[Peetwo]

Twenty five years; four tails; 478 funerals; a birdstrike; and a broken leg - Part I     

When you Google "longest aviation accident investigation ever" the top of the page comes up with this NTSB link:

NTSB Concludes Longest Investigation in History; Finds Rudder Reversal was Likely Cause of USAIR Flight 427, A Boeing 737, Near Pittsburgh in 1994. ... Theflight was arriving from Chicago. All 132 persons aboard - 127 passengers and 5 crew - perished in the crash.

https://www.ntsb.gov/news/press-releases...737_N.aspx

Now I am not sure if with the publishing of the final investigation report into US Air flight 427 on the 24 March 1999, if the NTSB actually holds the world record for the longest completed AAI but yesterday the 4 year 6 month 17 day investigation was well and truly pipped (5 years 3 months 5 days i.e. 261 days) by our very own Hooded Canary led ATSB with the release of the FR into the 20 February 2014 broken tail ATR accident...   

This is the ATSB presser:

ATSB issues recommendations for improved aircraft design tolerance to inadvertent dual control inputs
The Australian Transport Safety Bureau has issued Safety Recommendations to the European Aviation Safety Agency (EASA) and aircraft manufacturer ATR seeking improved aircraft system design tolerance to inadvertent dual control inputs by pilots.



The Safety Recommendations are contained in the ATSB’s final investigation report into an inflight upset and inadvertent pitch disconnect experienced by an ATR 72 turboprop airliner on a flight from Canberra to Sydney in 2014.

During that flight, as a result of a sudden decrease in tailwind, the ATR’s pilots unintentionally applied opposing control inputs to their control columns while trying to ensure the aircraft remained below its maximum operating speed. These differential forces activated the aircraft’s pitch uncoupling mechanism. Intended for activation in the event of one of the aircraft elevators being jammed, the pitch uncoupling mechanism resulted in a pitch disconnect, where the elevators could operate independently of each other.

With the pilots applying opposing control inputs and built-up tension within the flight control system, the pitch disconnect resulted in transient asymmetric elevator deflections, generating aerodynamic loads that exceeded the strength of the horizontal stabiliser (tailplane), causing significant damage.

The aircraft landed safely and was inspected by maintenance engineers but the damage was not detected. The aircraft returned to service and operated a further 13 flights before a subsequent inspection after a suspected birdstrike found it had sustained serious structural damage to its horizontal stabiliser, which was subsequently replaced.

Discovery of that damage was the catalyst for one of the ATSB’s most complex, thorough and protracted safety investigations.

Through the release of two interim reports, the investigation has already seen the aircraft manufacturer, aircraft operator and aircraft maintenance provider address a number of safety issues identified by the ATSB.

However, as part of its final report, the ATSB has issued a Safety Recommendation to EASA, recommending taking “further action to review the current design standard (CS-25) in consideration of effect that dual control inputs may have on control of aircraft.”

In addition, the ATSB has issued two Safety Recommendations to aircraft manufacturer ATR, recommending that ATR:

• assess the operational risk associated with limited tactile feedback between left and right control columns in the context of no visual or auditory systems to indicate dual control inputs; and
  
• perform a detailed review of the effects of dual control inputs on the aircraft’s longitudinal handling qualities and control dynamics to determine if there are any detrimental effects that could lead to difficulty in controlling the aircraft throughout the approved flight envelope and operational range.
  

“What this report seeks to achieve is to influence further incremental safety improvements,” ATSB Chief Commissioner Greg Hood said.

Aircraft and aircraft systems need to be designed in anticipation of and tolerant to foreseeable inadvertent flight crew actions.

“This serious incident demonstrates aircraft and aircraft systems need to be designed in anticipation of and tolerant to foreseeable inadvertent pilot actions.

“Further, when identified, aviation safety regulators and aircraft manufacturers need to address previously unforeseen aircraft design consequences during the operational life of an aircraft type.”  

Mr Hood said the investigation also highlights the importance of a full and proper inspection to detect aircraft damage and the need for the inspection to be fit for purpose and for inspections to be coordinated and certified to avoid a single point failure.
“The ATSB looks forward to EASA’s and ATR’s responses to our Safety Recommendation from this investigation.”

Read the report AO-2014-032: In-flight pitch disconnect involving ATR 72 aircraft, VH-FVR, 47 km WSW of Sydney Airport, NSW on 20 February 2014
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Last update 24 May 2019

Spot the disconnects (pun intended -   )??

Perhaps this will help?

Via FR:

Based on the crew report of an in-flight pitch disconnect associated with moderate turbulence, and data recorded by the aircraft’s on board maintenance systems, VARA maintenance watch arranged for the contracted approved maintenance organisation, Toll Aviation Engineering, to carry out the applicable maintenance. However, the licenced aircraft maintenance engineers involved in the Inspection after flight in turbulence and/or exceeding VMO did not carry out the specified general visual inspection of the stabilisers probably because of a breakdown in the coordination and certification of the inspection tasks between the engineers. The damaged horizontal stabiliser was not detected and the aircraft was released to service...

VH-FVR under tow following completion of post-occurrence maintenance. The angle of the horizontal stabiliser relative to the angle of the wings indicates substantial structural deformation.


Source: Sydney Airport

During the next 5 days the aircraft was operated on 13 flights and was subject to routine walk‑around visual inspections by flight crew and engineers. No one identified any anomalies until flight crew observed some damage after a suspected bird strike. The aircraft was grounded and subjected to extensive maintenance that included replacement of the horizontal and vertical stabilisers.

Upper tailplane of VH-FVR showing damage to horizontal and vertical stabilisers that was evident when the damage was identified 5 days and 13 flights after the in-flight upset/pitch disconnect and associated maintenance

Note that the Hooded Canary indicates that both ATR and EASA were issued with the same SR. What he neglects to say is that same SR was also issued to CASA:

Consideration of transient elevator deflections from a pitch disconnect 
Safety issue number: AO-2014-032-SI-02
Safety issue description: The aircraft manufacturer did not account for the transient elevator deflections that occur as a result of the system flexibility and control column input during a pitch disconnect event at all speeds within the flight envelope. As such, there is no assurance that the aircraft has sufficient strength to withstand the loads resulting from a pitch disconnect.

Safety recommendation to ATR
The ATSB recommends that ATR complete the assessment of transient elevator deflections associated with a pitch disconnect as soon as possible to determine whether the aircraft can safely withstand the loads resulting from a pitch disconnect within the entire operational envelope. In the event that the analysis identifies that the aircraft does not have sufficient strength, it is further recommended that ATR take immediate action to ensure the ongoing safe operation of ATR42/72 aircraft.

Safety recommendation to the European Aviation Safety Agency
The ATSB recommends that EASA monitor and review ATR’s engineering assessment of transient elevator deflections associated with a pitch disconnect to determine whether the aircraft can safely withstand the loads resulting from a pitch disconnect within the entire operational envelope. In the event that the analysis identifies that the aircraft does not have sufficient strength, it is further recommended that EASA take immediate action to ensure the ongoing safe operation of ATR42/72 aircraft.

Safety recommendation to the Civil Aviation Safety Authority
The ATSB recommends that CASA review ATR’s engineering assessment of transient elevator deflections associated with a pitch disconnect, to determine whether the aircraft can safely withstand the loads resulting from a pitch disconnect within the entire operational envelope. In the event that the analysis identifies that the aircraft does not have sufficient strength, it is further recommended that CASA take immediate action to ensure the ongoing safe operation of Australian‑registered ATR42/72 aircraft.

 
This is part of the weasel worded response to that SR from CASA:

...CASA advised that since 10 February 2016, they have been involved in a comprehensive dialogue with ATR and EASA regarding the assessment of the transient elevator deflections associated with pitch disconnect to address this safety recommendation. CASA has also engaged with the ATSB throughout the investigation. CASA provided an interim response to the ATSB safety recommendation on 15 June 17. CASA intends to provide a further response to the ATSB safety recommendation following the release of the final report. That response, in part, depends on EASA’s response to the same safety recommendation...

Remember again that this accident occurred 1921 days ago - 

TBC...P2