cpt ,
CVR was explaining what was on going in our accident. Flight Controls were stuck and the crew was fighting and making all the efforts to get these stuck controls to move.
The crew broke the top of collective when the captain was trying to got fully (max) up position standing collective down. Also the crew was using all available hand power to move cyclic stick. Pilot’s side cyclic stick was bended forward. The connecting Rod (connecting pilot and co-pilots controls was separated (the tube and the Rod end).
The design of the flight controls tubes and rod ends are designed to be used in normal condition. In normal conditions there is no major load at all. These tubes and control Rod End are not designed to be fail safe with a power what could be used by two dying men. The basic assumption is that (FAR29) redundant Servo Actuator systems should not be stuck.
I can sent an email to you and attach NTSB’s ADAMS HYDRAULIC SIMULATION. There are scenarios where one C3 return port is blocked and the second simulation is that the both of these C3 return ports are blocked.
The scenario of one C3 is block will make Forward and Lateral Servo Actuator full extension within 3,5 seconds. If the both C3 ports are blocked then the Forward and Lateral Servo Actuators full extension will happened within 1,5 seconds.
Simulation affect (air speed 0,8 VNE and G force 1,0 cruise flight phase) is that when Servo actuator is fully extended then the helicopter will pitch up 60 degrees, banking to the left, at the beginning turning to the left which after (the collective is max up position then mixing unit will mechanically put the right pedal in fully right down position. After this helicopter will start to spiral to the right.
NTSB Servo simulation found out that Lateral Servo Actuator is under very heavy stress (load). The NTSB test report shows that, the stress force will variate between -1400 LBF to -400 LBF. This variation is very quick to fluctuate. It will fluctuate from high -1400 LBF (equal -6227 Newton) to -400 LBF (equal -1779 Newton) average 8 times every second.
If you will study an accident in Sutton, USA in 1986 the root case for accident is unknown. The S76B helicopter was cruising at 6000 ft. The crew was two Sikorsky’s test pilot and two Sikorsky’s technicians. Suddenly helicopter came unflyable. The radar recording is proving that helicopter speed, heading start to variate quickly. The helicopter was losing the speed and turning to the left. Very soon after this helicopter was starting to spiral to the right. The rate of decent was about 3000 ft/min. At time when this S76 hit to the ground the impact attitude was 12 degrees bank to the right and nose was at zero level. The Baltic Sea accident rate of decent was 3000 ft/ min and when the helicopter hit to the water it had 12 degrees right bank.
We all know the law of aerodynamics. If the conditions are same the result is always the same.
It is very interested in to see all the data from Lagos. Flight data recorder and CVR recording will tell within five minutes what this case was. ICAO ANNEX 13 procedures should bring Interim Accident Report to be published within 30 days. What is the reason for delay?
FAA has issued an EAD. My opinion is that the Jam nut is not the issue at all. It idea of Jam nut in this Control Rod tube / Rod End is only for to keep this Rod assemblies length stuck at time when the Rod assembly in not connected to the helicopter flight controls, mixing unit or the Servo Actuators. When Rod Assembly is connected by locking bolts (by each end) the Rod end is not able to rotate. If the Jam nut is totally missing or if the Jam nut is in its place with safety wiring there is no change of strength of the Rod assembly.
The other end of the Rod tube and Rod end is riveted (fix installation). Also the other Rod end is a fix installation due to the bolt connection (Servo Actuator). This makes impossible that the Rod End can be rotating (loosens or tightens).
I don’t understand how this Jam nut could be a case at all? And what is the point of this EAD?
The crew had 37 seconds time to try everything to have helicopter be a flyable helicopter. During this 37 seconds time the helicopter was spiraling to the right 13 times.
There is a procedure to get an unflyable helicopter back to flyable if this stuck controls case happen.