A320 Main Components (FLAPS)

[B737NG_Pilot]

Pressure-off brakes (POBs) lock the transmission when the slat or flap surfaces have reached the selected position or if hydraulic power fails.
Wingtip brakes (WTBs), activated in case of assymetry, mechanism overspeed, symmetricalrunaway, or uncommanded movement of the surfaces.

Can some one explain the difference between the two? If the Pressure-off brakes (POBs) lock the transmission how can there be uncommanded movement of the surfaces?

Also A flap disconnect detection system, which detects attachment failure and inhibits flap operation in order to prevent further damage.What would cause this ? A Bird Strike

[tubby linton]

Wing Tip Brakes Electro-hydraulic pressure-on disk- brakes, identified as Wing Tip Brakes,are installed near the end of the transmission system on both the slats and the flaps in each wing. The slats and the flap WTB's operate independently of each other. The central housing contains the friction disc pack which has stator and rotor discs. The central housing holds the stator discs, external splines on the torque shaft drive the rotor discs. The internal splines at each end of the torque shaft engage with the flap trans-mission system. At each end of the central housing is a hydraulic manifold which contains an annular piston. The torque shaft passes through the center of the two pistons. A solenoid valve and an electrical connector are installed on each manifold. The solenoid valves control the supply of fluid pressure to the pistons. The hydraulic supply to each WTB is as follows: - the Blue and Yellow systems supply the left flap WTB - the Blue and Green systems supply the right flap WTB. - the Blue and Green systems supply the left and right slat WTB. The two battery buses ( 701PP for system 1 and 702PP for system 2 ) supply power to the WTB solenoids through the SFCCs. This makes sure that power is available to the WTB if there is an engine power failure. Each busbar supplies one solenoid on each WTB. When the solenoids are energized, the fluid pressure moves the piston to release the spring force and puts the brake on. When the solenoids are de-energized, the fluid pressure returns through the solenoid valves and lets the brake off. Leakage of fluid past the piston seals returns through a drilled hole. If hydraulic pressure is not available to one piston, the remaining piston gives sufficient force to act against the spring to let the brake off.

[tubby linton]

Operation of the WTB The WTB's lock the transmission system if a failure occurs. If one or the other computer finds a failure: - the computer arms its own WTB circuits ( flap or slat channel ) - the other computer receives a WTB-arm discrete signal. If the second computer also finds the failure: - the computer arms its own WTB circuits - the first computer receives a WTB-arm discrete signal. When both SFCC's receive a WTB-arm signal they energize the related WTB solenoid valves. The WTB's lock the transmission system. If one SFCC does not operate, the other SFCC receives a WTB-arm signal automatically. If the other SFCC finds a failure, one solenoid valve on each WTB gets electri-cal power The WTB can only be reset on the ground through the CFDS.

The WTB will be applied in case of: - asymmetry - runaway - uncommanded movement - overspeed. When both SFCC's find any one of these failures: - the valve block solenoids on the PCU are de-energized - the POB's in the PCU are applied and stop their related hydraulic motors - each computer arms its own WTB circuits and sends a WTB-arm signal to the other computer - the WTB's lock the transmission system - the SFCC's give a class 1 level 2 caution and the ECAM display unit shows a failure message.

[Uplinker]

The brakes will be applied following mechanical failure of the mechanism(s), however caused.

[tubby linton]

Pressure off Brake A POB is attached to each hydraulic motor. It holds the output shaft of the hy-draulic motor when: - the hydraulic motors do not operate - the related hydraulic system does not supply sufficient,hydraulic power - the WTB stops the flap transmission system because of some system failures. The POB has a multiple friction-disk pack. Splines connect the stators to the POB casing and the rotors to the shaft in the center of the POB. Springs hold the friction disks together. When hydraulic pressure is applied to the POB, the friction disks are disengaged (against the pressure of the springs).To remove the POB, you must remove the related hydraulic motor first.

[tubby linton]

A flap connection strut connects the adjacent inboard and outboard flap ends. Attached to the flap connection strut are flap disconnect sensors. The sensors send signals to stop the flap movement, if the strut movement is more than the specified limits.
As to why whatever you can think of which would cause structural damage.

[Becky330]

Apologies if this is slightly off topic, but since we are on the subject of WTBs - I fondly recall being told during my initial LFUS by a senior training captain not to meddle with the date setting function of the onboard clock, as an accidental setting to a date too far ahead in the future would trigger the WTBs on, when it misleads the system into thinking that maintenance action is due.

I never found a reference in the pilots manuals. Is there any truth to this at all?

[B737NG_Pilot]

Thanks a ton tubby....

[FlightDetent]

Originally Posted by Becky330

accidental setting to a date too far ahead in the future would trigger the WTBs...
...Is there any truth to this at all?

Yes, such was the feature. To prevent flying the plane past the deadline of a functional check, there was a timer to engage the lock automatically. Once triggered you could not restore it back by just fixing the date and engineers were needed.

My original airline acquired aeroplanes mostly with GPS clock, hence we avoided learning first hand. The recollection above is based on shared knowledge and tips from the day zero batch of Airbus factory instructors. On the non-GPS clock equipped planes sometimes the CFDS would lose sync with the main clock and software confusion ensued across the FMGS circuits. Attempts to synchronize those back was the hazard area.

[Uplinker]

Originally Posted by Becky330

- I.... recall being told........not to meddle with the date setting function of the onboard clock, as an accidental setting to a date too far ahead in the future would trigger the WTBs on........ Is there any truth to this at all?

Yes. as FD says; Wing tip brake check by engineering is mandated every 10 days if I remember correctly. If someone changes the clock but changes the date as well by mistake, your aircraft could be stranded on the ramp, or even down route until engineers can be called to sort it out. You will not be popular !

[CaptainMongo]

This is from some research I did a few months ago on the Captains clock vice CFDIU clock on our early model A319/320’s: (there just isn’t a whole lot of info on clocks out there)

“Interesting side light - I did read at some point in the past the wing tip brakes required a check every 9 days which was based on the CFDIU clock. If the Captains clock was set incorrectly it could lock out the wing tip brakes because the CFDIU clock would also be wrong. I also read without a clock the CFDIU is unable to print a post flight report. At some time those two things were changed so as to not rely on the Captains clock.”

Also our MEL allows for the Captains clock to be inoperative but not the CFDIU clock. If someone has some different information please share.

Tubby linton thank you for the excellent WTB explanation.

[320busboy]

Uplinker

it’s automatically done by the SFCC’s.

WTB reset in mcdu sorts it. 5 mins.

[320busboy]

CaptainMongo

MEL is no go for cfdiu. There is no seperate part of the cfdiu such as a clock. It integral.

I remember the 7/10 days test and time lock. However spent time looking in fcom/fctl/airbus world and cannot find a single mention of it. You appear to be correct it has been changed. The question is how. I assume it’s an sfcc mod. Will dig a little deeper.