737 alternate flap extension
Thread Starter
Joined: Jun 2006
Posts: 15
Likes: 0
From: Berlin
737 alternate flap extension
Hello,
I couldn`t find the answer to this question in our OM, in Bill Bulfer`s bibel nor in the FAQ section of PPRUNE.
Here it goes:
B hydraulic system operational but we perform an alternate flap extension (for example due to a trailing edge flap disagree). Afterwards we retract the flaps withe the alternate system. That means: Trailing edge flaps up, leading edge devices fully extended. Right? But now we place the alternate flaps master switch back to normal... I guess the leading edge devices retract now. Or am I wrong???
But Boeing states in its Trailing edge flap disagree NNC : "...the drag penalty with the leading edge devices extended may make it impossible to reach an alternate field"
Best regards
I couldn`t find the answer to this question in our OM, in Bill Bulfer`s bibel nor in the FAQ section of PPRUNE.
Here it goes:
B hydraulic system operational but we perform an alternate flap extension (for example due to a trailing edge flap disagree). Afterwards we retract the flaps withe the alternate system. That means: Trailing edge flaps up, leading edge devices fully extended. Right? But now we place the alternate flaps master switch back to normal... I guess the leading edge devices retract now. Or am I wrong???
But Boeing states in its Trailing edge flap disagree NNC : "...the drag penalty with the leading edge devices extended may make it impossible to reach an alternate field"
Best regards
Joined: Jan 2001
Aviation Qualifications: ATPL
Posts: 1,709
Likes: 35
From: UK
The LE devices would retract but only if system B pressure was available and that's highly unlikely as it's probably the lack of B pressure that gave you the TE disagree in the first place.
Thread Starter
Joined: Jun 2006
Posts: 15
Likes: 0
From: Berlin
...in case of loss of B hydraulic pressure I think I would call for the "loss of system B NNC" instead of the "trailing edge flap disagree NNC"... Wouldn`t you?
A trailing edge flap disagree can be caused for example, when the FSEU detects an uncommanded motion and it then closes the trailing edge flap bypass valve, so the trailing edge flaps must be conntrolled by the alternate system.
But you are also the opinion that the LEDs can be retracted by the abpve mentioned method. ...why does Boing not regard this fact in its NNC? I mean is there an obvious reason that I overlooked???
A trailing edge flap disagree can be caused for example, when the FSEU detects an uncommanded motion and it then closes the trailing edge flap bypass valve, so the trailing edge flaps must be conntrolled by the alternate system.
But you are also the opinion that the LEDs can be retracted by the abpve mentioned method. ...why does Boing not regard this fact in its NNC? I mean is there an obvious reason that I overlooked???
Joined: Jan 2001
Aviation Qualifications: ATPL
Posts: 1,709
Likes: 35
From: UK
I wasn't talking about complete loss of B pressure, just pressure to the flap system (for whatever reason). I had forgotten about the uncommanded motion and the FSEU. I don't know why the NNC doesn't mention it. I'll leave that for someone far more knowledgable than me!
Edited to say: From reading the FCOM, it says that only TE flaps are controlled by the alternate system following uncommnaded motion so the LE devices should still be controlled (retracted) by the lever and system B when the alternate master switch is in the off position.
Edited to say: From reading the FCOM, it says that only TE flaps are controlled by the alternate system following uncommnaded motion so the LE devices should still be controlled (retracted) by the lever and system B when the alternate master switch is in the off position.
Last edited by EGPFlyer; 1st August 2006 at 12:01.
