Svarin post #237
http://www.pprune.org/tech-log/45283...ml#post6477847
Three out of five components of the Flight Controls System have suffered anomalies :
- PRIM2 suffered a connectivity problem with ADR1, such problem is deemed HARD, which means permanent, not transient.
- PRIM1 stopped operating.
- SEC1 stopped operating.
These anomalies have consequences which can be verified using the Flight Controls Reconfiguration Schematics from FCOM chapter 27 :
- PRIM2 is tasked with THS motor because PRIM1 quit.
- PRIM2 is tasked with both elevator halves because both PRIM1 & SEC1 quit.
Additionally, PRIM2 operation is polluted because it lost connectivity with ADR1, thus reducing its discriminating capability while simultaneously getting fed multiple erroneous ADR data.
This simultaneous double failure condition : connectivity + erroneous data, is an extremely serious issue. I very much doubt that such apparently unrelated, simultaneous, totally different failures (external cause -> icing + internal cause -> wiring) were ever considered together during the design phase of the Flight Control System.
This extraordinary combination precisely affected the one computer which ended up being tasked with :
- interpreting sidestick commands on the pitch axis.
- sending orders to the hydraulic servo jacks located on the elevator moving parts.
- sending orders to the electric THS motor.
- providing whatever "protection" it deemed necessary to provide while in its undefined state (unreliable ADR data + lost connectivity with one ADR)
In the bold is exactly what in a normal situation PRIM 1 is capable to perform, so shouldn't be a problem for PRIM 2 too.
What I can add to your intresting observation is that in this situation, due to loss of the FCPC1(PRIM1) and FCSC1(SEC1), the Inboard (Green) servos are totally lost (both servos in dampening mode) and therefore are unable to assist the outer servos(BLUE/YELLOW) in large elevator deflections.
From the Technical Training Manual:
PITCH D/O (ELEVATOR) (3)
ELEVATORS NORMAL OPERATION
Each elevator servocontrol is connected to two computers (one FCPC
and one FCSC).
In the normal configuration, the inboard servocontrol is in active mode
while the outboard is in damping mode.
FCPC 1 having the servo-loop control priority:
- sets its dedicated servocontrol in active mode and ensures the servoloop control,
- commands the damping mode on the adjacent servocontrol (one solenoid valve (S) energized).
For the elevator servolooping computation the computers need to acquire:
- the elevator surface position,
- the elevator servocontrol piston position.
This information is sent by servocontrol transducers (XDCRs) units and
the surface position transducer (RVDT).
In the event of large deflection demands, the two servo-controls can
become active to avoid the saturation of one servocontrol.
ELEVATORS ABNORMAL OPERATIONS
HYDRAULIC OR ELECTRICAL FAILURE
If a servocontrol being in active mode is either not hydraulically powered
or not electrically controlled anymore,
the faulty servocontrol falls in damping mode and the adjacent one
becomes active according the servoloop reconfiguration.
If both servocontrols of one elevator are depressurized, both servocontrols are in damping mode which prevents fluttering.
When P1, P2, S1 and S2 are no longer able to control their dedicated
servocontrol (ie: inputs missing, electrical failure, etc...), the servocontrols fall in re-centering mode