[Peetwo]

#ET302 v VH-FNP - Like Chalk & Cheese?

I note that yesterday there was two significant Annex 13 AAI reports made public, one was the prelim report into the tragic accident of Flight ET302 by the Ethiopian AAIB - see HERE - and the other was the ATSB final report into a Virgin Australia Regional Airlines Airbus A320 charter flight occurrence departing Perth, on 12 September 2015 - see HERE.   

Even though it is 3 years 6 months and 24 days since the VARA VH-FNP, the ATSB considered the findings and safety issues significant enough to put out the following media blurb...

Unreliable airspeed indication and stall warning

Airbus is proactively updating software on its A320 aircraft to ensure pilots receive alerts at an appropriate level of priority during periods of multiple alerts and high workload.



The update follows an ATSB investigation into an unreliable airspeed indication and stall warning involving a Virgin Australia Regional Airlines Airbus A320 near Perth Airport on 12 September 2015.

While passing through 8,500 ft, the aircraft’s autothrust and autopilot disconnected and multiple system alerts were generated. The captain took manual control of the aircraft and continued the climb to 20,000 ft, and levelled off to troubleshoot the issues and plan a return to Perth.
On approach to Perth Airport while aligning with the instrument landing system, the stall warning activated. The warning stopped after six seconds and the approach was continued for a successful landing.

The ATSB found the autothrust and autopilot disconnect was the result of erroneous airspeed indications during the take-off and climb due to blocked pitot tubes. The erroneous airspeeds were not detected by the pilots but had been detected by the aircraft’s systems, which had triggered the disconnect and generated multiple alerts including a ‘NAV ADR DISAGREE’ alert.

… it is important that alerts and procedures be designed to ensure that the pilots can correctly diagnose the source of the erroneous information…

This alert requires the pilots to crosscheck the three airspeed indications and assists them in determining if the source of the alert is an airspeed or angle of attack disagreement. However, limited space in the alert message area meant it was initially pushed off the screen for engine-related alerts programmed with a higher priority but in this case not requiring immediate action by the crew.  

The crew’s high workload meant the procedures for these alerts initially were not actioned and they were unable to address the ‘NAV ADR DISAGREE’ alert for about eight minutes, by which time the airspeed discrepancies had corrected themselves.
 
The ATSB found this sequencing of alert priorities and the alert’s associated procedure may have led the pilots to incorrectly identify the source of the alert as an angle of attack discrepancy, which the NAV ADR DISAGREE procedure advised had a risk of triggering an undue stall warning.
Combined with the multiple system alerts, which to the flight crew appeared to be unrelated, the flight crew thought the stall warning that activated during the approach was spurious and as such did not apply the stall recovery procedure. Stall warnings are triggered by angle of attack, not airspeed, and there were no indications that the angle of attack system was not functioning correctly.

ATSB Executive Director, Transport Safety, Mr Nat Nagy, said modern aircraft with multiple interacting systems can have many layers between the source information and the pilots. 

“The ATSB’s safety message from this investigation is where there is erroneous information from an information source, it is important that alerts and procedures be designed to ensure that the pilots can correctly diagnose the source of the erroneous information,” Mr Nagy said.
“Further, unless it is absolutely clear that it is erroneous, pilots should appropriately respond to stall warning alerts.”  

Airbus is currently in the process of updating the A320’s software so that the NAV ADR DISAGREE alert has a higher priority than the associated engine alerts. In the case of multiple alerts generated by unreliable airspeed, it will take precedence over the other associated alerts and be immediately visible to the pilots.

In addition, the ‘risk of undue stall warning’ message will be removed from the aircraft status related to the NAV ADR DISAGREE alert.
Read the report: Unreliable airspeed indication and stall warning involving Airbus A320, VH-FNP, near Perth, Western Australia
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Last update 04 April 2019

These were the safety issues identified: 

Priority of NAV ADR DISAGREE alert

Although the NAV ADR DISAGREE had more immediate safety implications relating to unreliable airspeed, the ECAM alert priority logic placed this alert below the engine-related faults. As a result, the NAV ADR DISAGREE alert was not immediately visible to the flight crew due to the limited space available on the ECAM display.

Safety issue detailsIssue number: AO-2015-107-SI-01
Who it affects: Operators of Airbus A320 aircraft
Status: Adequately addressed

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NAV ADR DISAGREE procedure

A NAV ADR DISAGREE alert can be triggered by either an airspeed discrepancy, or angle of attack discrepancy. The alert does not identify which, and the associated procedure may lead flight crews to incorrectly diagnosing the source of the alert when the airspeed is erroneous for a short period and no airspeed discrepancy is present when the procedure is carried out.
Safety issue details
Issue number: AO-2015-107-SI-02
Who it affects: Operators of Airbus A320 aircraft
Status: Adequately addressed

Strangely enough the date on these wet lettuce 'safety issues' is dated yesterday:

Eg:

Issue number: AO-2015-107-SI-01
Who it affects: Operators of Airbus A320 aircraft
Issue owner: Airbus
Operation affected: Aviation: Air transport
Background: Investigation Report AO-2015-107
Date: 04 April 2019

Yet under the title of 'Proactive Action' it states:

..On 10 August 2018, Airbus informed the ATSB that:

… after internal review with our ECAM specialists we have decided to increase the priority of the NAV ADR DISAGREE alert.

The NAV ADR DISAGREE alert will now have a higher priority than the EPR MODE FAULT alerts.

This will insure that in the event scenario, this alert would be directly visible to the crew.

This modification will be introduced in the next FWS [flight warning system] standard for SA family, the version F12, which currently planned for Q1-2019. A worldwide retrofit is anticipated...

Plus:

..On 23 January 2019, Airbus advised the ATSB that Airbus has launched the following safety actions:

1. The priority of the NAV ADR DISAGREE alert has been increased and will now have a higher priority than the EPR MODE FAULT alerts. In scenarios similar to the event, this alert will become immediately visible to the flight crew, therefore the detectability of a transient airspeed discrepancy will be significantly improved. It is recalled that the FCTM [Flight Crew Training Manual] presents this alert as one of the typical symptoms the flight crews must have in mind in order to detect this situation early and apply the "UNRELIABLE SPEED INDICATION" QRH [Quick Reference Handbook] procedure.

2. Following the full analysis of the AoA [angle of attack] failure cases leading to the triggering of the NAV ADR DISAGREE procedure, it was decided to remove the information line “RISK OF UNDUE STALL WARN” from the ECAM status. Indeed, it corresponded only to theoretical cases not considered as realistic in service. With this modification, if a flight crew determines the source of the NAV ADR DISAGREE alert to be an AoA disagree, the risk of undue stall warning will no more be present on the ECAM and therefore the flight crew will rely on the stall warning. This will address the risk of stall and loss of aircraft control mentioned by the ATSB in the Stall warning section of this report. This modification will be introduced in the FWS [flight warning system] standard F12, conjointly with the change of the NAV ADR DISAGREE alert priority.

3. Finally, Airbus will further enhance the detection of the unreliable airspeed situations with the introduction of the Unreliable Airspeed Mitigation Means (UAMM) function. In the event scenario, the ECAM should display the NAV ALL SPD UNCERTAIN red warning, which will request the ADR CHECK PROC / UNRELIABLE SPEED INDICATION to be applied. This function is intended to be introduced in forward fit in 2019 on the A320 Family, and will also be available for retrofit for eligible aircraft (a minimum computers configuration will be required).

The above extracts would seem to indicate that the ATSB identified these significant 'safety issues' long before yesterday?

Keep in mind that if, like most ICAO States with an AAI agency/entity, the ATSB had of issued safety recommendations to Airbus when the safety issues were first identified then Airbus would have been obliged to respond within 90 days - TSI Act reference:

 (2)  The person, association or agency to whom the recommendation is made must give a written response to the ATSB, within 90 days of the report being published, that sets out:

                    (a)  whether the person, association or agency accepts the recommendation (in whole or in part); and

                    (b)  if the person, association or agency accepts the recommendation (in whole or in part)—details of any action that the person, association or agency proposes to take to give effect to the recommendation; and

                    ©  if the person, association or agency does not accept the recommendation (in whole or in part)—the reasons why the person, association or agency does not accept the recommendation (in whole or in part).

            (3)  A person commits an offence if:

                    (a)  the person is someone to whom a recommendation is made in a report published under section 25; and

                    (b)  the person fails to give a written response to the ATSB within 90 days setting out the things required by paragraphs (2)(a), (b) and © (as applicable).

Penalty:  30 penalty units.

 

Ah yes once again the Hooded Canary's mob providing perfect topcover, while Airbus go about the business of patching up/covering up another potential airworthiness grounding - ie 'nothing to see here, all fixed, move along!'  

Now compare that to this from the Ethiopian AAIB:

 

2 INITIAL FINDINGS
On the basis of the initial information gathered during the course of the investigation, the following
facts have been determined:
 The Aircraft possessed a valid certificate of airworthiness;
 The crew obtained the license and qualifications to conduct the flight;
 The takeoff roll appeared normal, including normal values of left and right angle-of-attack
(AOA).
 Shortly after liftoff, the value of the left angle of attack sensor deviated from the right one
and reached 74.5 degrees while the right angle of attack sensor value was 15.3 degrees;
then after; the stick shaker activated and remained active until near the end of the flight.
 After autopilot engagement, there were small amplitude roll oscillations accompanied by
lateral acceleration, rudder oscillations and slight heading changes; these oscillations also
continued after the autopilot disengaged.
 After the autopilot disengaged, the DFDR recorded an automatic aircraft nose down (AND)
trim command four times without pilot’s input. As a result, three motions of the stabilizer
trim were recorded. The FDR data also indicated that the crew utilized the electric manual
trim to counter the automatic AND input.
 The crew performed runaway stabilizer checklist and put the stab trim cutout switch to
cutout position and confirmed that the manual trim operation was not working.

3 SAFETY ACTIONS TAKEN

The day of the accident, the operator decided to suspend operation of B737-8MAX.
On 14th March 2019, Ethiopian Civil Aviation Authority issued NOTAM regarding “The operation of
Boeing B737-8 ‘MAX’ and Boeing B737-9 ‘MAX’ aircraft from, into or over the Ethiopian airspace,
which is still active at the date of this report publication.

4 SAFETY RECOMMENDATIONS

 Since repetitive un-commanded aircraft nose down conditions are noticed in this
preliminary investigation, it is recommended that the aircraft flight control system related
to flight controllability shall be reviewed by the manufacturer.
 Aviation Authorities shall verify that the review of the aircraft flight control system related
to flight controllability has been adequately addressed by the manufacturer before the
release of the aircraft to operations.

Hmm...no further comment required (from me at least)  


However it is guaranteed there will be much MTF...P2