2018 Helicopter Tragedy - Investigation Outcome/Verdict Released

[Wymsey]

Edit: Apologies, the full article is behind a pay wall.

 

Edited 5 September 2023 by Wymsey

[Tuna]

Report is here

 

https://www.gov.uk/aaib-reports/aircraft-accident-report-aar-1-slash-2023-leonardo-aw169-g-vskp

[HankMarvin]

A catastrophic failure of the rear rotor mechanism was the cause of the helicopter crash outside King Power Stadium that killed five people, including Leicester City chairman Vichai Srivaddhanaprabha, a report has determined.

The Air Accidents Investigation Branch (AAIB)’s final detailed report into the tragedy, which also claimed the lives of pilots Eric Swaffer and his girlfriend, Izabela Lechowicz, plus members of Khun Vichai’s staff, Kaveporn Punpare and Nusara Suknamai, on October 27, 2018, is published today.

The report states there was “seizure of the tail rotor duplex bearing” which initiated a sequence of failures in the tail rotor pitch control mechanism, sending the Leonardo AW169 into an uncontrollable spin, or yaw, which was impossible to recover.

The helicopter had climbed to 430 feet as it left the centre circle of the stadium at 7.37pm following Leicester’s 1-1 home draw with West Ham Unitedwhen Swaffer lost control as he began to try to turn right towards the direction of travel. Despite Swaffer applying all the corrective control inputs, the unstoppable spin began and the aircraft began to descend.

Even in an uncontrollable spin and in darkness, Swaffer tried to cushion the landing at 75 feet by raising the collective, the control that determines lift, but the helicopter landed on a stepped concrete surface, which made it come to rest on its left side.

A summary of the report said: “The impact, which likely exceeded the helicopter’s design requirements, damaged the lower fuselage and the helicopter’s fuel tanks which resulted in a significant fuel leak. The fuel ignited shortly after the helicopter came to rest and an intense post-impact fire rapidly engulfed the fuselage.”

Fans pay tribute to Vichai Srivaddhanaprabha (Photo: Shaun Botterill/Getty Images)

The investigation found that flight survey test results by the helicopter manufacturers were not shared with the manufacturers of the tail rotor duplex bearings which failed to assess their suitability, or that the manufacturer did not implement a routine inspection requirement for critical part bearings removed from services for review, but the report noted in both cases the manufacturer were not required to by the regulatory process.

The report also noted there were no design or test requirements that specifically tested for “rolling contact fatigue” in the bearings identified as critical parts and “while the certification testing of the duplex bearing met the airworthiness authority’s acceptable means of compliance, it was not sufficiently representative of operational demands to identify the failure mode.”

The report also identified failings in possible risk assessment and mitigation measures within the wider tail rotor control system not fully considered in the certification process, but that the regulatory guidance stated that this was not required.

The investigation involved a multi-disciplinary team of skilled investigators from the AAIB, supported by a wide range of experts from industry, academia, and safety investigation authorities from around the world, and identified the failings on the craft as well as making eight recommendations to the European Union Aviation Safety Agency to avoid future tragedy.

The recommendations include validation of design data by suppliers post-test; premature rolling contact fatigue in bearings; life limits, load spectrum safety margins and inspection programmes for critical parts; and assessment and mitigation of catastrophic failure modes in systems.

“This was a tragic accident in which five people sadly lost their lives,” said Crispin Orr, the chief inspector of Air Accidents. “Our thoughts are with their loved ones, and everyone affected.

[MPH]

I kind of clung to the hope no one was scared or knew what was about to happen 

 

[Sly]

In essence, with the bearing failure in the rotor then, this was an accident waiting to happen. 
 

What I am surprised by and I’m sure that some of the more production or engineering members of the forum would be better placed to comment on, can you not hear a difference when bearings begin to fail? 

[AmyLGK]

"The recommendations include validation of design data by suppliers post-test; premature rolling contact fatigue in bearings; life limits, load spectrum safety margins and inspection programmes for critical parts; and assessment and mitigation of catastrophic failure modes in systems."

 

Im shocked these weren't already in place for such a critical component 😮

 

[AmyLGK]

Oh no, there is a daily mail article which goes into more personal details of the event 😢

[chapero82]

So 4/5 survived the impact 😢 I was hoping they didn’t suffer 

[st albans fox]

55 minutes ago, chapero82 said:

So 4/5 survived the impact 😢 I was hoping they didn’t suffer 

We can only hope that those four were  unconscious after the impact and were aware of nothing thereafter 

[An Away Move]

Reported in The Guardian too,

 

https://www.theguardian.com/world/2023/sep/06/helicopter-crash-leicester-stadium-tragic-accident-inspectors

 

So sad to hear the last exchanges between those onboard and that the pilot did everything right, but had no idea what was going on. Crazy that wear to a ball bearing caused it.  

[An Away Move]

2 hours ago, Sly said:

In essence, with the bearing failure in the rotor then, this was an accident waiting to happen. 
 

What I am surprised by and I’m sure that some of the more production or engineering members of the forum would be better placed to comment on, can you not hear a difference when bearings begin to fail? 

Maybe not. The mileage done by the helicopter was within the service range of the part that failed. It failed prematurely. Not an accident waiting to happen from that perspective. 

[An Away Move]

1 hour ago, chapero82 said:

So 4/5 survived the impact 😢 I was hoping they didn’t suffer 

Horrific. 

[EastAnglianFox]

I wish I hadn’t read it all now, but wow what a job the Pilot and Co pilot did in just 14 seconds in an attempt to not only give everybody the best chance of survival but also thinking of the built up area below..incredible.

 

But after reading that all I can think is, if it wasn’t for that raised concrete/kerb where they landed then there’s a chance it wouldn’t have toppled and less chance of a fuel leak and obviously a more easy escape route for any left conscious?

[Bellend Sebastian]

13 minutes ago, An Away Move said:

Maybe not. The mileage done by the helicopter was within the service range of the part that failed. It failed prematurely. Not an accident waiting to happen from that perspective. 

I'm as far from an expert as it's possible to be, but aren't accidents resulting from component failure within their service life really rare? The one thing I've learned from watching too many episodes of Air Crash Investigation is that a high proportion of accidents can be traced back to an individual messing up, be it pilot error, a botched repair, not sticking to the maintenance schedule etc etc.

 

Any incident like this is unfortunate, but this one seems incredibly unlucky

[StanSP]

18 minutes ago, EastAnglianFox said:

I wish I hadn’t read it all now, but wow what a job the Pilot and Co pilot did in just 14 seconds in an attempt to not only give everybody the best chance of survival but also thinking of the built up area below..incredible.

 

But after reading that all I can think is, if it wasn’t for that raised concrete/kerb where they landed then there’s a chance it wouldn’t have toppled and less chance of a fuel leak and obviously a more easy escape route for any left conscious?

The fuel leak could have occurred seconds before that, perhaps? 

 

Agree about pilot and Co-pilot. To have the speed of thought to soften the landing is incredible. In those seconds of chaos they still had the presence of mind to think of that. 

[Spudulike]

From the BBC... 

 

BBC News - Pilot could do 'very little' to stop Leicester City helicopter crash
https://www.bbc.co.uk/news/uk-england-leicestershire-66716572

 

[Super_horns]

Must have been so scary and and dreadful knowing what was going to happen and there wasn’t much that could be done to stop it .

RIP to those killed .

[fox_up_north]

Absolutely awful. Just can't comprehend it at all. No words.

[Trav Le Bleu]

3 hours ago, Sly said:

In essence, with the bearing failure in the rotor then, this was an accident waiting to happen. 
 

What I am surprised by and I’m sure that some of the more production or engineering members of the forum would be better placed to comment on, can you not hear a difference when bearings begin to fail? 

No engineer, but I would guess other engine noises and whooshing of blades might mask the sound of grinding bearings.

[Sly]

3 minutes ago, Trav Le Bleu said:

No engineer, but I would guess other engine noises and whooshing of blades might mask the sound of grinding bearings.

Yes, I’d debated that. 
 

I’ve just been discussing this with our Operations Manager where we work. He’s work on machinery for 25+ years in a noisy construction environment and he said that he can hear a difference in sound, when bearings start rubbing. However he is around it all day, so obviously knows the sound difference.  
 

I’m guessing pilots aren’t as attuned, as they’d normally be within the body of the helicopter. 
 

It’s so tragic and I’m guessing an in-depth investigation has been carried out by the bearings manufacturer. Something as daft as a change in the bearing housing itself could alter the entire dynamic.

 

Hopefully some of the recommendations that they’ve suggested are adopted. 

[jayfox26]

Still upsets me now reading about it. Absolutely heartbreaking 

[Hitesh]

14 minutes ago, Sly said:

Yes, I’d debated that. 
 

I’ve just been discussing this with our Operations Manager where we work. He’s work on machinery for 25+ years in a noisy construction environment and he said that he can hear a difference in sound, when bearings start rubbing. However he is around it all day, so obviously knows the sound difference.  
 

I’m guessing pilots aren’t as attuned, as they’d normally be within the body of the helicopter. 
 

It’s so tragic and I’m guessing an in-depth investigation has been carried out by the bearings manufacturer. Something as daft as a change in the bearing housing itself could alter the entire dynamic.

 

Hopefully some of the recommendations that they’ve suggested are adopted. 

Pilots would have also had headphones on which would have muffled any noise form the rear. 

A sad and tragic event and extremely unfortunate 

[Spudulike]

[FoxesWalk]

6 hours ago, Sly said:

In essence, with the bearing failure in the rotor then, this was an accident waiting to happen. 
 

What I am surprised by and I’m sure that some of the more production or engineering members of the forum would be better placed to comment on, can you not hear a difference when bearings begin to fail? 

Unlikely that in helicopter that you would hear anything obvious other than the rotors, maybe someone highly experienced as a technician would recognise a change, but I doubt a pilot would. I am speculating here, I have no direct practical experience of helicopters - only the analysis side. You’d likely have to remove and look at the bearing to observe any signs of fatigue.

 

The bearings will have been selected to the manufacturers stated loadcases and subject to rig and on-vehicle validation. Despite not specifically testing for rolling contact fatigue (a classic bearing failure mode) I expect the whole package was tested extensively. The bearings would have been analysed and rated for the stated loads. Particularly for aerospace applications I would expect the testing programmes to be exhaustive for the entire package. However, bearing lives are given as probabilities: the % chance of a part failing after X number of hours operating at a given load condition. Manufacturing variability and mounting errors could lead to significant outliers. There are lots of baked in assumptions, right back to what duty cycle you used when you selected the bearings in the first instance. In aerospace there are significant safety margins, and often failsafes (where possible and practical) due to the seriousness of mechanical failure. 

 

I’m not sure how routine servicing of this type of vehicle is scheduled or performed, but this is the type of inspection during which you may observe fatigue damage on a bearing. If the bearing did give up due to fatigue there would likely have been visible damage to the raceways in advance of the failure. Whether or not that component would be visible during a routine inspection, I don’t know. 

 

Source: I am a Mechanical Engineer with a PhD in rotating rotating machinery and have recently been working on the scheming and design for flying taxi transmissions (e-vtol), though most of my experience is on high end road cars and motorsport (transmissions). Whilst not a specific bearing expert I work with them a lot and have done failure investigations on bearings during my career. 
 

It really puts into context how important attention to detail is in mechanical engineering. In motorsport this type of failure in practice often means very little, but in aerospace applications, the consequences of mistakes are likely to be tragic. 
 

 

EDIT: I have just seen more detail of the report, which states “tail rotor duplex bearing likely experienced a combination of axial and bending moment loads which generated internal contact pressures sufficient to result in lubrication breakdown and the balls sliding along the race surface. This caused premature, surface initiated rolling contact fatigue damage to accumulate until the bearing seized”. Without seeing the layout drawings I cannot comment as to why these loads may be unexpected/higher than expected. They should be known loads. 
 

Further detail in the report suggests that there was not routine inspection of this bearing, and therefore it could not have been noted prematurely. A routine inspection of this component would likely have observed visible damage, in my opinion, based on the above description of the failure. I find it very surprising that they do not routinely inspect this component given it is safety critical. 

Sounds like there were also regulatory and testing failures here. 
 

Here are some examples of how pitting failure of a bearing raceway would progress, from SKF, a leading manufacturer. Based on the description above this type of damage would likely have been visible in advance of the catastrophic failure, but there was no inspection of the part based on that report: 

Note: this image is of a roller bearing, which has a line contact, but similar progression would occur for a ball bearing (like those in this helicopter), which has close to a point contact. 

Edited 6 September 2023 by FoxesWalk

[foxfanazer]

The darkest day in the clubs history. Still brings tears to my eyes now.

 

RIP to the best owner to ever exist and to the 4 other victims