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Old 5th Oct 2015, 16:28   #121 (permalink)
 
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S-76

SAS, RVDT and lynnx,

This is conjecture based on the quite limited information in the posted accident report, and assuming that the input rod linkage to the forward main servo has become disconnected.

If there was no pilot or AFCS input to the controls at the moment of separation, the servo would stay in place and from that point that attachment point on the swashplate becomes a fixed point, a fulcrum if you will. Some of the comments referred to the servo fully extending. That might be possible if there was an input at the moment of separation. However, if the forward servo had gone hardover ( remember, a disconnected control input means that the follow-up link would not stop the servo from moving at an intermediate point ), then the initial described aircraft reaction would have been much more violent than has been posted.

Back to the fulcrum point. With the attachment from the forward servo to the swashplate fixed in space, , then other control inputs would be affected. A collective input would then tilt the swashplate, instead of moving it up or down at whatever tilt it had. The head moment that is the moment placed on the vehicle thru tilting the control axis, is quite strong on the 76 ( some have seen the videos of the armed 76 doing rolls etc ), so the resultant unexpected cross coupling would certainly baffle the crew.

At this point, it is hard to say much more, except that the FDR analysis ought to shed more light on this aspect of the crash, and translate pure conjecture into fact. Focus has to be on the disconnect, maintenance history etc.

John
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Old 5th Oct 2015, 16:33   #122 (permalink)
 
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S-76

SAS, RVDT and lynnx,

This is conjecture based on the quite limited information in the posted accident report, and assuming that the input rod linkage to the forward main servo has become disconnected.

If there was no pilot or AFCS input to the controls at the moment of separation, the servo would stay in place and from that point that attachment point on the swashplate becomes a fixed point, a fulcrum if you will. Some of the comments referred to the servo fully extending. That might be possible if there was an input at the moment of separation. However, if the forward servo had gone hardover ( full extension ) , then the initial described aircraft reaction would have been much more violent than has been posted.

Back to the fulcrum point. With the attachment from the forward servo to the swashplate fixed in space, , then other control inputs would be affected. A collective input would then tilt the swashplate, instead of moving it up or down at whatever tilt it had. The head moment that is the moment placed on the vehicle thru tilting the control axis, is quite strong on the 76 ( some have seen the videos of the armed 76 doing rolls etc ), so the resultant unexpected cross coupling would certainly baffle the crew.

At this point, it is hard to say much more, except that the FDR analysis ought to shed more light on this aspect of the crash, and translate pure conjecture into fact. Focus has to be on the disconnect, maintenance history etc.

John
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Old 5th Oct 2015, 17:49   #123 (permalink)
 
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I believe that if the rod was totally disconnected at the lower end then the weight of the rod still attached at the upper end to the servo input under the influence of gravity would try to drive the servo to max travel. This would continue unless the rod jammed against the structure in which case the servo would stop in a random position.
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Old 5th Oct 2015, 18:24   #124 (permalink)
 
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Servo Movement

Point is valid Eric, but there is another factor, or should I mention two factors in play. The breakout force required to move the pilot valve, and the stiction of the system left after rod disconnect. If high enough, the valve could remain centered.

All this should come out in the detailed investigation, and you may be correct. As I wrote, though, if a servo went hardover ( and BTW, my recollection is anything but 100% accurate ) the servo's are typically designed for 100%/second rate, and if the servo went to full extension at that rate, the resulting initial maneuver would have been different than reported.

John
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Old 5th Oct 2015, 18:56   #125 (permalink)
 
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Well, they say what goes around, comes around - and I,ve just had the wavy finger pointed firmly in my direction lol.
I still think that the weight of the (separated) rod attached to the input would run the the servo down (not up) but I like and appreciate the fixed fulcrum theory and the resultant confusion.
I,m leaving it to the big boys now!
Lynnx out.
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Old 5th Oct 2015, 21:50   #126 (permalink)
 
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Hi Lynnx

I have never heard of a servo down in a crash report they always go hard over when separated from the input.
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Old 20th Oct 2015, 21:33   #127 (permalink)
 
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It seems strange why the CVR and FDR data not yet published. All the speculations will be exhausted if this data will come public.

If the FDR data will be converted to be an animation and this animation is accompanied by the CVR audio recording, so the overall situation provides a clear picture of what really has happened.

CVR and FDR are installed in the helicopter just in the cause of the accident can be quickly and reliably verified.


What’s wrong?
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Old 21st Oct 2015, 12:15   #128 (permalink)
 
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Quote:
Originally Posted by Copterline 103 View Post
It seems strange why the CVR and FDR data not yet published.
FDR data and relevant CVR data should be published as part of the accident report. They should not be published in haste just so that armchair "investigators", pilots, passengers and the press can have their wild speculations and gossip down the pub, fed.
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Old 23rd Oct 2015, 16:07   #129 (permalink)
 
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well my friend you never saw me cause I always looked n the roof and in the
couls may be that is why I am still here after 35 years n the air and 11 years of retirement god bell britow helis
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Old 27th Mar 2016, 21:38   #130 (permalink)
 
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Quote:
ASN Wiki Base Occurrence # 178588
Date: 12-AUG-2015
Time: 15:31 LT
Type: Sikorsky S-76C+
Owner/operator: Bristow Helicopters (Nigeria)
Registration: 5N-BGD C/n / msn: 76-0540
Fatalities: Fatalities: 6 / Occupants: 12
Airplane damage: Written off (damaged beyond repair)
Location: off Oworonshoki, Lagos Lagoon - Nigeria

Phase: En route
Nature: Non Scheduled Passenger
Departure airport: 'SEDCO' Offshore Drilling Rig
Destination airport: Lagos-Murtala Muhammed International Airport (LOS/DNMM)
Narrative:
A Sikorsky S-76C+, a domestic chartered flight operated by Bristow Helicopters Ltd (Nigeria), crashed into the Lagoon at Oworonshoki
area of Lagos. Visual meteorological conditions prevailed at the time and a VFR flight plan was filed. The two flight crewmembers and four of the ten passengers were fatally injured. The helicopter was destroyed and there was no fire.

Preliminary flight recorder data indicated that at 1000ft and 120Kts, the helicopter experienced sudden pitch up, and left roll with varying attitude of yaw, roll and pitch for 12 seconds until it impacted water at about 1531hrs.
Do someone knows where this FDR data is available?

Quote:
1. Visual meteorological conditions prevailed
2. flight recorder data indicated that at 1000ft and 120Kts
3. sudden pitch up
4. left roll with varying attitude of yaw
5. roll and pitch for 12 seconds until it impacted water
6. the two flight crewmembers and four of the ten passengers were fatally injured
+ unofficial information that the hydraulic fluid was contaminated.
Okey, Houston, we've had a problem here!

Last edited by Copterline 103; 27th Mar 2016 at 21:40. Reason: Typo corrections
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Old 19th Jul 2016, 14:24   #131 (permalink)
 
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Final Accident Report

Three weeks to go and then we are able to see what was the case. The Final Accident Report should be published within 12 months? The report will explain e.g.!why S76C+ came suddenly unflyable and was the Hydraulic Fluid contaminated or not?
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Old 1st Jan 2017, 09:40   #132 (permalink)
 
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Final Accident Report

Quote:
Originally Posted by Copterline 103 View Post
Three weeks to go and then we are able to see what was the case. The Final Accident Report should be published within 12 months? The report will explain e.g.!why S76C+ came suddenly unflyable and was the Hydraulic Fluid contaminated or not?
The 60 days stakeholders comment period is past already (12.10.2016). This delay is supporting my theory and knowledge of the most probable cause of this accident. The reality is that the stakeholder (captain Jay's family) can't and don't have the power needed to postpone publishing of the final accident report (the truth).

In the Baltic Sea Accident one of the stakeholder was able to kept the Final Accident Report on hold position more than year until the needed changes was done (to delete some of the factual findings before publishing the report).

This Final Accident Report should be published without unnecessary delays to confirm that S76 series helicopters are safe. This information is necessary to be published to secure the safety of all crews and people who are operating S76 series helicopters. This relevant safety issue should also be carefully evaluated and to be mitigated of the president-elected, Mr. Trump's and his family's flights with three S76B helicopters what the president-elected owns.

I hope that this safety issue has already been carefully taken account by the people who are responsible of president-elected's and his family's safety.
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Old 21st Jun 2017, 21:35   #133 (permalink)
 
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Sikorsky S76C+ PK-FUP Indonesia 21.3.2015

PK-FUP.png
"There was no indications of a malfunction in the aircraft systems before the aircraft loss of control occurred".


This is a Sikorsky S76C+ accident in Indonesia 21.3.2015. Most likely we will see similar flight data from Nigeria AIB's final accident report when, if ever will be officially published. Interesting to see if the hydraulic fluid will be contaminated due to sudden wear of Nylon-Teflon servo actuator piston ring?


Let's hope that everything is good and the helo type is safe to fly now and in the future.
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Old 15th Jul 2017, 16:11   #134 (permalink)
 
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News from Nigeria regarding this report.

AIB set to release Bristow Helicopter crash report, others - Vanguard News
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