augustusjeremy;
The question is: Did they turn on ADIRU1 again ? Wouldn't it take some time to realign ? And how would it realign without trustful IR data (as the other two IRs were probably disagreeing ?)
[my bolding]
It should be clearly understood by anyone examining this course of action, that once the rotary switch is turned OFF, the IRS cannot be re-aligned without landing the aircraft. That fact has been understood since 1972 when INS first entered airline service.
The irreversibility of this action is noted in the OEB thus:
• If all ADIRU operative before failure:
If one IR is self detected faulty or if the ATT red flag is displayed on the Captain or First Officer PFD, the affected IR and the corresponding ADR must be disconnected.
NAV IR 1(2)(3) FAULT, or ATT flag displayed on CAPT (F/O) PFD
-IR (affected) pb …………………………..…… OFF
The affected IR is the one self-detected faulty or supplying the PFD displaying the ATT red Flag.
The OFF light may not illuminate
-ADR (corresponding) pb ………..…………… OFF
ADR 1 corresponds to IR 1.
ADR 2 corresponds to IR 2.
ADR 3 corresponds to IR 3.
The OFF light may not illuminate
-IR (affected) MODE rotary selector ……….. OFF
The IR mode rotary selector is set to OFF in order to de-energize the ADIRU. The OFF lights of the IR and ADR pushbutton will go off.
Setting the IR mode rotary selector to OFF is an irreversible action. Therefore, both PF and PNF must clearly identify the corresponding selector before setting it to OFF.
• If IR 1(2) affected:
In order to prevent possible failure of ADIRU 3, the flight crew must switch the AIR DATA and the ATT HDG in the following order:
-AIR DATA SWTG ………..………..……… CAPT (F/O) ON 3
-ATT HDG SWTG ..………….…………….. CAPT (F/O) ON 3
Once the rotary switch is turned OFF, all attitude information from that ADIRU is lost. Depending upon faults, one may lose all attitude information (as per the cautions expressed in the OEB) if one does not strictly follow this OEB.
Needless to say,
one is extremely careful and deliberate in taking these actions. One does not execute these actions swiftly or without confirmation with the other crew member. One very obvious reason for caution is, the ADIRUs are not numbered sequentially from left to right, (1,2,3) but are instead numbered 1,3,2 - to represent the (schematic) correspondence of the ADIRU to the left (captain) and right (First Officer) systems and the #3 backup for either system depending upon the data switching. Among other reasons, when on IRS-ONLY or GPS Navigation, (beyond land) one never messes with the ADIRUs unless absolutely necessary.
Some will think and perhaps argue that the situation faced by the QANTAS crew, if faced by the AF447 crew (which is the case in fact being argued here), that swiftness is the order of the day due to rapidly unfolding/deteriorating circumstances. I submit that that is not the correct approach as mistakes can and will be made any emergency procedure is rushed. These are "mission-critical" systems the loss of which is a threat to the safety of the flight. At the same time, one does not dawdle but gets on with it directly - a well-trained crew that is familiar with both the system and the procedure can execute this swiftly and accurately. A crew that is hesitant because they do not know the system thoroughly may be at a disadvantage depending upon other circumstances. The QANTAS crew could not have been expected to comprehend what was going on with their aircraft.
I frankly doubt if this scenario unfolded but it is, as other scenarios are, a possibility.
takata;
What in AF447 ACARS sequence is similar to QF72 case?
- answer: nothing.
So, maybe its time to drop this claim for lack of any substantial or relevant fact to come with.
Precisely.
augustusjeremy;
I think you have the feedback you were seeking...
For orientation and understanding, the respective panels are shown below:
ADIRU control panel - Overhead Panel, top left
Switching Panel - forward Pedestal
