Originally Posted by A33Zab
Because the RTLU is not a Rudder DEFLECTION
Limiter but a rudder INPUT limiter.
I feel a bit uneasy by this statement, I must say.
The RTLU set the
position of the rudder limiter (physical limitation). In this case it was
between 5 and 6 degrees according to the graph on page 112 of the third Interim
Report, but 8 degrees after physical observation as stated in the second Interim
Report ... why such difference btw ?
IMO the TLU trace shows its RVDT angle ISO max. rudder deflection.
Ref. mm43:
RTLU GRAPH
Ref. PJ2:
R/PTLU
When the RTLU is at minimal (0° RVDT angle) the RTLU limits the rudder input to 4°, to be accurate this is 3.7° (CMM).
Interpolating the low resolution TLU trace its value was ~4.2° (RVDT angle) just before @02:10:05.
4.2° + 3.7° ~ 7.9° at which it was freezed by PRIM at the start of the speed monitoring process.
The RTLU ECAM MSG then indicates the unavailability for further rudder
deflection limitation calculation function, but the position of the rudder
limiter was already frozen.
The following is purely speculative since I am not able to prove with documentation.
The PRIM freezed the RTLU at the start of the monitoring process, but it can not control it because the TLU electrical motors are driven by the SECs.
The PTLU and RTLU share the control relays but have separate driver circuits inside the SECs. (so far true)
If the SECs continue to drive the PTLU to 5.8° RVDT angle the limiting position of the PTLU will be 5.8°(RVDT angle) + 3.7° ~ 9.5°.
at that position it detected the RTLU is not following its command position and triggers the TLU NOT AVAIL signal and F/CTL RUD TRV LIM FAULLT @ 02:10:18.
Nevertheless, at 02:13:00 the rudder reached 10 degrees ... not 'a little overshoot
The surface xdcr is placed at the lower side of the rudder, the lower servo is attached to the linkage before the RTLU, the upper and center input linkage after TLU.
Taking free play in all swivels & hinges in account the rudder deflection can be a bit more than the RTLUs position. (Due to poor resolution I would say just before 10°......9.5°?)
Could it be the consequence of the limitation value being unfrozen following a slats extension command ... ?
It is clearly mentioned in the second Interim
Report that the flaps were retracted but I have not seen a word on the slats
No, Slat/Flap input is combined (1 S/F lever).
If this was TRUE, the R/PTLU would have been driven to allow max. rudder deflection (35°) within 30 sec.
After 30 sec. this backup circuit will be isolated.
