retract.
320tech From Turks and Caicos Islands, joined May 2004, 487 posts, RR: 5 Reply 3, posted (7 months 1 week 2 days 1 hour ago) and read 1589 times:
Quoting doug_Or (Reply 2): When the mode is armed, there is weight on the wheels, and the power levers are below flight idle, the spoilers are deployed.
This is correct. On the -100 series, at least, and I think on all others, there is a magnetically locked switch on the glare shield called the "Flight / Taxi" switch. On the ground, the pilot puts the switch into Taxi, locking the spoilers down. Prior to take off, the pilot sets the switch to Flight, and the spoilers extend. They retract automatically when the power levers are advanced. I believe that if the pilot fails to set the switch to Flight, it will go to Flight automatically on power lever advance, but I'm not 100% sure.
What the benefit is, other than possibly keeping snow out of the spoilers, I don't know.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
AA737-823 From United States of America, joined Mar 2000, 5386 posts, RR: 11 Reply 4, posted (7 months 1 week 2 days 1 hour ago) and read 1589 times:
Quoting 320tech (Reply 3):
What the benefit is, other than possibly keeping snow out of the spoilers, I don't know.
Improved wheel braking.
At my home airport, "flight" mode is apparently armed before taxi out, as you see the little Dashes leave their ramps with spoilers already up. Freaked me out the first time I saw it!
moose135 From United States of America, joined Oct 2004, 2020 posts, RR: 12 Reply 5, posted (7 months 1 week 1 day 16 hours ago) and read 1589 times:
Good to know. I've seen the US Express Dashs at CLT with the spoilers up when taking the active, and wondered about that. I just assumed that the airplane was so stunningly overpowered, that there would be no controlling it without the spoilers up.
bio15 From Colombia, joined Mar 2001, 1089 posts, RR: 7 Reply 6, posted (7 months 1 week 1 day 9 hours ago) and read 1589 times:
Quoting 320tech (Reply 3): This is correct. On the -100 series, at least, and I think on all others, there is a magnetically locked switch on the glare shield called the "Flight / Taxi" switch. On the ground, the pilot puts the switch into Taxi, locking the spoilers down. Prior to take off, the pilot sets the switch to Flight, and the spoilers extend.
This is true, but it's a feature only for the Dash 8-100 and the Q400 Series.
As per the Q400 AOM, the spoilers extend if:
- The FLIGHT/TAXI switch is in the FLIGHT position
- Both power levers are set to less than FLIGHT IDLE + 12º
- WOW (Weight on Wheels) indicates the airplane is on the ground.
For the -100 it's exactly the same, but I'm not sure about the 12º.
---
Basically, the switch is set to TAXI after landing to retract the spoilers, and remains in that position until the next takeoff. During the procedures before takeoff, the switch is taken to the FLIGHT position. At this time you will have the spoilers extend momentarily until you advance the power levers for takeoff.
The switch is held by a solenoid in the TAXI position, and it is de-energized if you advance the power levers past the threshold (12º for the Q400). Therefore, if you forget to move the switch to the FLIGHT position, it will snap to the FLIGHT position while applying power. It's a real Tell-On-The-Forgetful-F/O feature It caught me a couple of times on the -100.
DashTrash From United States of America, joined Aug 2006, 1321 posts, RR: 4 Reply 8, posted (7 months 1 week 1 day 6 hours ago) and read 1589 times:
Quoting bio15 (Reply 6): The switch is held by a solenoid in the TAXI position, and it is de-energized if you advance the power levers past the threshold (12º for the Q400). Therefore, if you forget to move the switch to the FLIGHT position, it will snap to the FLIGHT position while applying power. It's a real Tell-On-The-Forgetful-F/O feature It caught me a couple of times on the -100.
I know a guy who forgot to put that switch up, only to have the thing come apart when it snapped up on it's own at power application.
Quoting moose135 (Reply 5): I just assumed that the airplane was so stunningly overpowered, that there would be no controlling it without the spoilers up.
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It caught me a couple of times on the -100.
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