Inadvertent dual control inputs led to undetected damage

2712
Source: ATSB

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 for inadvertent dual control inputs by pilots after an incident in 2014.

On 20 February, a Virgin Australia ATR 72 aircraft took off from Canberra en route to Sydney. While passing through 8500 feet, the aircraft encountered a sudden decrease in tailwind. This led to a rapid increase in airspeed, with the primary flight display likely indicating well above the maximum operating speed (VMO) of 250 knots. The first officer (pilot flying) reduced engine power and made nose-up control inputs in an attempt to slow the aircraft.

Simultaneously, the captain (pilot not flying) took control of the aircraft and made nose-up pitch control inputs without following the specified take-over procedure and alerting the first officer of his intent. Shortly after the captain initiated the nose-up control inputs, the first officer (unaware that the captain was also making control inputs) reversed his control input. The differential forces in the left (captain) and right (first officer) pitch control systems reached the threshold to activate the pitch uncoupling mechanism, disconnecting the left and right pitch control systems from each other.

The captain completed the take-over by announcing he had control about five to six seconds after taking hold of the controls. However, before the take-over procedure was completed, the addition of the captain’s and first officer’s nose-up control inputs resulted in a pitching manoeuvre that exceeded the limit load factor for the aircraft.

A cabin crew member was unrestrained in the rear of the cabin and when the aircraft pitched back down, she was thrown from her seat and suffered a broken leg.

The flight crew continued the flight using one of the pitch control systems and landed safely in Sydney. It was inspected by maintenance engineers, but no damage was 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 as a result of the 20 February incident.

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

ATSB Chief Commissioner Greg Hood said, ‘This serious incident demonstrates aircraft and aircraft systems need to be designed in anticipation of and tolerant to foreseeable inadvertent pilot actions. Aviation safety regulators and aircraft manufacturers need to address previously unforeseen aircraft design consequences during the operational life of an aircraft type.’

Hood said the investigation also highlighted 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.

11 COMMENTS

  1. Five years to produce this is a disgrace! We ought to be ashamed of ourselves for being so inept, but I guess this is Australia, a country not known to do anything efficiently or effective !

  2. Interesting that there is so much focus on the mechanical damage, and very little on the management failure that created the situation leading to damage. Surely the need for formal handover of control should have been emphasised? How many times will we keep seeing incidents arising from poor cockpit management and culture?

  3. Walter, i am quite sure Australian operators of the ATR were made aware of the issue before the report was published. It is understandable that the captain instinctively reacted to a dangerous situation. The controls need to be fool proof. Imagine that happening in a C182? Impossible

  4. One pilot flies the aircraft at any one time.If the other pilot wants to fly it calls : “my aeroplane”, the other pilot replies : “handing over” and releases the controls.

  5. Everyone is too worried about a minor speed excursion on Vmo. You don’t “die “ when an aircraft overspeeds by a few knots. The rush to control the overspeed and incorrect takeover procedures … let’s go back to basics and not try and engineer a fix ! I bet dive speed Vd / Vne on the ATR is well over 300 knots really. But I’m guessing.

    • A/C are tested to well over their intended day to day operating speeds so as to protect the occupants onboard. I believe B747 was taken to Mach 0.99 during certification, oh what fun. Much like the SWL on cranes etc usually over engineered by 50%. Remember when mankind designs/builds a anything there will be those who will find its limits! On yr other note you are correct, us pilots are more concerned about the “just culture” within the big operators when a pilot inadvertently goes beyond a limitation, punitive actions first, why second, such is the industry we operate in.

  6. A hat trick – of warnings.

    There are two ‘deep’ elements which ATSB have not deigned to cover off. Esoteric some would say; others would say it belonged to the new generation; some would consider company culture; there are some who would tag the observations as ego and attitude. To me, the elements above weave a pattern where airmanship, training and experience have been lost in the ‘hype’.

    One can, and there is evidence supporting (BA for example) where the ‘problem’ begins with the HR folk. A cardboard cut out of the ideal crew – for company purposes – a ‘type’ if you like. You can, with almost 100% accuracy go to a pub and identify the company the individual’s fly for: won many a beer playing this game. There is little in the way of variation; which, for company purposes, is great. Not so much for having the right stuff somewhere on the flight deck. But, IMO it is a flawed philosophy – good pilots ain’t always ‘good’ corporate citizens – compliant and biddable; nor easily intimidated. A small, but important thread in the pattern.

    P2 – The aircraft was descending through heavy rain when the right engine flamed out, automatically re-starting within five seconds as it is designed to do. As the descent continued the left engine also flamed out, automatically relighting as before with the right engine

    To me this is tale is a warning flag; an indicator of pilot training and thinking error. “descending through heavy rain” – Why was the ‘spark’ not selected to manual (ON) before entering ‘heavy rain’. It should be an automatic action to turn the crackers on – long before entering; same as the icing gear – get it hot and working before – basic common sense. Training, corporate or pilot error? It costs maintenance money to replace the ‘crackers’ – but be buggered if I’d sit and wait five seconds for a relight even once – let alone twice. It took two flame outs before the crew selected ‘ON’. Tea and biscuits on my watch for that crew.

    P2 – A hard landing in turbulence on 19 November 2017 resulted in substantial damage to a Virgin Australia ATR 72-600, say investigators in a preliminary report.

    We have all done it – thumped one on – hard. Quartering crosswind sneaking in behind; strong gusty conditions etc. But you really need to mess it up to damage an inherently tough airframe. You can – even OEI go around from a very low height – you can also ‘feel’ when the aircraft has become a well trimmed manhole cover and take preventative action; maybe you ‘bang’ it on – but you don’t break it.

    P2 – A search of the VARA occurrence database for over speed events from 2012 to 2014 identified seven occasions where an ATR 72 crew reported a VMO over speed event on descent.

    Speed excursions happen – not very often – certainly not with this monotonous regularity. Particularly during a descent phase. There is a great deal of difference between a professional assessment of the conditions and the descent profile being ‘worked’ to suit the ambient conditions, than simply programming the Auto to get you to 1500 feet at five mile from Kickinatinalong. Lots of time spent ‘discussing’ and ‘briefing’ the approach plate – but little on the conditions expected throughout the ‘descent’ phase. Over speed is a training and airmanship matter.

    Seasoned, thinking pilots will understand the need to manage the whole process so as not to over speed the aircraft and wind up with a hard landing after two flame outs before selecting continuous ignition approaching in heavy rain. These three known items may not be potential killers – but by Golly, they are man made holes in that famous Swiss cheese. How this becomes a matter for ATR to solve is beyond my ken; this, before we even get to the meat and spuds of how the control channels became separated in fairly routine conditions between Canberra and Sydney; and, how ATR are expected to re-jig their aircraft to prevent terminal stupidity. More to follow – you can bet on it.

    Aye well – back to my knitting. Before I do :-

    Cute as a button. Or; funny coincidence department? – You pick. Either way it is a classic of ATSB aberrations; all part of being the PR extension for the big guns. I’m rattling on about the exquisite timing of the ATSB release of the long awaited report into the badly damaged ATR. Go figure the odds; five years and change we waited for the release and when does it happen?

    Apart from Cready and Oz Aviation – the media completely missed this one; and, there is a story there, a scary one to boot. But what with the world watching the Moscow tragedy and the 737 Max brouhaha and some kind of conference; and, a federal election on the boil – ATSB choose this particular time to quietly slip this report into he public arena. Thing’s that make you go Hmm indeed.

Leave a Reply to Simon philip bromiley Cancel reply

Please enter your comment!
Please enter your name here