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Bristow S76 Ditched in Nigeria today Feb 3 2016

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Bristow S76 Ditched in Nigeria today Feb 3 2016

Old 18th Mar 2016, 10:10
  #481 (permalink)  
 
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Originally Posted by industry insider
Here is the prelim report:

http://www.aib.gov.ng/files/pre-repo...tow-5N-BQJ.pdf

Yaw trim issue, fighting the DAFCS and maybe some uncoupling and PIO? Combined with a mental picture of August 12th?
So do you think the mentioned instrument problems were imaginary, or linked to some sort of electrical issue with the DAFCS? (I've no idea how the avionics works on a S76).

Anyway the fact they made a fully controlled ditching with no damage presumably means they were actually in full control even though they didn't think so.
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Old 18th Mar 2016, 18:15
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Yaw trim issue,fighting the DAFCS and maybe some uncoupling and PIO? Combined with a mentalpicture of August 12th?
So do you think the mentioned instrument problemswere imaginary, or linked to some sort of electrical issue with the DAFCS?


I have more than 4.500hours on type (S76C+) and more than 10.000 hours to study S76 flight control systems, S76 accidents where the loss of the controllability has been an issue. Also I have studied a lot of related accidents (H-53 and UH-60 the loss of controllability). In addition I have had a access to read more than 60.000 pages of non-public documents of this issue.

The investigators should have also an different approach. It looks that they are now following (preliminary report) the consequences, not the root cause.

The cause of TRIM and DAFSC caution could be also related to a jam or a partial jam of the helicopter flight control system. If the there are a jamming somewhere in flight control system (Servo Actuators, Control tubes and rods, Mixing Unit) it is possible that the Mixing Unit's mechanical compensations are really "mixing helicopter's steering" and the helicopter flight controls responses will come illogical. This could be the reason why the helicopter has come partial unflyable.

The perliminary report is stating:
1. TRM FAIL lights illuminated twice and were reset on the outboard leg
2. The EHSI and compass, the instrument readings inaccurate/inconsistent, the aircraft started a turn to the right with a high rate of decent
3. The PF called my attention to the collective being heavy and the power dropping anytime he pulled to maintain power
4. I noticed the controls not responding properly
5. I noticed the cyclic not responding to lateral movement
6. Relayed message "Okey they lost all their instruments"
7. Relayed message by two aircrafts "the aircraft was not responding to controls inputs"


The reasons for 1 to 7 findings could be:
1. There are partial jamming and the helicopter is not able to maintain stabilization or autopilot commands ==> the stabilization deviation or the system deviation will activate TRIM and DAFCS cautions
2. The possibility that system EHSI #1 and #2 together with compass will come crazy at the sametime is impossible ==> the most likely the helicopter has been acting precisely as flight insturument's information to the crew has been or what they have been able to see on the instruments
3. The collective "heavy" and "the power dropping anytime he pulled to maintain power" ==> the most likely this indicates that the problem has been in Servo Actuators side because two independent hydraulic system will keep the hydraulic power needed all the time. The cause could be a partial "kick back of the ServoActuator channel I or channel II jamming (without any Servo Jam caution as onthe other cases has been).
4. The controls are not responding ==> the cause could be in the servo actuator (swash plate position is not in correct position as it should be for stady flight and the autopilot computer are indicating this as a deviation and activates TRIM FAIL and DAFCS cautions. This together with Sikorsky's Mixing Unitis really mixing helicopter controllability (if this was the case then the crewand all passengers are very lucky that the helicopter wouldn't come totally unflyable and the decision making by the Captain has been a brilliant life saving action).
5. "The cyclic not responding to lateral movement" ==> as stated on 4. and the FDR read out will have the readings of all controls position vs. the helicopter attitude and ....."
6. "Okey they lost all their instruments" ==> impossible situation for a Certified Transportation category helicopter and the loss of "magnetic compass"confirms that the readings has been the most likely correct behaving of the helicopter in IMC and the helicopter has been in partially unflyable (loss of controllability from 3000 ft. to 1500 ft.)

These findings 1 to 7 is not supporting the theory that the root case is TRIM FAIL or / and DAFSC FAIL. The most likely these cautions has come after the helicopter DAFSC system (autopilot computers are realizing that the control of stabilization has been lost) and the Autopilot computers has been generating these cautions.

The main question will be: What about hydraulic fluid contamination? If the cause is the jam in the Servo Actuators (e.g. pistons) the Teflon-Carbon piston rings will make the fluid almost immediately to look dark black and also some of the debris’s could be identified in the hydraulic fluid.

The root cause and consequences should be identified and separated. A lot of information could be picked up from the helicopter’s DAU, GPS/FMS, on other data systems which collects data in addition of the FDR and the CVR.

I would like to know: is the hydraulic fluid contaminated or not? This question NO or YES is very important to analyze the root cause and this information could be a very important for the future actions to maintain the safety of the crew menbers and the passegers.


I hope that I’m wrong!
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Old 18th Mar 2016, 22:42
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"Investigation so far discovered some defects with both the Cockpit Image Recording and the Flight Data Recording Systems. The Flight Data Acquisition Unit (FDAU) also indicated internal FAULT. A significant number of the parameters on the FDR data such as heading, cyclic, collective and yaw control inputs were not retrieved."

Hah, hah!

Sorry to say but not nothing new since 1979.
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Old 19th Mar 2016, 02:39
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What is particularly interesting is AP2 cycled off/on 5 times in the cruise at 3000' before the rapid descent, and AP1 cycled off/on twice over the same period. Both times AP1 went off AP2 also went off. That has to be an action of the crew, because whilst an AP can switch itself off for whatever reason (e.g. electrical interruption), the only way it can come on again is by pilot action. And both AP switching themselves off at the same time is impossible to believe.

AP2 is powered off the essential bus, as are the stick trims. Interruption of essential bus power the collective stick trim system no longer holds the collective in the set position and it will probably lower slightly. This is consistent with observation of the FP reporting to the Captain. Passenger reporting burning smell on the previous sector could also be indicative of an electrical problem. Spinning EHSI might also be indicative of an electrical problem (the report didn't mention whether both were spinning, I would be surprised if both EHSI were doing the same thing). The spinning compass makes no sense. The standby magnetic compass is completely removed from the electrical systems, it just aligns itself with the earths magnetic field and the aircraft pivots around the compass fixed in space. If the compass was spinning, it is the aircraft spinning around the compass. It is impossible to believe the aircraft was spinning.

Also the Captain report of the aircraft not responding to lateral cyclic movement is impossible to believe, unless the control itself couldn't move which would be indicative of a mechanical jam forward of the mixing unit, or a lateral cyclic damper jam. If the control moves but the aircraft fails to respond, a control tube has come undone and it would be impossible to land the aircraft.

Without the full set of FDR data this one will take quite a bit of thinking to sort out what was real, and what might have been confused.

I am wrecking my brains contemplating why a crew might switch an AP off/on 7 times during the course of a flight. Reason being. An AP that keeps turning itself off is telling you that it doesn't want to be turned back on again, so leave it off. Or, if there is an AFCS malfunction of some sort, if turning an AP off/on once doesn't solve the problem, turning it off/on another 2+ times isn't likely to result in a different outcome.

It is an onerous responsibility on a pilot to decide to land a $10 million helicopter on the ocean with 11 people on board, particularly for a Captain with only 306 hours PIC time. Very lucky that the sea state was calm.

Last edited by gulliBell; 19th Mar 2016 at 12:20.
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Old 19th Mar 2016, 19:41
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Same problem

I had same problem in one S76C+ in Nigeria also. 7000 feet IFR bad weather, both channels AP1 and 2 went to off at same time, I went down looking for VFR conditions flying with stand by horizon (analog), 300 feet I got VFR conditions, copilot tried several times to recover APs as emergency check list demand, pulling CB on top Pilot head, but never wait 5 seconds to back in, and then press APs switches, on VFR conditions we followed step by step emergency procedures, recovered the APs and back home (Port Harcourt)
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Old 19th Mar 2016, 20:50
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Originally Posted by picudo
I had same problem in one S76C+ in Nigeria also. 7000 feet IFR bad weather, both channels AP1 and 2 went to off at same time, I went down looking for VFR conditions flying with stand by horizon (analog), 300 feet I got VFR conditions, copilot tried several times to recover APs as emergency check list demand, pulling CB on top Pilot head, but never wait 5 seconds to back in, and then press APs switches, on VFR conditions we followed step by step emergency procedures, recovered the APs and back home (Port Harcourt)
AP1 and AP2 are isolated systems with different AP computers, different electric sources..... AP systems can't have any failure at same time (AP1 and AP2). It will be easy to understand that this dual AP failure is a consequence.

AP1/2 system will be automatically switched off if the autopilot systems electrical line actuators are not able to maintain selected couplings or if the autopilot system is not able to maintain helicopter's stability (AHRS information vs. helicopter selected heading and attitude is deviated).

The most likely the dual AP failure is a consequence and the root cause could be a blockage or a partial blockage of the flight control system.

Did you make an incident report of this dual AP failure? What was the company's conclusion for this event?

A half an year I was contacted by a pilot who has been able to follow very closely of two different events where (S76) the flight controls temporary jammed during flight. A few years later he was interested in to know what was the company's safety management systems conclusion of these two events. This major operator's (SMS) event dats base was clean and noboby could not memorized that these event has ever happen. It's like this FDR, FDAU, CAMERAS data are missing of 3rd February, 2016 accident. Coincidence?

12th August, 2016 S76C+ total loss of controllability! (six kills) Coincidence?

3rd February, 2016 S76C++ partial loss of controllability? Coincidence?

10th August, 2005 S76C+ total jamming of flight controls and total loss of helicopter's controllability (14 kills) Coincidence?

S76 helicopters are certified according Transportation category (FAA) and should not come suddenly unflyable without any warning - caution!
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Old 19th Mar 2016, 21:18
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The lesser of 2 weevils?

Picudo (Spanish for weevil)

Did your co-pilot try pushing the AP RESET buttons rather than "pulling circuit breakers on top pilots head"?

Then wait until the respective off flags had cleared on the respective EADI's before attempting to re-engage AP1 and AP2?

May have had more success!

Just a thought!

Trog
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Old 19th Mar 2016, 22:01
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@picudo. In that example, why did you need to fly on the standby attitude indicator? Are you saying you had a total loss of electrical power resulting in AP1/2 off and both EADI/EHSI off, etc etc?
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Old 19th Mar 2016, 22:16
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Much easy to me fly analog horizon with no APs than EFIS (very sensitive), if you have a chance try it to fly IFR conditions with no APs, with EFIS equipment, you will have a lot of fun. After that emergency CHC start to train crews in the sim with that condition, 90% or so inverted.
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Old 20th Mar 2016, 00:03
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I wasn't aware CHC were teaching that condition. I don't demonstrate or train AP off flying with students (either VMC or IMC) unless they can first complete all the other training sequences with both AP on. If we complete all the syllabus training within the allocated time to an acceptable standard then we will attempt AP off flying. I don't recall ever seeing a student get from IMC to VMC with both AP off. After double AP failure in IMC the students are usually totally out of control within about 10 seconds.
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Old 20th Mar 2016, 02:57
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AP1 and AP2 are isolated systems with different AP computers, different electric sources..... AP systems can't have any failure at same time (AP1 and AP2).
Yes they can, because I've had it. Trouble is, I can't recall the root cause (we're talking 20 or more years ago), but the regulator was wondering if the aircraft should be certified IFR capable with such a single point failure. Nothing eventuated. Contact with Australian ATSB or the CASA Moorabbin office should elicit a copy of the incident report.
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Old 20th Mar 2016, 03:19
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...simultaneous AP failure is about as likely as both engines failing at the same time, not something to be too worried about I should think.

In the Nigeria accident the FDR shows both AP were on when it ditched. I'm curious why they were flying/hovering around for 5 minutes at 25 knots or less when faced with a malfunction so dire that required a ditching: you'd think the landing profile would be more timely (unless it's a recording anomaly with the aircraft engines left running for a few minutes whilst in marine mode). This together with the seven AP2 resets and two AP1 resets has me quite puzzled.

Last edited by gulliBell; 20th Mar 2016 at 03:44.
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Old 20th Mar 2016, 10:10
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Much easy to me fly analog horizon with no APs than EFIS (very sensitive), if you have a chance try it to fly IFR conditions with no APs, with EFIS equipment, you will have a lot of fun. After that emergency CHC start to train crews in the sim with that condition
But not too hard to fly the EFIS AP out if you slow down to 120 knots, especially if you have selected the AP off so you know its coming.

I still see no real reason for a ditching here.
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Old 20th Mar 2016, 10:18
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Has there been any mention whether the CVR was operative? Or was it like the FDR, didn't record much of what it was supposed to record.
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Old 20th Mar 2016, 13:22
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@gulliBell
AP2 is powered off the essential bus, as are thestick trims. Interruption of essential bus power the collective stick trimsystem no longer holds the collective in the set position and it will probablylower slightly. This is consistent with observation of the FP reporting to theCaptain

This is not consistent with your conclusion of loss of the force trim. PF’s statement is “the collective being heady and the power dropping anytime he pulled to maintain power” and this doesn't support your conclusion that the case is the lost of the Force Trim.

The most likely scenario is the jamming or the partial jamming of one rod of flight controls. If one of the rods is jammed then the whole rod line is jammed. The jamming could be located in to the Mixing Unit, or before or after the Mixing Unit. If the jamming is in somewhere in the rod line of the collective then the collective movements are transferred via Mixing unit forward. Because of the collective rod line in not able to move (due to jamming) then the whole movement of PF’s collective will be transferred to be movements of the other freely moving flight control rods (collective rod line stucked or partial stucked).

If the case is that the “the collective rod is jammed” (doesn’t matter where) but still the collective is able to move even its feels very heavy (“The PF called my attention to the collective being heavy and the power dropping anytime he pulled to maintain power”). In this case the all of the collective movements has been transferred only to the Mixing unit’s compensating rods. Then the all movements of collective rod have been transferred in to Mixing Unit’s only the freely moving rods. These only freely moving rods will transfer PF’s control inputs incorrectly. This has the most likely caused the loss of the controllability of the helicopter.


It doesn't matter which "control rod line is affected" the Mixing Unit behaves like in the scenario of jammed collective rod. In every case the jamming on of the control rod line is "really mixing helicopter's steering and it will make the helicopter's flight controls to be illogical. This scenario will be the most likely and it will lead to the loss of the helicopter controllability or partial controllability and to the situation where the helicopter is unflyable.

@gulliBell
...simultaneous AP failure is about as likely as both engines failing at the same time.
I agree that! It is possible to lose both of the AP's at same time. It will be very likely in a case where e.g. the flight controls are jammed or partial jammed. In this situation where the helicopter AP computers / electrical line actuators are not able to maintain a helicopter's stability or AP computers commands to the line actuators has lost. If this is the situation then the AP1 and AP2 will be kicked off immediately (ATT and SAS modes).

I assume that the "loss of the autopilots" means in this case that they have lost the both of ATT and SAS modes?

These both scenarios are logical, and it will not be a surprise to for certain S76 accident investigators of accidents which have occuered in tha past.

Last edited by Copterline 103; 21st Mar 2016 at 15:10. Reason: Typo corrections
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Old 20th Mar 2016, 13:41
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@megan
Yes they can, because I've had it. Trouble is, I can't recall the root cause (we're talking 20 or more years ago), but the regulator was wondering if the aircraft should be certified IFR capable with such a single point failure. Nothing eventuated. Contact with Australian ATSB or the CASA Moorabbin office should elicit a copy of the incident report.
I did that already 2008. I got the incident report and other related material from Australian ATSB.

Think about it? Is this event to the lose of Dual AP's a root cause or is this the consequence? For me it was very clear after receiving these Australina ATSB's document which was verified and evaluated together with the other non-public documents which were on my hands.

This is a known issue in general but the all related documentations are non-public and classify. You can wonder why?
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Old 20th Mar 2016, 14:40
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@Copterline 103. I disagree with much of your #505. The PF reporting heavy collective doesn't mean he needs more force than normal to move the collective, it's just his way of expression to describe the collective not remaining where he left it (because the collective force trim is no longer holding it in position).

Binding in the controls must be before the mixing unit if only one axis is affected, in this case only lateral control problem was reported. There is nothing I've seen here to indicate any binding in the collective, and nothing to indicate any hydraulic servo actuator problem.

I do not see anything to suggest the AP turning itself off (due to flight control binding or whatever). The FDR shows the AP turning off and then back on again within only a few seconds, which to me says the AP turning off was by pilot action (in all 9 instances). I would expect to see FDR data show the AP off for a much longer period before coming on again if it had turned itself off, because generally it takes pilots a while to notice that a single AP has dropped off.

The AP were never lost, the FDR shows they were on all the time (except when they were cycled off/on several times presumably by pilot diagnostic action).

Obviously something happened to spook the crew, my bet is an electrical gremlin of some sort got interpreted as a mechanical problem. A crew wouldn't ditch a helicopter for an electrical problem unless it was an electrical fire that couldn't be contained following emergency checklist action. The salt water bath all the electrical bits and pieces received wouldn't be helpful for replicating the problem, but the cause of a burning smell reported should leave some physical evidence in a loom or other component that an investigator could find.
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Old 20th Mar 2016, 23:50
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@gulliBell
Binding in the controls must be before the mixing unit if only one axis is affected, in this case only lateral control problem was reported. There is nothin
I have been able to study Sikorsky’s GEN HEL Simulator data together with the integrated EASY/ADAMS modeling analyzes. This modeling will explain how the S76 series helicopter‘s flight control systems behaves in certain situation and how the aerodynamics behaves on these situations.

Before Mixing Unit there are four different rods which will bring PF’s controls inputs to the Mixing Unit. The PF’s controls inputs are shared with the all other dimensions inside the Mixing Unit (lateral servo bell crank, the aft servo mixer, the collective pitch mixer, and collective roll mixer and the forward (quad) yaw angle). After the Mixing Unit there are three control rods which will transfer control rods inputs to the three Servo Actuators (via three control rod tubes, each one to the each Servo Actuator).

In the past the accident investigators have been able to simulate a blockage of some of the control rods by using this GenHel simulator and ADAMS –EASY5 software modelling. The test findings were that if one of the rods is blocked by a locking pin (which means that the whole specific rod line is blocked). After this simulated blockage the investigators made a simulation by the GenHel / ADAMS-EASY5 simulator – modeling. The simulation was run for 11 seconds, 1100 output steps, completing the full simulation.

This GenHel simulation data has been compared to the FDR’s print outs. The simulation data was fully matching FDR’s data from the 10th August, 2005 S76C+ accident in the BalticSea.


I have good understanding how the S76 flight control behaves and what are the consequences and what is the root cause. Due to this I will still keep on my opinion and understanding how the S76 helicopter behaves and what might be the cause why S76 will come unflyable (if it will come unflyable, and how the helicopter will lose its controllability).

QUICK READ OUT FROM THE FDR’S PRINT OUT
The latest accident data 3rd February, 2016 (the parameters which was recovered from FDR data base) shows that the event has been started by a slight increase of IAS to 130-135 KTS (cruising speed has been a steady 125 KTS) and which after by pitch up (about +250 ft).

During next minute the helicopter ISA has dropped down to 90 KTS and the helicopter has started to descent.The descent rate after one minute after the event has been started was averagely –2100 ft. per minute but the last 40 seconds the descent rate has been almost double (4000 ft. per minute). During these first 20 seconds the IAS has been around 90 KTS but during the high rate of descent about 4000 ft. per minute the IAS has increased up to 148 KTS.

When the helicopter has reach 1000 ft. and immediately after this the helicopter has gain an additional altitude of + 500 ft. During this climb the IAS has drop down to 64 KTS. During these first two minutes the both of AP’s has been switched on and no MASTER WARNING or any CAUTION has exist. After these two minutes MASTER WARNING has illuminated for next 60 seconds without any CAUTIONS. The event has lasted an additional 20 minutes. The FDR data shows that the crew has had difficulties to maintain a constant IAS. The IAS has been fluctuated during the last 20 minutes. During the whole event the both AP’s has been switched on excluing on reset of AP1 and two reset of AP2 (this resets has happen about 10 minutes after the event has started when the IAS has been about 80 KTS and the ALTITUDE 1200 ft.).

It looks that the cruising IAS has been 125 KTS all the time since the helicopter has reach 3000 ft. altitude. Is this 125 KTS Bristow Company’s operating speed for S76C++ helicopter? Or is this an indication that the crew has already prepared to be faced some difficulties? Maybe due to the AP1’sand AP2’s repeated disengagement the crew has decided to use reduced cruising speed???
Whatever is the cause for this ditching this accident together with the other related accident is aserious situation for the S76 series heliopter. The future operation of S76 series helicopters will insist that this and the other accidents and quite many related incidents are carefully investigated.

I’m wondering how and why the FDR, FDAU and cockpit camera systems all data could be lost? Also the information of hydraulic fluid condition could be very valuable information to verify if the Servo Actuator’s do not have any inclusion. The information that the hydraulic fluid is clean or the hydraulic fluid is contaminated will be very important information for the decision making to maintain crew and passenger safety.

I hope that I’m wrong but all the facts and the knowledge are supporting my conclusions. Everyone have a right to have their own opinions and their own assumptions. I’m ready to defend my views if needed. I'm pleased to give more specific information if needed?
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Old 21st Mar 2016, 01:38
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This is a known issue in general but the all related documentations are non-public and classify. You can wonder why?
No imagination needed Copterline. Following an engine failure (76 Turbomeca) the authorities voiced opinion that certain oil lines didn't meet certification standards. Don't think that went anywhere.
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Old 21st Mar 2016, 08:25
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@TroyTempest
Why can't Sikorsky or Bristow issue something to keep us at ease?
There are so many parties who have "the own dog in fight". This "development" has started already since 1979. It looks that nobody couldn't jump away of this "development" because the speed has been accelerated to be high enough...

Sikorsky Aircraft Corporation is not any more involve this because Lockheed Martin bought SIK about three months ago. The transaction volume was 9.000.000.000 USD cash. This deal closing was made three months after the first Bristow Nigeria S76C+ accident where the helicopter come unflyable and six people died.

Bristow has still about 80 units of S76 series helicopters in daily operation.

I hope that will clear the picture?
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