Bristow S76 down in Lagos discussion (Not condolences)
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
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
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
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
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.
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
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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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.
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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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?
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?
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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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
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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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.
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.
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.
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.
Last edited by Copterline 103; 27th Mar 2016 at 21:40. Reason: Typo corrections
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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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Final Accident Report
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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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.
"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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Copterline 103 FDR data after fwd servo failure
This is the Sikorsky 76C+ OH-HCR (Copterline 103) FDR data after fwd servo uncommand extension due to the blockage of Servo Actuator C3 return ports.
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S76 C+ s/n 466 Harrods Aviation LTD Servo Pistons
These pictures of s/n 466 are almost identical with s/n 508 (Copterline 103). The defect of s/n 466 Servo Actuator pistons may be an airsafety issue?
From what I understand, if the after start hydraulic servo checks had been done properly in the Copterline example then that aircraft should have been grounded. The importance of doing this check as per the RFM can't be over emphasized. I see so many S76 pilots do this check incorrectly during their annual recurrent sim training.
The Indonesia accident mentioned earlier had nothing to do with hydraulic servos.
The Indonesia accident mentioned earlier had nothing to do with hydraulic servos.
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COPTERLINE 103
gulliBell:
Your theory is naive. Helicopter servos doesn’t move much while the helicopter is in the ground or the helicopter is taxing. When the autopilot is engaged the Electric Line Actuators are giving some slight control commands to the servos. When the helicopter is lifted to the hover and during the flying phase 99.99 percent of the servo's movements, loads and stress will be actualized to the Servo Actuators. In the practice the work load, aerodynamical load, vibrations to the Servo Actuators will be generated during flight phase only.
Your theory doesn’t take into account that the most likely the plasma flakes or plasma particles are chipping (remove)from the head of the Servo Actuator’s Piston during flight phase and blocks the C3 return port or C3 ports during the flight phase.
It is very unlikely that the plasma will be removing from the piston head at time when the helicopter is in the ground run or taxing. In the ground the servo actuators don’t have any moves, loads, aerodynamical loads or vibration. This all loads are mostly generated by the M/R Blades as a function of airspeed / vibration. The Servo Actuators will take on all the aerodynamic loads that the main rotor generates during the main rotor generates the lift. This aerodynamic load is very huge especially for the forward Servo Actuator. The other Servo Actuators are having much less aerodynamic load than the forward Servo Actuator.
It is possible but improbably that the Servo Actuator’s piston plasma coating chipping will happen in the ground when the Servo Actuators are almost “frozen” phase.
The helicopter will be safe if this plasma chipping or plasma flakes separation from the Piston will happen in the ground phase. The common sense is saying that the risk for chipping or plasma separation from the Piston head and that the plasma flakes will obstruct Servo Actuator’s C3 return fluid ports. The partial blockage is enough to cause the Actuator Piston Jam. When the Piston is jammed, the Servo out put will not respond to control inputs. This will lead to the Loss of the affected channel. The loss of Servo Channel will possible cause the loss of the control of entire aircraft. The consequence may most likely to be a fatal.
The S76 system design is not capable to identify Actuator Piston Jam by SER.JAM CAUTION because in case the “jam” has been caused by the blockage of the C3 return port(s). The MCV is still capable to move but the return port(s) are block. The Servo Actuator is “jammed” but with out any caution to the helicopter caution and warning system. The SER.JAM CAUTION is activated if the MCV is mechanically jammed. The flight crew don’t have any indication that the Servo Actuator has failed. When the one of the tree Servo Actuators are frozen, fully extended or not working parallel with the other the Mixing Unit will finally to mix helicopter steering logic. This will lead to the situation where the helicopter is unflyable. The problem is very well investigated and analyzed already by the end of 70’s e.g. by H-53 helicopters accident investigations.
Looking forward to see Bristow Helicopter’s accident 12th of August, 2015 accident report why the S76C+ was spiraling and acting precisely like COPTERLINE 103 and what was the reason for the second accident when Bristow Helicopter S76 become unflyable 3rd of February, 2015.
Last edited by Copterline 103; 15th Feb 2018 at 22:59. Reason: Attachment