Bristow emergency landing
 

There doesn't seem to be a date on that story. Can anyone paste in the full story?

Don't have the full story, but digging a bit deeper gives this as date:

AIBN News bulletin
 

The essence of a brief statement last night from the NSIA (previously AIBN) is something like this:

On Friday the 25. of September the crew of a S-92A, LN-ONQ on a return flight to Sola from West Elara, got warning that the oil pressure in the MGB had dropped. Later , as the oil temperature started rising, the crew transmitted a MAYDAY call and continued the descent to 200'. They prepared for a ditching if the pressure drop should continue that far. The landing at Sola was uneventful and they were escorted to parking by the emergency services.

The AIBN arrived the same evening and started their investigation. No causes for the event has so far been establised.

Anyone have any more info?

Presume they didnt goto MAN COOL so makes sense the temp increased.

92
 

https://verticalmag.com/news/norwegi...tion-incident/

Amazingly lucky. Once again reminding that S92A gearbox is a deathtrap...it cannot actually run dry. Recall their Part 29 certification run-dry "extremely remote" clause basis was on the oil leak occurring in the cooler circuit, and the mitigation was to bypass the cooler loop.

If you lose oil from the MGB itself for any other reason (i.e. filter mount like Cougar, or literally any other main case penetration) then you're hosed.

8 minutes.

Seems odd that just losing 4 litres out of the normal 30 litres should cause such a nasty problem?

I suspect the oil leak was a consequence rather than the cause.

Mechanical problem in the input module, leading to lots of heat being generated, leading to oil seals between modules being compromised, as well as heating up the MGB oil.

Only speculation on my part.

That makes sense Apate but raises the question of the design of the input module.

Death trap? What rubbish. Turned out alright didnt it. They had a caution, not a warning, the OIL OUT is land immediately, they obviously didnt have that and they had sufficient pressure to continue flight to land.

Simply because this particular incident didn't lead to an actual full oil-out condition since they were already on approach (it would only have been a matter of time with the leak as described) doesn't change the issue that the S92A MGB cannot operate without oil for more than approximately 8 minutes.

The fact that it holds Part 29 certification despite this is mind boggling, particularity since there have been enough incidents of leaks from the MGB case to make the "extremely remote" 10^−7 occurrence clause statistical nonsense.

Weren't they on their way back? So it could have been losing oil for the previous 2 hours or so... it was hardly a catastrophic event.

The gearbox has a good record.

over a million hours in the sky, not bad for a deathtrap.

What planet do you live on?

I'm sure that's comforting to the families of the 17 victims of Cougar 91, or the luckier CHC crew the year before.

But its still an order of magnitude below the number of hours required (10^7) without a single loss of MGB case lube incident to verify its certification loophole basis.

If the gearbox is so good, how come a loss of between 10 and 15% of the oil led to such massive overheating of the input module? 214 degrees C!

The cougar crew unfortunately didnt help that situation and a false understanding led them to continue flying.

Because a drop in pressure triggers the cooler bypass... they could have chosen to reverse the bypass and cool the oil, they obviously knew where the issue was and it wasnt the cooler.

so if the problem isn't the cooler, why not reverse the bypass? If the leak is in the no 1 input module its going to keep leaking regardless isn't it? Why risk overheating the engine inputs as well?

Not a 92 driver so just keen to understand.

I think the purpose of the bypass is to save as much oil as possible in the event of a leak. Hot oil is better than no oil. I can’t remember what the capacity of the cooler is, I’m on leave but it takes a fair amount.

Probably because the checklist doesn't say to...

We don't actually know their exact indications, what the pressure was and what visual signs they had. Whatever it was, they got everyone home safe, a good day all around.

:ok: Agreed - MRGB problems over the water are not nice.

They didn’t know where the problem originated from. They had indications of reduced pressure and increasing oil temp. They discussed but opted not to Man Cool as they couldn’t be sure the cooler wasn’t leaking.

LZ

Norwegian S-92 suffers oil leak in ‘serious aviation incident’

Estimated reading time 3 minutes, 22 seconds.

Norwegian authorities are investigating what they describe as a “serious aviation incident,” after a Sikorsky S-92A suffered an oil leak that forced the crew to declare mayday before landing safely.

The incident took place on Sept. 25, 2020, as the Bristow Norway-operated aircraft returned to Sola from the West Elara oil installation. About 25 to 30 nautical miles southwest of Sola, as the aircraft was making a descent from 7,000 feet to 1,000 feet, its crew received a caution that the oil pressure on the main gearbox had dropped below 45 psi.

Shortly afterwards, the caution “INPUT/AA #1 HOT” came on, and the crew followed the emergency checklist to put the left engine back to idle.

The oil pressure continued to drop to below 35 psi, and the oil cooler automatically switched off. As the aircraft continued its approach to Sola, the oil temperature rose and the caution “INPUT/ACC #2 HOT” came on. The oil reached a peak temperature of 214 C.

The crew declared mayday as they continued to descend to 200 feet, and were preparing to ditch in the sea if the oil pressure disappeared completely.

However, the aircraft was able to land normally at Sola, and it was followed to a standstill by the airport’s fire and rescue department.

The Norwegian Safety Investigation Authority arrived that evening to begin their investigation into the incident, and found about four liters of oil missing from the main gearbox. The main gearbox normally contains about 30 liters of oil.

Investigators found some oil spill on the left engine and left side of the main gearbox, and there was oil on the outside of the helicopter, particularly on the left side of the fuselage.

They noted that the oil appeared to come from the left engine input to the main gearbox area, but there were no signs of leakage in the oil cooler or its hose connections.

An indicator that warns of a high pressure difference across the oil filter had come out, but the investigators saw no particles during an initial visual inspection of the oil filter, and they found no metal particles on the main gearbox’s magnetic plugs.

The main gearbox has been removed and is to be sent to Sikorsky for further analysis.

The NSIA said it will continue its investigation with help from the U.S. National Transportation Safety Board.

Anybody knowledgable with the 92 care to point out how it currently complies with the CS criteria?

1/ Apparently doesn't meet the "run dry" capability as has been proven in the field and by FAA testing.

2/ Starting to prove that it doesn't meet the remaining criteria for improbability?

Apples to apples you may be better off in a 225!

Err, no thanks. :mad:

Really? Using the trite analysis that most people use for analysis the 225 is still safer by a factor of about 3-4?

You know what trite rhymes with, about sums it up....

My thoughts entirely - they both probably rhyme with trite and are as bad as each other.

Don't have to get in either of them and would not anyway, just surprised at the way people perceive things.

We must not forget the basic definition of the helicopter:

”Thousand of parts rotating around an oil leak waiting for metal fatigue to set in”

Statistics...........inevitability!

Genuine question, if the aircraft landed safely, why is the NSIA looking at this? Is it because it is a HiPo event? I'm not surprised they are taking a keen interest but having a team on site etc seems like they want to be in charge. What did I miss?

There was no disastrous outcome. They landed at SOLA.

Yes, a good result in that respect but the MRGB is being removed and sent to Sikorsky - engineering-wise that is a disastrous and expensive outcome from just the loss of 12% of its oil.

I don't want to shout, but the event would NOT have been caused by the loss of 12% of the oil. The oil loss will be a consequence.

My money is on either a mechanical issue in the #1 input module, or a failure of the oil scavange from the #1 input module which then led to "churning". It was overheating of the input module and then partial failure of mating seals between the input module and main module that resulted in some loss of oil.

Of course, I could be wrong ;)

They might want to understand how close to real disaster this was.
Even a ditching (notwithstanding a fatal crash) in cozy Norwegian Winter North Sea conditions is something they would dearly like to avoid, I guess.

I'm struggling to remember where and when but hasnt this churning issue happened before and had a very similar situation.

From AIN online 2011 so an input module problem can cause a loss of oil and oil pressure so that the engine has to be brought to idle, the bypass to the cooler automatically operates leading to both engine input modules overheating??

Wouldn't be fun further out to sea IMC!

How much longer would it have taken to drop the oil pressure enough for them to ditch?

Surely a system with lots of redundancy would allow continued ops on one engine without problems?

Please shout all you like but I struggle to see how this is a well designed MRGB.

It was Brunei in 2008 (11:26 on18th Jan to be precise!) The symptoms were a lot more dramatic and rapid though, but possibly because in this event the engine was brought to idle. That was one of several changes that came in as a result (including Adding the INPUT HOT caution).

From reading the news report the engine was idled due to INPUT ACC HOT #1 caution but that would have been caused by the MGB Oil Cooler being auto bypassed due to loss of oil pressure in the MGB.

afaik
The MGB oil cooler is separate from the MGB so it is a possible oil leak location and that is why it will be automatically bypassed (pressure drop). If the oil pressure drop continues then the bypass can be cancelled as a possible leak is not in the cooler.

I dont think you would need to idle an engine as you would expect 'input acc hot #n' once MGB bypass is activated, you have the APU to fire up to provide electric power if need be if you lose a generator in the accessory, which btw shares oil with the MGB.

Without the proper report coming out we will have to wait and see what actually has occurred (as actually as they can get).

Getting an INPUT ACC HOT by itself would not cause the oil cooler to auto bypass.

There must have been a reduction in pressure to cause the bypass, basically an amber MGB OIL PRESS caption.