A320 RTLU damage

[CMpilot1]

"To avoid damage on the RTLU (Rudder Travel Limit Unit) mechanical stop, the SLATS/FLAPS
should be retracted before all ADIRS are set to OFF simultaneously." These are excerpts from A320 SOP-AFTER LANDING chapter. I don't understand the connection. Could anyone shed some light on this. Thanks in advance!

[LEVEL600]

Slat position (slat extended) commands a movement of RTLU to low speed position (till mechanical stops) if no valid ADIRU/FAC as emergency (back up) recovery for landing. Mechanical stops can be damaged by this repetetive load with conseqetive RTLU fault/replacement. You can find more in WISE TFU 27.23.00.007 .

[vilas]

LEVEL600


I am unable to understand exactly how does the damage occur.
1. Does the damage occur when rudders are not neutral or in any position?
2. Shouldn't the damage occur if RTLU is in high speed position(More restrictive)? When flaps are left at one the RTLU is in low speed position.
3. If ADRUs are switched off RTLU will move to low speed(less restrictive) then why the damage?
4. Is there a parking position(Gust lock) for RTLU that causes the damage??

[LEVEL600]

Not a RTLU expert, but I can try explain scenario for this problem based on available information. Rudder position does not play role and gust lock function is not available in system. Damaged mechanical stops are internal stops of actuating screws (rotating shafts) inside mechanical part of RTLU, not rudder travel (variable) stops. Damage on this stops is generated by repetetive activation of "emergency return to low speed" mode, which drive a rotating shaft inside TLU until reaching mechanical stops. During normal RTLU operation shaft stops rotating before reaching mechanical stops, because system uses closed loop feedback from position transducer. This normal function does not put any load to mechanical stops. Emergency return to low speed condition will be activated on ground if CB for FAC are closed (it means RTLU is electrically supplied) and both FAC P/B are OFF and slat extended or ADIRU OFF (ADR data invalid for FAC) and slats extended. Yes, on ground is RTLU in low speed position, but can be moved further to hit mechanical stops. This is my explanation, at least in basis...

[vilas]

LEVEL600
Thanks. I think it makes some sense.

[CMpilot1]

Thanks guys for the reply. Not that I fully understood...however, it has given me a lead to look for.

[Chris Scott]

Quote:
"To avoid damage on the RTLU (Rudder Travel Limit Unit) mechanical stop, the SLATS/FLAPS
should be retracted before all ADIRS are set to OFF simultaneously." These are excerpts from A320 SOP-AFTER LANDING chapter.

Hi CMpilot1,
Is that from a current Airbus FCOM? What part of the after-landing SOP does that come from, and in what context?

It may be worth reminding some readers that operating a rudder PFCU rapidly to full-travel during ground ops can cause damage on any a/c.

[FlightDetent]

After Landing procedures / Vacating the runway.

See here, on a closely related thread: http://www.pprune.org/tech-log/561964-flaps-during-transit-a320.html#post8989364