Bristow S76 Ditched in Nigeria today Feb 3 2016

[Copterline 103]

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!