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Uncontrolled yaw on Agusta 119 air ambulance in South Africa.

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Uncontrolled yaw on Agusta 119 air ambulance in South Africa.

Old 13th May 2022, 13:35
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Uncontrolled yaw on Agusta 119 air ambulance in South Africa.

Preliminary South African report is here,

http://www.caa.co.za/Latest%20Accide...-%20ZT-RZS.pdf

text below if from the news report of the incident

Two paramedics aboard a helicopter careering in circles on a hospital roof didn't hang around and hope for the best.

The pair hurled themselves out of the Agusta onto Paarl Hospital's helipad — one injuring himself in the process — while the pilot battled to control the pirouetting helicopter.

Once the pilot shut down the engine, he also leapt out of the aircraft while the rotor blades were still spinning.

Details of the drama, which unfolded on the 30m roof at 1am on February 19, emerged this week in a preliminary serious incident report issued by the SA Civil Aviation Authority (CAA).

The report says a battery of tests have been conducted on the seven-year-old single-engine aircraft but does not indicate any progress in finding out what caused its problems.

The 37-year-old pilot and paramedics aboard the helicopter were preparing to fly to Cape Town International Airport when the incident happened, says the CAA report.

When the main rotor approached the speed required for take-off “the helicopter abruptly experienced a violent yaw to the left side of approximately 90°; it then stopped for about a second”.

The pilot attempted to control the aircraft with the right rudder pedal but “a second violent yaw to the left side ensued in two full rotations (of 360º) before the helicopter stopped again for approximately two seconds”.

The report added: “Thereafter, a third rotation to the left side ensued; at this point (when the third rotation started), the two paramedics decided to disembark the helicopter voluntarily without alerting the pilot about their intention.

“Meanwhile, as the helicopter advanced through the third 360º yaw to the left side, the pilot rolled the throttle closed. This action slowly stopped the yaw rate.

“The pilot then managed to get the helicopter to ground idle. He then shut down the engine and switched off all power. He then disembarked the helicopter while the rotor blades were still in motion just in case the helicopter started to yaw uncontrollably again.

“One of the paramedics sustained minor injuries after being dragged by the helicopter skids while disembarking the helicopter; the pilot and the second paramedic were not injured. There were no visible damages to the helicopter.”

According to the CAA report, the AW119 Koala single-turbine helicopter can carry seven passengers plus the pilot, or slung loads up to 1,000kg.

Its maximum fully loaded range is more than 650km and it is primarily used for search and rescue, medical evacuation, surveillance, and passenger and light cargo transport.

https://www.sowetanlive.co.za/news/s...l-roof-report/
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Old 13th May 2022, 17:31
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Does the 119 share any components in the TR drive train with the 429? particularly TR servos.

I only ask because a friend had uncontrolled yaw on the ground in one and it took a long time for the fault to be acknowledged.
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Old 13th May 2022, 18:26
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Or with the 169? Asking for a other friend…
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Old 14th May 2022, 07:28
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Originally Posted by [email protected] View Post
Does the 119 share any components in the TR drive train with the 429? particularly TR servos.

I only ask because a friend had uncontrolled yaw on the ground in one and it took a long time for the fault to be acknowledged.
No the physical components aren't the same, but then it wasn't the tail rotor servos at fault on the Bell 429 (I make the assumption that by servo you mean the hydraulic servo). I don't think you're on the wrong track though (see later). For context the AW119 is essentially a single engine skidded variant of the A109E.

In the Bell 429 incidents it was the trim actuator building up a huge out of trim force through a "normal" AFCS mode. But that doesn't seem to it the situation here. The yaw rate happens as the aircraft is started so I assume the AFCS is not active at this point and therefore I think it's not the trim actuator. It's a left (power pedal) yaw so this indicates the tail rotor was functioning at very high power so a drive disconnect can be discounted. The pilot would be unlikely to have his feet away from the pedal and should naturally stomp down right pedal to stop a left yaw so the control run may be at fault.

However, back to your original point. I do think a hydraulic servo jam or runaway (there is a single servo in the yaw channel on AW119) could give the symptoms, which was what they originally thought had happened on the 429. I hope the investigation works it out
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Old 14th May 2022, 11:02
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It seems we are seeing these events in more than one Make and Model of helicopter....and as in the current event the symptoms seen dramatic and persistent rather than just one stroke and in one direction.

If it was an AFCS problem....Pilot input by use of the Tail Rotor Pedals should have overridden the AFCS Input and should have ended with the turning the AFCS to OFF.

Has the design of modern day AFCS systems given the AFCS the ability to match or exceed a Pilot Input using the Pedals?

Not having a Sperry Helipilot AFCS Manual at hand....memory tells me the AFCS only had something like a 20% authority and was easily overridden by flight control input.

If the installed AFCS system is similar to that....it would suggest it is not the AFCS in the current event in OZ. (at least in my thinking).

I would think it was hydraulic system related rather than AFCS.....again if my thinking is appropriate for the installed AFCS on the aircraft in OZ.

The description of the event shows a really "interesting" ride on that Roof Top Pad which lasted some period of time.
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Old 14th May 2022, 11:25
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Originally Posted by SASless View Post
It seems we are seeing these events in more than one Make and Model of helicopter....and as in the current event the symptoms seen dramatic and persistent rather than just one stroke and in one direction.

If it was an AFCS problem....Pilot input by use of the Tail Rotor Pedals should have overridden the AFCS Input and should have ended with the turning the AFCS to OFF.

Has the design of modern day AFCS systems given the AFCS the ability to match or exceed a Pilot Input using the Pedals?

Not having a Sperry Helipilot AFCS Manual at hand....memory tells me the AFCS only had something like a 20% authority and was easily overridden by flight control input.

If the installed AFCS system is similar to that....it would suggest it is not the AFCS in the current event in OZ. (at least in my thinking).

I would think it was hydraulic system related rather than AFCS.....again if my thinking is appropriate for the installed AFCS on the aircraft in OZ.

The description of the event shows a really "interesting" ride on that Roof Top Pad which lasted some period of time.
I do have the SHZ-109 manuals but unhelpfully they only say plus or minus 5mm of travel not percentage. In any case it's small. In the AW119 RFM it does show a trim actuator in yaw which would have full authority but is slow acting. However, in the Bell 429 case it wasn't a malfunction of the actuators "running away", it was more a mode of the AFCS commanding (incorrectly) full travel. In that case simply moving the pedals would not correct the problem - they had to be put in exactly the right place (the detent) or the trim release depressed. So here in the AW119 that could happen but I suspect not as in my experience of AW109 AFCS it is not active during start so wouldn't be commanding anything. My money on the servo.
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Old 14th May 2022, 12:18
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Thinking back to the Copterline S-76 Crash several years ago.....

The cause was determined to be a flight control actuator failure that caused loss of control of the aircraft.

"The Aircraft Accident Investigation Commission determined that the cause of the accident was an uncommanded extension of the main rotor forward actuator and subsequent loss of control of the helicopter. Contributing to the uncommanded extension of the actuator was the separation of the plasma coating on one of two actuator pistons and the operator’s failure to detect the internal leakage of the main rotor forward actuator.

In the months following the accident, the Commission initiated interim safety recommendations, which resulted in NTSB Safety Recommendations A-05-33 through -35, Sikorsky All Operators Letter CCS-76-AOL-05-2001, FAA Special Airworthiness Information Bulletin SW-06-15, and an FAA Notice of Proposed Role Making (2006-SW-05 AD).
From Rotorheads re the Copterline Accident.....

S76 down in Baltic Sea (Now incl NTSB Safety Recommendation)


Something unlikely as a plasma coating separating leaves all sorts of possible causes to be considered if the cause is thought to be a hydraulic servo.
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Old 14th May 2022, 16:53
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Thanks for the info Gipsymagpie
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Old 14th May 2022, 20:29
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I flew a 109 where on random occasions the cyclic would vibrate violently as soon as the battery was switched on. Turned out to be an internal failure of the SAS control box. In effect, the SAS was never disconnected.

I don’t know the 119, but I wonder if this was a similar issue.
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Old 15th May 2022, 08:10
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“The pilot then managed to get the helicopter to ground idle. He then shut down the engine and switched off all power. He then disembarked the helicopter while the rotor blades were still in motion just in case the helicopter started to yaw uncontrollably again.
Seems a bit counterintuitive to leave the controls and try to outrun an uncontrolled helicopter?
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Old 15th May 2022, 09:20
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When you have become a Passenger and the aircraft is doing the driving.....at some point it might make sense.

After all ....Fighter Pilots have ejection seats and parachutes.
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Old 15th May 2022, 17:13
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Wouldn’t, once recovered from shock and awe, immediately closing the throttle been the best course of action?
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Old 15th May 2022, 20:01
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Originally Posted by albatross View Post
Wouldn’t, once recovered from shock and awe, immediately closing the throttle been the best course of action?
That’s what the pilot did.
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Old 16th May 2022, 16:39
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Originally Posted by Hot and Hi View Post
That’s what the pilot did.
Yes, After the third uncontrolled rotation
The report is a little confusing as to throttle movements. First he reportedly closed the throttle then “managed to get the engine to ground idle” then he reportedly shut the engine shut down again. Hence my confusion.


From the report: “Meanwhile, as the helicopter advanced through the third 360º yaw to the left side, the pilot rolled the throttle closed. This action slowly stopped the yaw rate.

“The pilot then managed to get the helicopter to ground idle. He then shut down the engine and switched off all power. He then disembarked the helicopter while the rotor blades were still in motion just in case the helicopter started to yaw uncontrollably again.

Last edited by albatross; 16th May 2022 at 16:50.
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