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AW139 incident - Houma

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AW139 incident - Houma

Old 9th Oct 2022, 04:18
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Originally Posted by SASless View Post
So which came. first....the Chicken or the Egg?

The Crew reported a very serious electrical fire AND a loss of Collective Control AND Dual High Side failures which did not respond to the ECL's and had to be controlled by switching back and forth between Flight and Idle....... am I understanding that is what they reported correctly?

For Coyote,,,,,had they confused the BAT MAIN and BAT MASTER switches.....what would be the result if they somehow switched BAT MASTER to OFF rather than BAT MAIN OFF?

Likewise....what if they had gotten it right and did as the procedure calls for....and turned BAT MAIN to OFF....what would have happened (re instrumentation and controls?
With no generators online at this stage of the electrical fire/smoke checklist, switching BATTERY MASTER off instead of BATTERY MAIN will result in a complete lost of electrical power and cockpit will go black. Bad Juju if you are IMC. The engines however produce power via the PMA which should keep the EEC's running in AUTO.

Switching BATTERY MAIN off as per the checklist, will result in the loss of all but the DC ESSENTIAL busses. Copilot screens, both MCDU's, MAU1 and AP1 lost amongst a host of other stuff. Pilot screens, ESIS and AP2 with ATT remain to keep it flyable IMC.
Flight controls, aside from auto flight and SAS, should be otherwise unaffected by electrical power loss. If they had loss of collective control, it must have been mechanical failure in my view, and I don't think they would have survived.
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Old 9th Oct 2022, 12:12
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Originally Posted by the coyote View Post
With no generators online at this stage of the electrical fire/smoke checklist, switching BATTERY MASTER off instead of BATTERY MAIN will result in a complete lost of electrical power and cockpit will go black. Bad Juju if you are IMC. The engines however produce power via the PMA which should keep the EEC's running in AUTO.

Switching BATTERY MAIN off as per the checklist, will result in the loss of all but the DC ESSENTIAL busses. Copilot screens, both MCDU's, MAU1 and AP1 lost amongst a host of other stuff. Pilot screens, ESIS and AP2 with ATT remain to keep it flyable IMC.
Flight controls, aside from auto flight and SAS, should be otherwise unaffected by electrical power loss. If they had loss of collective control, it must have been mechanical failure in my view, and I don't think they would have survived.
hi,
you exactly right on all your comments except the last one, military pilots train themselves to recover a stuck collective, and it is exactly what has done that guy. He has done really good, bringing down the machine to the ground progressively in several circles, just withe collective and the engine power control through the mode switches!
cheers
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Old 9th Oct 2022, 13:05
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Event occurred on 24 September.....a full two weeks ago.


To date there has been no emergency AD's or related Safety Messages resulting from the Investigation.

That despite the aircraft being intact, the Crew unhurt, and sufficient time to determine what caused the loss of Collective Control if there was a mechanical failure in the Flight Control Linkage.

Is the absence of comment about that significant at this point in time?

Additionally, it would seem two weeks would have been ample time to ascertain the location of the electrical fire....yet again no information being made public yet.

The Investigation will take some time and a Report will be made public....but the absence of Emergency AD's seems a bit odd.
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Old 10th Oct 2022, 00:23
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Originally Posted by JGtn View Post
hi,
you exactly right on all your comments except the last one, military pilots train themselves to recover a stuck collective, and it is exactly what has done that guy. He has done really good, bringing down the machine to the ground progressively in several circles, just withe collective and the engine power control through the mode switches!
cheers
We all train for a stuck collective and jammed controls, civil or military. The video shows straight and level flight prior to landing, which to me means there is a fair bit of collective pitch "stuck" there. The report states they killed the engines at 200 feet. I'd be interested to hear how you think a safe landing is possible with that amount of collective pitch from 200 feet if all engine power is removed?
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Old 12th Oct 2022, 04:18
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Originally Posted by SASless View Post
Event occurred on 24 September.....a full two weeks ago.


To date there has been no emergency AD's or related Safety Messages resulting from the Investigation.

That despite the aircraft being intact, the Crew unhurt, and sufficient time to determine what caused the loss of Collective Control if there was a mechanical failure in the Flight Control Linkage.

Is the absence of comment about that significant at this point in time?

Additionally, it would seem two weeks would have been ample time to ascertain the location of the electrical fire....yet again no information being made public yet.

The Investigation will take some time and a Report will be made public....but the absence of Emergency AD's seems a bit odd.
The EASB has just been issued.

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Old 12th Oct 2022, 16:53
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Anyone have a link to the full “Emergency Alert”?
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Old 12th Oct 2022, 19:48
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Originally Posted by albatross View Post
Anyone have a link to the full “Emergency Alert”?
AW139/AB139 ASB EASA 2022-0209-E
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Old 13th Oct 2022, 06:18
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Originally Posted by the coyote View Post
The electrical fire/smoke checklist calls for switching GEN1 and GEN2 off and then BATTERY MAIN off. If you mistakenly switch off BATTERY MASTER instead of BATTERY MAIN at this point (and they are right next to each other) you will lose all electrical power and instruments.
This reminds me of the "Which button gets me a latte?" movie scene (Monsters vs Aliens). Precarious....
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Old 20th Oct 2022, 11:57
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NTSB Preliminary report: https://data.ntsb.gov/carol-repgen/a...ort/105994/pdf
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Old 20th Oct 2022, 12:25
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Still worthy of a Green Endorsement (Brit Mil thing) for getting it safely on the ground with no injuries but I don't understand why they didn't manually move the ECLs when they realised the beep trims weren't working.

That is a complex emergency that most (including me) would struggle to sort out.

No doubt all the 139 sim instructors out there are working out how to replicate it.......

If that C3 torque tube had burnt through or completely deformed it would have been a much more serious outcome.
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Old 20th Oct 2022, 13:06
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Originally Posted by [email protected] View Post
Still worthy of a Green Endorsement (Brit Mil thing) for getting it safely on the ground with no injuries but I don't understand why they didn't manually move the ECLs when they realised the beep trims weren't working.

That is a complex emergency that most (including me) would struggle to sort out.

No doubt all the 139 sim instructors out there are working out how to replicate it.......

If that C3 torque tube had burnt through or completely deformed it would have been a much more serious outcome.
Probably an AFC! They just handed one out to the C17 pilot that jumped over the bus that entered the runway at Kabul last year.

The manual ECL question will be interesting to understand and will hopefully be answered in due course.

This incident also illustrates how luck can be a major element in the success or otherwise of such a failure - at night over the ogin I think the outcome would have been different.
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Old 20th Oct 2022, 13:12
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but I don't understand why they didn't manually move the ECLs when they realised the beep trims weren't working.
True, but easy to say from the comfort of an armchair as opposed to a burning cockpit.
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Old 20th Oct 2022, 13:42
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Reading the Report it appears to me that the affected control tube is not metallic....am I right in that?

If so...had it been of metallic construction would that Tube have been damaged as it was?



Also I feel I was asking the right question when early on I posed this question.....


Originally Posted by SASless View Post
One of the media reports said the Pilots could move the Collective Lever in full range of motion....from down stop to top stop...without any reaction from the Rotor System.

If that is true....then there must have been something that happened to sever the mechanical linkage for the Collective.....arcing from a chafed wired bundle.....fire?


The Control Tube was not severed but was compromised to the extent that the flight controls were damaged badly enough to greatly compromise their effectiveness.

Two very rare and apparently unrelated problems happening at the same time is more than mere coincidence.

The good news is now we have a full understanding of what caused the problems and the relevant questions may begin to be answered as to how to prevent a recurrence can begin.

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Old 20th Oct 2022, 14:00
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Preliminary report released

https://data.ntsb.gov/carol-repgen/a...ort/105994/pdf
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Old 20th Oct 2022, 14:01
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See post 89......
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Old 20th Oct 2022, 15:16
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Originally Posted by SASless View Post
Reading the Report it appears to me that the affected control tube is not metallic....am I right in that?
In the pics it looks like CFRP material

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Old 20th Oct 2022, 15:37
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Maybe they didn't remember the ECL levers are there, LOL. We were did a flight test program with Era and the pilots said they never touch the levers, they just leave them in FLIGHT.
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Old 20th Oct 2022, 16:01
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That sounds like a training ad standards deficiency if true.

Editted to add clarity......my response was re "retools" noting what he had been told by ERA Pilots during the flight test program.....and is not directed towards the Crew that encountered the inflight problems.

Training and Sim Courses cannot replicate or identify every possible malfunction or emergency that might be encountered but I would think ECL's might have a role to play in certain situations and when I saw the word. "never"....it made me wonder why the Pilots at said that.


Last edited by SASless; 21st Oct 2022 at 00:14.
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Old 20th Oct 2022, 19:50
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Originally Posted by SASless View Post
Reading the Report it appears to me that the affected control tube is not metallic....am I right in that?

If so...had it been of metallic construction would that Tube have been damaged as it was?



Also I feel I was asking the right question when early on I posed this question.....






The Control Tube was not severed but was compromised to the extent that the flight controls were damaged badly enough to greatly compromise their effectiveness.

Two very rare and apparently unrelated problems happening at the same time is more than mere coincidence.

The good news is now we have a full understanding of what caused the problems and the relevant questions may begin to be answered as to how to prevent a recurrence can begin.
The joys of CFRP in modern aircraft and unintended consequences! Most people understand CFRP as just "fancy fibreglass" and a composite material but forget or do not realise that Carbon Fibre conducts electricity quite well. When you get a large current flowing through it the filaments get hot, unlike a metal component that might melt locally at the contact point and break the short circuit. Whether it would have made a difference here is questionable.

The cable in question would have got the full output of GEN 1 by the looks i.e. 300 Amps or better. Certainly would have been a significant "whoof"!

The more "electric" aircraft get means a lot more respect to electrical components needs to be paid as the consequences can go a lot further than expected. Seems the issue was QC at manufacture?

Know of a machine that had aftermarket combined nav light / strobes fitted. Short between high voltage strobe wire and nav light wiring blew out both collective LVDT's and FADECs reset to a nominal Nr which was substantially lower than normal. Turned out that in one of the overhead panel connectors the nearest pin to the NAV wiring was part of the FADEC circuit!

There are also issues with bonding of CFRP with regard to lightning strike. You need a low resistance path to dissipate the energy and not cause high resistance and subsequent heating which can possibly cause the structure to fail. Hence CFRP structures normally have a copper mesh embedded in the surface of the structure. Being electrically conductive also brings up the issue of galvanic corrosion and dissimilar materials. I have seen some ugly stuff where CFRP, its copper mesh are other alloy structures need to be bonded. Al alloy and copper? WTF?
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Old 20th Oct 2022, 20:33
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I wonder if the wiring bundle was incorrectly secured during assembly or after delivery from the factory.
It will be a “learning experience” for a Quality Assurance and Inspection Team somewhere.
Perhaps the Torque Tube needs to be changed to a less vulnerable material.
Obiously there were multiple holes in the Swiss Cheese slices in this incident.
It must have been very interesting for the crew concerned.
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