Spatial disorientation - S92 night rig take off

[CharlieOneSix]

From the Aberdeen Press & Journal 16 February 2024

CLOSE CALL: A Bristow S-92 helicopter, similar to the one involved in the incident.
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S92.jpg (13.78 KiB) Viewed 459 times

Pilots flying from an oil rig in the North Sea lost control of their helicopter for 40 seconds, air accident investigators have found. The Bristow S-92, which had nine passengers on board, lost altitude shortly after taking off from the Maersk Invincible in February 2020, and accelerated backwards at 56 miles per hour (49 knots).

Pilots lost control of the aircraft for 40 seconds – and regained it when the chopper was lower than the height of the helideck it departed from. A phenomenon called “spatial disorientation” which struck the first officer, and for a time the commander, has been cited by the Norwegian Safety Investigation Authority (NSIA) as the reason for the “serious incident”. NSIA said the take-off took place in “dark and challenging conditions” where the crew had no visual references, leading to the error.

It has recommended the regulator follow up with all operators on their Threat and Error Management systems, and made recommendations to Bristow regarding its helicopter pitch controls. At the time, the Maersk Invincible was based at the Valhall oil complex, about 180 miles south-west of Stavanger. The loss of control took place around one minute after takeoff.

NSIA said the first officer, who was at the controls, suffered a sensory illusion during the manual takeoff “as a result of the combination of head movement and both the vertical and horizontal acceleration”, which triggered “spatial disorientation”. That disorientation, accompanied by overcorrection of flight controls, then brought the helicopter out of position for its take off.

The aircraft’s pitch was a “high nose-up”, which NSIA believes led to the dramatic backward acceleration over 210 metres. For a period, the commander, who was pilot monitoring, also became disorientated. It was only when the commander made visual contact of the Maersk Invincible oil rig on the right side of the helicopter that he regained situational awareness and took over the controls.

It noted that this “spatial awareness” phenomenon can happen to all pilots, and occurs “more frequently when flying in bad weather or at night” due to limited visual references. NSIA said it believes there may have been “overcontrolling” of the cyclic force trim release button on the helicopter to correct its attitude (its orientation in reference to the horizon). Operator Bristow has since issued best practice guidelines to its pilots on the matter, which has been reviewed by the UK Civil Aviation Authority.

NSIA said the take-off took place in “dark and challenging conditions” where the crew had no visual references, leading to the error. Stabbing at the cyclic trim release is hardly going to help in that situation.

[probes]

NSIA said the take-off took place in “dark and challenging conditions” where the crew had no visual references, leading to the error. Stabbing at the cyclic trim release is hardly going to help in that situation.

"For a period, the commander, who was pilot monitoring, also became disorientated." How often does that happen?

[CharlieOneSix]

On my last type - 24 years ago - there wasn't a simulator in existence so on the airfield on an IMC base check under screens it was usual for the Training Captain to visually hover the helicopter and then hand over control to the candidate who then carried out a ‘night’ departure on instruments as he would from an offshore rig/platform in “dark and challenging conditions”. This involved a vertical climb to a decision point of 30ft above the helideck and then a rotation to 10 degrees nose down with climb power applied. This hopefully ensured you wouldn't clout the helideck with the tail if you lost an engine during the rotation. I always motored the cyclic trim 'hat' forward during the rotation – I never ever depressed the cyclic trim button as basically by doing that you remove any stabilisation in pitch and roll and make the whole thing more difficult as this crew found out.

So any offshore rig/platform take off in “dark and challenging conditions” without any horizon or depth perception available is really an IMC departure. I know nothing about the S92 or the new era of offshore helicopter types but no doubt they have a minimum IMC airspeed in the Flight Manual Limitations pages just as in my time. In my last type the minimum IMC indicated airspeed limit was 65kts with a proviso that climbing and accelerating under IMC was permitted from the VTOSS of 55kts to the minimum IMC airspeed of 65kts.

There is of course no way on a really black night offshore take off with no lights ahead of you that you can be anything other than on instruments from the moment you rotate at the 30ft decision point...yet the Flight Manual effectively prohibits such an action as you are of course below 55kts as you commit to IMC. There would have been no night operations to/from offshore rigs/platforms over the past 50 odd years had the IMC minimum airspeed limitation been applied. It was all accepted by the helicopter operators and I’ve even done it with CAA Flight Operations Inspectors in the other seat! One for the lawyers in the event of…….?

[Fox3WheresMyBanana]

Ah, the joys of the impossible rule that no one in authority will rescind but which they always ignore.

[Boac]

"For a period, the commander, who was pilot monitoring, also became disorientated." How often does that happen?

I'll attempt to answer your question. It helps if you understand how the body senses 'balance' and all the faculties it uses - a fascinating subject.

Suffice it to say that since people are 'built the same way', the disorientating effects of any movement will be felt by both pilots. The discipline of instrument flying is (should be!) strict in that in situations like a black night when there are no external visual clues as to what is happening, pilots are taught to rely on the instruments which are generally free from such disorientation, using different 'sensors' to humans to sense 'balance'.

The disorientating feeling can be extremely strong and pilots require a strong discipline to (mostly) ignore them and follow the instruments. In this incident both pilots would have felt the disorientating effects but it appears that the commander allowed these to over-ride his training and become disorientated. There are many reasons why the disorientating effects can be very strong, including tiredness and illness, and can accordingly be stronger for one member than another and one hopes one or more of any crew will use the correct procedure to cope with them. Single-seat pilots have to be even more 'disciplined' for obvious reasons to avoid filling a smoking hole.

[probes]

Thank you. Sounds scary. I've had to walk in a forest in pitch-dark, and even that was bad enough. Also lost the sense of 'horizon' while paddling in a flooded forest (for recreation) and it was hard to tell where the actual tree trunk ends and the reflection starts. But then one can be sure the vessel under you is where it is.

[Boac]

Indeed, but in 3 dimensional motion, sometimes there is no 'feeling' of the 'vessel' under you since you are experiencing reduced gravitational force on your feet, or zero or negative 'g' in some situations. The soles of your feet are a major balance 'organ' in our bodies, and interestingly the little toes are said to be an important indicator of lateral balance, and those who have lost the toes find difficulty in balance. It is a fascinating subject. If you are interested, read up on the 'semi-circular canals' in your head.

To go a stage further, a 'full-motion flight simulator' produces a feeling of acceleration or deceleration in the cockpit by tilting the whole shebang so you feel yourself pressed into your seat (or vice-versa) as you would in an accelerating vehicle. No 'acceleration' involved! The balance organs are simply 'confused'.

[CharlieOneSix]

Excellent explanations, Boac - better than I could do! Without a simulator part of our IMC base check included unusual attitude recovery whilst behind screens and keeping your eyes closed until the Training Captain finished his manoeuvring. A very worthwhile exercise and especially challenging if he left you in a zero 'g' situation. I recall one day many years ago being positioned by radar to the ILS in a single pilot S76 and I was asked to do a 360 orbit. I got very bad 'leans' as I straightened up from the orbit and it was a real fight to believe the instruments rather than my senses.

[Boac]

I well recall a USAF instructional film which was shown repeatedly to us during RAF flying training - black and white and I guess late 50's vintage, called 'Get on the gauges'. Very effective, and the simple message was 'Confused? - follow your instruments and not your head'. Worked for me. 'Leans' are awful, but the film message always struck home.

[Fox3WheresMyBanana]

We still got that film in the 1980s.

My worst case of the 'leans' was on Basic in the Jet Provost. I had to do a low level pull up in the Scottish mountains, when I came round a valley corner to find the rest of it full of snow squall.
It was surprising because there was supposed to be an instructor in another jet in front checking the weather was OK for me and another solo student.
However, he had pulled up earlier, and his call of doing so didn't reach us due to the geography. My oppo, being more sensible than I, had also gone home earlier.
It was also surprising because I pulled up from 300kts, but we had only done pull up training at 240 kts, and there was a lot more 'g' force involved at the higher speed.
Add in the really dark snow cloud and being in the middle of the highest mountains in the UK, and it was all very disorientating.
Once I got levelled at safety altitude, still in black, bumpy cloud, I changed the radio - by feel - to the Scottish Military frequency, but in the time it took to throw a quick glance at the radio to check, I looked back to find 60 degrees of bank on.
The level off had further screwed my internal gyros.
I spent the next minute doing nothing but looking at the Attitude Indicator and checking I was above safety height. Even the quick glances at the altimeter would throw off my attitude.
And my animal brain was screaming at me that I was going to die if I didn't align the aircraft with my internal gyros, and that little 4 inch instrument was telling me something else entirely.
So my hands were subconsciously moving the controls to get that internal alignment for every fraction of a second that I wasn't looking at the AI, but would do what they were told when I was.
Things finally settled down after a minute or two when my internal mental gyros realigned to believing that Straight and Level really was.
What really helped was my instructors having hammered in to me 'Power, Attitude, Trim'.
I just stuffed the throttle at a mid setting and left that to look after the airspeed. I also made sure I was trimmed at the times I had the aircraft stable.
It was thus mainly only bank angle that I had to fight to maintain.

Then, five minutes later, Air Tragic misidentified me and descended me back into the mountains IMC below safety altitude, but that's another story....

[Boac]

Cripes! I have just had to ask Mrs B to come and cut my slippers off my (retired) QFIs feet, so tightly were my toes curled after reading your story............. What sort of Basic Flying Instructor launches a 'Basic' solo student on a low-level navex in the Welsh/Scottish mountains with snow showers forecast? One who hates that particular student? One who doesn't understand? No, Sir! The idea of a weather ship checking the route has merit, but it foolishly assumes that bloggs is on the right route................... (or , of course, that the QFI is....)

I will tell a tale here. I had a Cranwell student, no doubt future CAS material (of course) on a dual low-level sortie in the Yorkshire hills. Fully briefed on the importance of not losing sight of the ground 250' below him and what to do if he did. We flew gently on, heading towards rising ground which disappeared into cloud a bit further up. Like all (good) QFIs I allowed bloggs to continue, to watch his decision making ability. Inevitably we began to enter cloud on the upslope of the hill. A microsecond passed while I awaited the emergency pull up, but no, he pushed forward to go back down.............. I was told we had one of the few Jet Provosts with an 'S' shaped control column We did pull some 'g' then. That future CAS got sent, I think, to Nav training not long after.

[Fox3WheresMyBanana]

I thought you might ask about 'the plan'.
We were on detachment to Kinloss for low level navexs, and running out of time. Going back to Cranditz without completing the student solos would involve reflying duals, running out of time back at base also, etc.
The plan was for an instructor to fly ahead, then two students at 2 minute intervals, yours truly being Tail End Charlie. All the instructors on duty agreed to the plan. Both students were considered sensible and indeed both subsequently made it to front line Tornados. And I won the Nav Trophy and the other guy was second, so neither of us had got lost so far or were likely to.
Unfortunately, the instructor in the lead decided to call it off not long into the sortie, when he was in the Great Glen but we were not yet in it. Then when he tried to contact us again, he was out of it and we were in it.
My oppo pulled out a few minutes later, of his own choice, but didn't make any radio calls till he was out of the Great Glen, so I didn't hear him either.
So, of course, I was pressing on thinking a sensible instructor and a sensible course mate were in front of me and thought it was OK. I got about three quarters of the way round before pulling up.
The instructors obviously had a big debrief afterwards, and it was worked out that there had been only a narrow window of less than a minute when the inability to hear the calls by both students existed, but life being what it is, that is when it had happened.
The snow squalls were not, ISTR, forecast, or at least not for our route (I was on track throughout). This meant there were several aircraft pulling up from low level at about the same time in the same area, and what consequently led to the misident. I believe it was a Jag OCU jet trying to recover to Lossie they confused me with.
So, just one of those things. Or rather, two of them.

Kinloss, being Kipper Fleet, had a 24 hour scruff's bar. First and only time I've had a second breakfast of several beers at twenty past eight in the morning. The auth, the lead instructor, and my oppo all joined me.

p.s. The lead instructor had been a Canberra man back when they had the nuke role in Germany, so was well used to low level in scoshie wx. It All Seemed Like A Good Idea At The Time.

[Boac]

The detachment commander was a lucky man!

[Fox3WheresMyBanana]

The detachment commander was the lead instructor.

Anyway, back to disorientation.
I would think that it is likely to be worse in a helicopter, since there is a higher level of general vibration, and that hovering gives more opportunities to misinterpret what is happening, since going backwards (as happened in the above example) is a possibility. There seem to be a remarkable number of accidents when snow or sand cause instant loss of visual references on take-off or landing. Probably smoke too, thinking of G-man's environment.
Any instant dust clouds happen to you in the Harrier, BOAC?

[Boac]

No, never went anywhere with dust in the bonajet.