Bypassdoors on Dash 8 100

[deuzx]

Anybody who knows what are controlling bypassdoors on the DeHavillan Dash 8 100? Some pilots said to me they are "livin`their own lifes". Usually I see them closed when I observe in cockpit and sometimes open, but i do not see them push any buttons. Anybody who knows?

[Pilot Paul]

Not flown the 100 - but as far as I know they are the same as the 300 (which I have flown). You have two buttons in the cockpit just to the left of the centre of the main instrument panel labelled "Engine Intake Bypass Door n" (n=1 or 2). To open the doors push them in! The idea is to stop unwanted solids (e.g. ice) accumulating at the back of the plenum chamber. Normal procedure is to open them in icing conditions, although some airlines leave them open all the time as there is little penalty in doing so and it's one less thing to forget!. They are electrically actuated, operated from the 28 VDC system. They are also heated (by 115 VAC) to prevent ice accretion although this only activates if the OAT is less than 15 degress C. Finally, if they are closed and something heavy hits them , there is a breakable diapragm and shear door built into the front face of the bypass door to ensure such objects are ejected anyway and don't enter the rotating engine!

Hope this helps

Pilot Paul

[deuzx]

Okay. As you see I am not a airliner pilot, but have the interest there. I am going to fly the Dash 8 and Boeing 737 in a full flightsimulator with a friend of mine in February. It is a extraordinary sp. deal between many enthusiasts on a "given" level (should know more than how many engines there are on a 737) and SAS Flight Academy on Oslo Gardermoen.

I often hear that pprune do not welcome flightsimmers on this forum? Is that true? If I understand correct it is okay to ask relevante questions and not that newbe q. as "What is difference bet. Cessna 152 and B777?"

I do not have good enogh colorsight to get medical for IR so I think I never will become an airline pilot. But that`s life.

Thanks alot for the answer!

And, by the way, do you know a place to find an official AOM for Dash 8 100/300?

[Panama Jack]

Same thing on the -100's and -200's as on the -300's.

Yes, it is true, some airlines leave them open all the time-- the performance penalty is something like 2%.

[AerocatS2A]

They are electrically actuated, operated from the 28 VDC system. They are also heated (by 115 VAC) to prevent ice accretion although this only activates if the OAT is less than 15 degress C.
Actually, it is the engine intake flange that is electrically heated, not the bypass doors. It is heated when the bypass doors are open, the engine is running and the OAT is below +15.
We operate the bypass doors in conjunction with the other ice protection equipment when ever we're in icing conditions, i.e., below +5 in flight and with visible moisture present.

[fortuna76]

In my company we have recently changed from bypass doors open in icing conditions to bypass doors open all the time. The reason for this was that apart from the obvious ¨you can´t forget it then¨, it is more cost affective to leave them open all the time. It appears that the cost of the loss of 2% power is less then the cost of installing new doors after XXX cycles. Long live the beancounters! :}

Having said that though we do close them at the end of the day to avoid FOD on an overnight stop.

Regards.

[deuzx]

So, the safe way is to have them open all time! :)

I also wonder about the aircondition system. Is it procedure to have bleeds minimum and OFF under takeoff under every conditions? I see Widerøe use it when I fly with them here in Norway. Maybe it is because of the short fields, when we fly on the coast of northern norway.

[AerocatS2A]

Bleed air should be Min Off for take off as per the flight manual. If, for some reason, you require the bleeds to be Min On then there is a performance penalty on take-off. For our company we require the bleeds to be on and must assume a temperature 7 degrees higher than what it actually is when working out our take-off performance. I think there is a flight manual supplemant that covers this.

[deuzx]

Okay. Do you know about anything in range for everyone, on the internet? I am not connected to an airliner that uses Dash8. I should had an AOM. Esp. now when I am going to fly this machine on a flight academy. (simulator).

[AerocatS2A]

I don't know of anything freely available on the internet.

[Plain Driver]

Panama Jack wrote:
-- the performance penalty is something like 2%.
:hmm: Actually, it more like 0.2%. Tried it during cruise (FL240, ISA-5) the other day and saw .3% drop in torque.
Also, there is an AFM limitation at ISA+25: with SAT above this temperature the doors need to be closed. Presumably this is to force more air through the oil cooler instead of letting it out the bypass door.
PD.