You are semantically right concerning internal/external faults but what matter is that those erroneous informations won't be used by the flight systems but still be displayed to the crew for information and troubleshooting. All relevant systems based on erroneous outputs would be declared inop during the fault isolation sequence (AP/FD, A/THR, PROT, RTLU, WINDSHEAR, SPD LIM, TCAS)
Concerning FMGCs and FCPCs monitoring, the effect is a rejection of the faulty sources (channel); in our case, all 3 ADRs are declared faulty by them and rejected. There is no cockpit circuit breaker at probe-pitot level and what could be displayed is a fault on ADR pannel; one may want to turn it off.
ADR Single and ADR Dual faults are detected by ADR itself.
A Triple ADR Failure message (ADR 1+2+3 FAULT) only exist if the BUSS option is installed, this is a level 3 (Red & Master Warning).
This Triple ADR monitoring was NOT installed on the A/C.
A local ADR fault without ECAM message doesn't seem logical to ECAM protocol.
I really can't find a statement that FCPCs would reject more than 1 ADR source.
If 1 ADR is rejected the FCPC(PRIM) will use the average of the other 2.
NAV ADR DISAGREE is triggered if these 2 values deviates a certain value.
or if all 3 sources deviates from each other.
This message and following ECAM crew action demands the crew to monitor and switch of the ADR in error, to prevent it being used by FCPC.
~o~
FCOM:
MAIN REASONS FOR ERRONEOUS AIRSPEED-ALTITUDE DATA
The most probable reason for erroneous airspeed and altitude information
is obstructed pitot tubes or static sources.
Depending on the level of obstruction, the symptoms visible to the flight
crew will be different.
However, in all cases, the data provided by the obstructed probe will be
false.
Since it is highly unlikely that the aircraft probes be obstructed at the
same time, by the same amount, and in the same way, the first indication
of erroneous airspeed-altitude data available to flight crews, will most
probably be a discrepancy between the various sources.
CONSEQUENCES OF OBSTRUCTED PITOT TUBES OR STATIC PORTS
All aircraft systems using anemometric data have built-in fault
accommodation logics.
The fault accommodation logics are not the same for the various systems;
but all rely on voting principles whereby when one source diverges from
the average value, it is automatically rejected and the system
continues to operate normally with the remaining two sources.
This principle applies to flight controls and flight guidance systems.
Normal situation
Each PRIM receives the speed information from all ADIRUs.
It compares the 3 values.
Pressure altitude information is not used by the PRIM.
Each FE (Flight Envelope computer) receives the speed and pressure
information from all ADIRUs.
For each of these two parameters, it compares the 3 values.
If one ADR output is erroneous and the two remaining ADRs are correct
The PRIM and the FE eliminate it without any cockpit effect (no caution;
normal operation is continued), except that one display is wrong and CAT III dual
can no longer be available on the FMA.
If two ADR outputs are erroneous, but different, and the remaining ADR is correct,
or if all three are erroneous, but different
The autopilot and the autothrust are disconnected by the FE (whichever
autopilot is engaged).
If the disagree lasts for more than 10 seconds, the PRIM triggers the ADR
DISAGREE ECAM caution.
It reverts to Alternate 2 law (without high and low speed protection).
On both PFD, “SPD LIM” flag is shown, no VLS and no VSW is displayed.
This situation is latched, until a PRIM reset is performed on the ground
without any hydraulic pressure.
However, if the anomaly was only transient, the autopilot and the
autothrust can be re-engaged when the disagree has disappeared.
If one ADR is correct but the other two ADRs provide the same erroneous output or
if all three ADRs provide consistent and erroneous data
The systems will reject the “good” ADR and will continue to operate using
the two “bad” ADRs.
This situation can be met when, for example, two or all three pitot tubes
are obstructed at the same time, by the same amount, and in the same way.
(Flight through cloud of volcanic ash, takeoff with two pitots obstructed by
foreign matter (mud, insects)).
Human beings (the pilot) tend to use the same type of “fault accommodation”
principles to detect an erroneous IAS/altitude indication.
Flight crews will tend to reject the outlier information, if the other
two outputs are consistent.
This choice is, in the great majority of cases, correct; but, all flight crews
should be aware of very extreme and unlikely situations where two (or
even three) speed/altitude indications can be consistent and wrong.
- BEWARE OF INSTINCTIVELY REJECTING AN OUTLIER ADR
The following chart provides a non-exhaustive list of the consequences of various cases of partially or
totally obstructed pitot tubes and static ports on airspeed and altitude indications. It should be noted that
the cases described below cover extreme situations (e.g. totally obsctructed or unobstructed drain holes)
and that there could be multiple intermediate configurations with similar, but not identical, consequences.
Based on the information given in the preceding chart, it is clear that no single rule can be given to
conclusively identify all possible cases of erroneous airspeed/altitude indications. However, any case of
erroneous speed/altitude indications will always be associated to one (or more) of the following cues :
a) Fluctuations of airspeed indications;.
b) Abnormal correlation of the basic flight parameters (IAS, pitch, attitude, thrust, climb rate) :
– IAS increasing with large nose-up pitch attitude;
– IAS decreasing with large nose down pitch attitude;
– IAS decreasing with nose down pitch attitude and aircraft descending;
c) Abnormal AP/FD/ATHR behavior;
d) Undue stall warning or overspeed warnings;
e) Reduction of aerodynamic noise with increasing IAS;
f) Increase of aerodynamic noise with decreasing IAS.
RECOMMENDED PROCEDURES
The procedures described below are intended to provide flight crews with
general guidelines to be applied in case of suspected erroneous
airspeed/altitude indications.
FOLLOW ECAM ACTIONS
if failure undetected:
CROSSCHECK ALL IAS/ALTITUDE SOURCES:
ADR1,ADR2,ADR3 AND STANDBY INSTRUMENTS
If it is obvious that the outlier is wrong, select the corresponding ADR OFF
and reconfigure the PFD indications accordingly, by applying the ECAM drill
which will be automatically displayed.
Flight crews should, however, be aware that in very extreme
circumstances, it may happen that two, or even all three ADRs may
provide identical and erroneous data.
Therefore, the suspect ADR should only be switched OFF, if it is positively
confirmed that the two other ADR's are correct. If in doubt :
DISCONNECT AP,FD AND ATHR
FLY TARGET PITCH ATTITUDE AND THRUST SETTING
The initial pitch attitude and thrust values given in the QRH should be
considered as "Memory Items", since they allow "safe flight conditions" to
be rapidly established in all flight phases (takeoff, climb, cruise) and
aircraft configurations (Weight and slat/flaps).
Once the target pitch attitude and thrust values have been stabilized,
the expanded data of the QRH (Flight with Unreliable Speed Indication)
should be followed to determine the precise pitch attitude and power
setting required, as a function of the aircraft's weight, configuration and
desired speed.
After applying the QRH procedure, and when the aircraft is stable, the
flight crew should try to identify the faulty ADR (one or more).
Once the discrepant ADR has (or have) been positively identified, it
(they) should be switched OFF.
This will trigger the corresponding ECAM warnings and the associated
drills which should be followed to address all the consequences on the
various aircraft systems.