(05-06-2017, 08:56 AM)kharon Wrote: Tactful of toothless?
Hi Sidebar; welcome. We too are waiting (quite a long wait) for the Pel-Air report. It promises to be an ‘interesting’ study piece. My ‘tote’ board has a record number of entries and, the written forecast results are very ‘entertaining’. Top money is for release on or about ‘Budget’ day. We shall see. But today we have the ATR incident to consider.
The ATSB report, although a long time arriving, is better stuff. This is what we may expect from a ‘deep’ investigation with the manufacturer involved and confirmation from the UK supports the ATSB conclusions; however. Do the SR’s make good sense? Are you prepared to by-pass the radical causes?
ATSB: “The pitch disconnect occurred while the crew were attempting to prevent the airspeed from exceeding the maximum permitted airspeed (VMO)”.
ATSB – “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.”
But what of the crew actions which had the aircraft at ‘red line’, the conflicted elevator inputs which created the disconnect of the elevator channels and subsequent damage, caused by operations outside the ‘certified’ design envelope? Why are these elements not examined, in detail, before questioning the ‘integrity’ of the manufacturer and the certifying agency?
Limitations and certification tests, must, if aircraft are to fly, have ‘limits’ and then a ‘buffer’ about those limits which can be ‘reasonably’ supported. Simplistically put, an egg is ‘designed’ and tested to withstand certain anticipated loads, if it is a government certified egg, then if will be required to withstand that load + a ‘reasonable %’ more. Used correctly, your egg will last, throw it a wall with no more than that % above ‘test’ all is well. Go past that limit and you have a clean up job to do. The point I’m trying to make is if an airframe is ‘thrown’ at a wall, above the limitations imposed, something will break. The ATR is a proven, might tough airframe; the fact that it failed to ‘break’ during the initial incident and continued operations for quite a while afterwards, speaks well for design and certification standards. What is not being addressed by the ATSB is ‘how’ the initial damage was done; and, what caused it. Why is this element being so carefully stepped around? ATR cannot continue to increase allowable limits to an infinite value, on ATSB say so. It is an aircraft, not the harbour bridge.
I did at one time do the research into the force required to ‘separate’ the control channels; can’t find it now, but it was a significant number i.e. you have to really mean it. One pulls back, the other pushes forward, the clutch disengages and you have independent elevator controls. So, somehow, even accidentally, the conflicting crew ‘actions’ have managed to not only separate the control channels, but, through opposing forces, imposed a greater load on the airframe than certification design specifications.
There may well be a ‘design’ and ‘certification’ weakness; but provided the aircraft met the certification requirements, as specified, and has been proven to exceed those specification through ‘hard’ use, then is it fair to question the integrity of the aircraft – as presented?
Another troubling part of this ATSB report is the lack of FDR and CVR data. I, for one, would very much like to know exactly what occurred on the flight deck and see the exact data provided by the FDR. In particular, the pitch channel and speed data for the entire sector. I wouldn’t mind seeing the original written reports from both aircrew and engineering either.
Vitesse (not velocity) Maximum Operating. (Vmo). Maximum Operating limit speed. Red line…
FAA - The pilot should be aware of the symptoms that will be experienced in the particular airplane as the VMO or MMO is being approached. These may include:
• Nose-down tendency and need for back pressure or trim.
• Mild buffeting as airflow separation begins to occur after critical Mach speed.
• Activation of an over-speed warning or high speed envelope protection.
Personally, I can’t remember ever pushing an airframe to the ‘red line’ as a regular practice; often close, but not deliberately to, for several reasons; gas for Mum, speed for the kids and height for my own peace of mind is always in the flight bag. I digress.
When this incident occurred, there were some good post on the UP related (some rubbish as well) but for those who would like to take their thinking beyond the narrow confines of the ATSB report; start –HERE -.
Good, but incomplete, ATSB marked 4 out of a possible ten, which is much better than the usual 1 or 2 they struggle to win. Although the following, carefully read, is a typical, ATSB conflicted nonsense.
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.
To what limits? It already meets the prescribed and proven better, so, what's the point?
For analysis of the inflight situation, ATR has used the aerodynamic model that was developed during certification. Preliminary results for the jamming scenarios was provided. Those results showed that the inflight system response is also that of an underdamped oscillatory system. It also indicates that the magnitude of the system response is dependent upon the pilot input to the control column, and how quickly the flight crew respond to PUM activation. The system has margin for jams at the elevator. ATR are continuing the analysis of jams at the control column.
Again, how long is a piece of string? Is it a King Kong v Faye Wray tussle or two average pilots pulling and shoving? Balanced, I don't think so.
The ATSB acknowledges the efforts of ATR to resolve the safety issue. The ATSB also notes that, while the short term risk assessment does not account for the transient elevator deflections associated with a pitch disconnect, until the results of the detailed engineering analysis are available it is not possible to accurately quantify the transient elevator loads. Consequently, it is not possible to fully determine the magnitude of the risk associated with continued operation of ATR42/72 aircraft until the engineering analysis is complete.
Noting the above, the ATSB’s retains a level of ongoing concern as to whether the aircraft has sufficient strength to withstand the loads resulting from a pitch disconnect. Consequently, while the ATSB accepts that the current level of safety action partially addresses the safety issue; the ATSB makes the following safety recommendations.
Somebody, anybody, please: explain what that last load of double speak bollocks means.
Toot – sigh – toot.
Recent media coverage on ATSB ATR 2nd interim report.
Via FlightGlobal:
Quote:ATSB airs safety concerns on ATR pitch controlsVia Asiacruise news:
The Australian Transport Safety Bureau (ATSB) has called on ATR to quickly complete an engineering assessment of the type's pitch control system, amid possible concerns that a serious design flaw may be present in the ATR 42 and 72 series.
- 05 May, 2017
- SOURCE: Flightglobal Pro
- BY: Ellis Taylor
- Perth
The recommendation was made in the Bureau's second interim report into a 2014 incident in which the crew of a Virgin Australia ATR 72-600 (VH-FVR) made strong opposite inputs to the pitch controls, leading to a 'pitch disconnect', which uncoupled the left and right controls to the elevators.
This resulted in potentially catastrophic damage to the aircraft's horizontal stabiliser, while a cabin crew member was seriously injured by the aerodynamic loads generated during the event. However, the damage was not detected for five days, after which the aircraft was grounded for several months before returning to service.
In the earlier phases of its investigation, the ATSB identified that "transient elevator deflections during a pitch disconnect event that could lead to aerodynamic loads that could exceed the strength of the aircraft structure."
An interim report released by the Bureau in June 2016 identified that the opposite control inputs were "not part of normal procedures", but added that "the existing procedural risk controls alone may not be sufficient to prevent this type of occurrence".
The ATSB's second report follows greater analysis of ATR's design for the pitch control mechanisms and their performance during a pitch disconnect event.
It found that flexibility within the pitch control system cables led to a rebalancing of loads in the system following the activation of the pitch uncoupling mechanism, and "dynamic transient elevator deflections" shortly after the mechanism was activated.
It also found that there was "unavoidable movement of the control column(s)" after the mechanism had been activated.
"Each of these effects may contribute to elevator deflections greater than the aircraft manufacturer considered during the design and certification of the aircraft," the ATSB adds.
In December, ATR undertook an assessment of the short term risks with the system. This concluded that the system was safe as the ultimate loads could not be exceeded through the control column, and that the probability of a similar event happening was low.
Nonetheless, in January FlightGlobal reported that ATR planned to update the operating manuals of its aircraft to warn pilots of the risks involved in making large flight control inputs.
The manufacturer is also undertaking a detailed engineering analysis using an analytical model backed up by ground and flight testing. Further modelling of dual input scenarios and flight testing is being carried out, in association with the European Aviation Safety Agency (EASA), which is the certifying authority for the aircraft.
"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," the report says.
The ATSB has also called on EASA to monitor and review the engineering analysis to determine if the aircraft can withstand loads resulting from a pitch disconnect.
"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," it adds.
Quote:Threat To ATR Turboprops Concerns Australian Investigators.
05 May 2017
Safety recommendations issued to manufacturer and regulators as a result of investigation into serious Virgin Australia incident.
>
ATSB images showing damage to the ATR72's tail.
Australian air safety investigators are worried a repeat of a damaging incident that crippled a Virgin Australia ATR72 turboprop in 2014 could lead to another aircraft suffering significant structural damage.
The February 20, 2014, incident occurred when two flight crew attempting to slow the ATR 72 aircraft during descent into Sydney inadvertently applied opposing control inputs and triggered a “pitch disconnect’’. This resulted in serious damage to the aircraft’s tail and injured a senior cabin crew member.
However, the plane was initially thought to have experienced “moderate turbulence’’ and flew for several days, despite a visual inspection by an engineer, before the severe damage to the tail was detected and it was grounded on February 25.
Pitch is controlled by pilots pushing and pulling on the control column to lower or raise the aircraft’s nose. By moving the horizontal panels on the aircraft’s tail, or elevators.
The elevators normally move in the same direction and in equal amounts but there is a mechanism, the pitch uncoupling mechanism, which allows them to operate independently in the event one jams.
By pushing the control columns in opposite directions, the Virgin pilots activated this mechanism and subjected the aircraft to stresses it was not designed to take.
Australian Transport Safety Bureau continued to investigate the incident and discovered there are momentary elevator deflections during a pitch disconnect that could lead to aerodynamic loads capable of exceeding the design strength of the aircraft.
They also discovered these transient elevator deflections had not been identified when the aircraft type was originally certified.
The ATSB was sufficiently concerned about the potential impact to put out a second interim report making three recommendations.
It has asked ATR to complete an assessment of the safety issue as soon as possible to determine whether the aircraft can safely withstand those loads.
It has also asked the European regulator, EASA, and the Australia’s Civil Aviation Safety Authority to review ATR’s engineering assessment “and take immediate action if the analysis the aircraft does not have sufficient strength’’.
“Our concern is that, given the design of the ATR42 and ATR72 aircraft, opposing control inputs can result in aerodynamic loads that may exceed the design strength of the tail structure, causing significant damage," ATSB chief commissioner Greg Hood said.
"Since we identified this issue, our aeronautical and structural engineers have conducted extensive analysis based on additional data provided by ATR. The findings of that analysis, supported by an independent peer review from the UK Air Accidents Investigation Branch, confirmed our initial concerns."
ATR is continuing to conduct further engineering analysis of the issues raised by the ATSB and Australian operators of ATRs, Toll Aviation and Virgin Australia, have taken action to minimise the chances of the situation reoccurring and to train pilots to manage it if it does.
Virgin said Friday it was confident the risk mitigation procedures it had introduced meant the aircraft remained suitable for operations.
“Safety is Virgin Australia’s number one priority, and we continue to liaise closely with the relevant regulatory bodies and the aircraft manufacturer in relation to the Australian Transport Safety Bureau’s ongoing investigation into the ATR’s pitch disconnect mechanism,’’ it said in statement emailed to AirlineRatings.
EASA’s initial response was to issue a safety information bulletin which said it did not consider the problem an unsafe condition that would warrant an Airworthiness Directive.
CASA said it was closely monitoring the ATSB investigation.
“CASA continues to audit ATR aircraft operators to ensure appropriate actions have been taken to reduce the likelihood of the aircraft being mishandled in a manner similar to the incident flight,’’ it said.
“Flight procedures and pilot refresher training for the ATR aircraft operated in Australia have been amended since the event occurred.
“CASA will look carefully at the findings of the aircraft manufacturer’s engineering analysis of the issues associated with a pitch disconnect when this work is completed.
“If this analysis raises any ongoing safety issues CASA will take appropriate action. CASA will take into account any measures taken by EASA. ‘’
ATR said: "In conjunction with EASA, ATR is completing the assessment of transient elevator deflections. Via the BEA, ATR continues to provide assistance to the safety investigation conducted by the ATSB."
The investigation into the Virgin incident is continuing.
Source : http://www.airlineratings.com/news.php?id=1214
MTF...P2
