Eyewitnesses vs. FDR / Banging sound/ Spinning left / MR RPM zero
Given by eyewitnesses statements should be treated with caution.
Trusted from information seems to a loud bang sound and helicopter spinning before hitting the water with M/R RPM zero or almost zero..
The best source of information is the FDR which explains in detail where it all began and where it all ended.
In my assessment, the FDR will indicate that the cyclic has become fully aft position, collective has risen to max top position within one second.
No warning or caution has existed when the situation has started. The first warning probably had been a low M/R RPM. This is due to the fact that the helicopter nose will rise up to 60 degrees (stalling and making a banging sound), banking 50 degrees to the left. Cruising speed 140 kts to zero will be lost in a second. Flight controls are stuck by one servo actuator which is stuck in fully extended position. (Sikorsky’s flight controls system has mechanical mixing unit. This mixing unit will reduce pilots work load by mechanical compensation to peals when the collective will be increased or decreased). When the collective is in a fully up position the helicopter mixing unit mechanically makes compensation and will put left pedal almost max left position (causing spinning to the left after helicopter has lost its airspeed).
The reason why helicopter is losing its M/R RPM it is most likely due to collective position which remains max up position due to 3500 PSI hydraulic pressure. Even both of Turbomeca’s ARRIEL 2S1 engines are in “fly-away emergency power” but engines don’t have enough power to maintain MR RPM due to collective remains in max up position. The crew doesn’t have any possibility to fight against 3500 PSI hydraulic power which is over controlling all controls keeping cyclic in full aft, collective max up and mixing unit is compensating collective position by taking left pedal almost fully down.
All this causes the Servo Actuator piston’s chipped plasma coating what will block Servo Actuator’s C3 return port (fluid) or both of C3 return ports. Servo Actuator system or system design does not recognize that the Servo Actuator has failed and there is not any auto function which will release affected servo channel. Servo Actuator’s design can’t recognize that servo actuator has failed and the whole Servo Actuator unit (two independent Servo Actuators) is out of control. During this situation there is no any Servo related cautions or warnings. This single defect will cause that the helicopter will be immediately unflyable.
It is clear that the transportation category’s helicopter type certification requirements requires that any single defect (e.g. chipping of the plasma coating) wouldn’t drop any offshore approved transportation category helicopter down. That's what has happened to us 10th August, 2005. Our helicopter s/n was 760512 (made 28 units before that Bristow’s s/n 760540). All information what I have received are supporting theory that “the most likely” this will be also the case in Lagos.
FDR's data will tell immediately what has happened.
In our accident August 10th, 2005 we lost 14 innocent lives.