View Full Version : B737 Flaps Asymmetry
I've heard in case of asymmetry the drive will stop at such a maximum difference between flaps so the needles will be opened by the width of the small white segment on the indicator.
In other words the width of the white segment has an exact meaning.
Can anybody confirm this? :hmm:
B73567AMT
29th Aug 2003, 04:11
In the case of the B737-Classic, the assymetry detection performed isnide the flap position indicator. When the difference between the needles hits a certain degree, a switch inside the indicator is made which shuts a valve preventing further flap extension.
On the B737-Next Gens, the FSEU handles all of this.
cirrus01
29th Aug 2003, 05:22
737- 3/4/5 A comparator switch inside the indicator. When activated it provides power to the asymmetric shutoff relay which puts flap bypass valve to bypass.....which will stop flap operation .
alternate drive would still operate.
Flap asymmetric test switch in E & E bay :ok:
avioniker
29th Aug 2003, 08:23
On the NG aircraft:
Asymmetry Detection: 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. If the TE flaps are in an asymmetry condition, the FSEU sends electrical power to the bypass valve. This stops the hydraulic operation of the TE flaps. During an asymmetry condition, the needles on the flap position indicator show the actual data from the flap position transmitters.
The difference is very small and can not be seen by looking at the flaps or the indicator. The lockout criteria is roughly 3/4th revolution difference on the torque tubes as compared between left and right wings and the transmitters have an 800:1 turn ratio.
If one flap segment doesn't extend symetrically with the corresponding flap segment on the opposite wing there are sensors at each end of each flap segment (8 total) which will cause the flap skew sensing section of the FSEU to shut down the system and it will cause the flap needles to indicate a 15deg difference between left and right flaps. Once again you won't be able to see a difference just looking at the flaps.
There is one other time when the indicator will indicate a 15 deg split. That is when the exitation voltage to the position transmitters is lost. The system will once again be locked out in this situation because an assymetry can not be detected.
Any other needle split is an indication malfunction and the flap system should shut down as in an assymetry fault.
The system is so sensitive because the flaps have been redesigned on the NG aircraft. They are considered high lift before drag generating devices whereas on the previous versions of the 737 they were considered to have a higher drag element than lift. For roll trim problems the flaps are the first thing looked at in 9 out of 10 instances.
This is a somewhat lengthy but still simplified explanation. I hope it's adequate...
Thank you all.
So in just a few words, the width of the white segment on the position indicator doesn't mean anything at all... :*
avioniker
30th Aug 2003, 04:13
Actually that's a tolerance indicator. If you select flaps 1 both needles must be within the white band. The transmitters could be slightly misaligned so the needles wouldn't be exactly placed over one another. A good Tech wouldn't let this happen but we can't all be good, now, can we?
B73567AMT
31st Aug 2003, 00:09
Sorry, I guess I misread this question.
What are you guys talking about, the width of the makrs just below each unit number on the indicator?
Exactly.
Next question: what is the maximum asymmetry before the drive stops (737 classic)?
I'm afraid there's no exact answer possible, in typical Boeing fashion, but I hope I'm wrong...
Sorry, ASKFAP, I'm a bit slow....
Now I got it, thanks! :ok: :D
Uaaaaauuuuuuuuuuuuuuuuu... it's like oh my god! Great!
Thanks for your explanations, ASKFAP:D