Originally Posted by
Fly Aiprt
This is an interesting question.
1) It appears that the manufacturer's document are not clear about the aircraft actual control forces.
2) In any hydraulic actuator/cylinder, the force is proportional to the fluid pressure acting upon the piston part of the actuator.
For the control force to be only doubled when pressure is actually fourfold, a device must be provided that reduces the force from the actuator to the control column.
As the 737 is a mechanical airplane, such a device - if it exists - should also be a hydro-mechanical unit.
Now what would be the point of increasing hydraulic pressure just to reduce its effect on the control system ?
No doubt some Civil Aviation Agency - and maybe even the FAA - will ask that the actual control forces and torque on the trim wheels be measured before drawing any conclusion as to the plausible scenario of the accidents or the 737 return to service.
I agree that there is conflicting information in the tech manuals, and I've asked our fleet managers to seek a correction. That being said, it is entirely possible that the force reduction is simply a consequence of the mechanical linkages (i.e. levers, gear or pulley reduction, etc) built into the system and is thus transparent to the pilots. I have been told that the pull force required on the control column should never exceed 50 lbs. Hopefully the accident investigation boards will include this issue in their investigations.