Flap position indication split of 15 degrees 737NG

[WhiteKnight]

Got the following quote out of a tech book:

"If the TE flaps are in a skew condition, the FSEU sends electrical power to the TE flaps bypass valve. This stops the hydraulic operation of the TE flaps. THE FSEU sends an input to the Flap Position Indication control to set the pointer 15 degrees apart.

If the skew sensor position is more than the position transmitter position, the FSEU makes the pointer for the skewed flap move 15 degrees in the extend direction. If the skew sensor position is less than the position transmitter position, the FSEU makes the pointer for the skewed flap move 15 degrees in the retract direction."

I don't understand the second part of the statement. Can anybody explain me when are the pointers move 15 degrees in the retract or extend position?


Thanks

WK

[IFixPlanes]

I quote my training Manual:

Functional Description(FLAP SKEW DETECTION SYSTEM)
There are eight flap skew sensors that interface with the FSEU. The number in the name of each sensor relates to the flap drive mechanism that the sensor connects to.
The excitation power for the sensors on the left wing is independent from the excitation power for the sensors on the right wing. Also, the wiring for the excitation power goes through each sensor.
The FSEU uses the data from the flap skew sensors to monitor the alignment of the TE flaps. The FSEU compares the data from symmetrical sensors. If the difference in the position of two symmetrical sensors is more than a limit, then there is a skew condition.
If the TE flaps are in a skew condition, the FSEU sends electrical power to the bypass valve. This stops the hydraulic operation of the TE flaps.
Also, during the skew condition, the FSEU sends an input to the flap position indication control. This causes the needles in the flap position indicator to be 15 degrees apart. The FSEU compares the skew sensor data to the flap position transmitter data to determine how to split the needles. If the skew sensor position is more than the position transmitter position, then the FSEU makes the needle for the skewed flap move 15 degrees in the extend direction. If the skew sensor position is less than the position transmitter position, then the FSEU makes the needle for the skewed flap move 15 degrees in the retract direction.

[WhiteKnight]

Thanks for your reply, but I still don`t understand. What is the "position transmitter position", just don`t have a clue.

And there is another question which just came up. If we have a flap asymmetry in a NG, the FSEU immediately stops the flap movement and the flap position indicator shows us the current conditon. Right?! But since this happens in a split second how can you actually see a flap asymmetry on the flap position indicator? I´m aware that on the classic I´ll get a 22° split and then it stops, thus I can easily see the problem!

Hope I made myself clear,

thanks,

[IFixPlanes]

My fault. :(
737CL has only a asymmetry funktion and the 737NG in addition has a flap skew funtion.
737CL :
The flap position indication comes direct from the two flap position transmitters.
Inside of the flap position Indicator is a comparator switch.
He compares the position of both pointers. When the two pointers separate by a predetermined amount the comparator switch closes and applies power to the asymmetry shutoff relay. The energized relay drives the trailing edge flap bypass valve to bypass and stops the hydraulic motor.
So the pointers show the real position.
737NG:
The flap position indication comes from the FSEU which gets his information from the two flap position transmitters.
The FSEU compares the data from the left and right TE flap position transmitters to monitor the position of the TE flaps.
If they are different by more than 9 resolver degrees, there is an asymmetry condition and the FSEU operates the bypass valve.
During an asymmetry condition, the needles on the flap position indicator show the actual data from the flap position transmitters.
But in addition you have 8 flap skew sensors (one at each transmission).
The FSEU use the values from the flap skew sensors to prevent skew.
The FSEU compares skew sensor 1 with 8, 2 with 7, 3 with 6 and 4 with 5.
If a predetermined value is exceeded the FSEU operates the bypass valve.
The FSEU compares the skew sensor on the skewed wing to the flap position transmitter. If the skew sensor position is more than the position transmitter position, the FSEU makes the needle for the skewed flap move 15 degrees in the extend direction. If the skew sensor position is less than the position transmitter position, the FSEU makes the needle for the skewed flap move 15 degrees in the retract direction.
It is important to anderstand that the indication on a 737CL is direct and on a 737NG the indication is generated by the FSEU.

[WhiteKnight]

great explanation, thanks a lot, that was extremly helpful