Originally Posted by
glendalegoon
JRBarrett thanks for the great info do you know if there is a control lock that might not have been disengaged? wondering also if ther emight have been a major airspeed indicator failure (mind you, we are taught to rotate regardless of airspeed in the last 1ooo' of runway in certain circumstances)
Yes, there is a control lock - it is a red lever on the center console that is engaged by pulling it up to a latched position. It will lock the ailerons, elevators and rudder.
While the lock is fine for preventing the control surfaces from moving in gusty winds, it is not all THAT durable. The locking mechanisms could be easily overpowered (which is to say broken) by the power available to the control surface actuators once hydraulics come online.
For that reason, releasing the control lock is called out in the BEFORE starting engines checklist, as breaking the locks is a definite possibility once hydraulic pressure builds up, if an attempt is made to to move to move the yoke.
There is also a checklist requirement to test the stall barrier (stall warning) system before flight, after engine start. This entails pulling the yoke full aft, while the PIC and SIC, simultaneously press test switches, (each on their own side of the cockpit) for several seconds. This tests the AOA sensors, the stick shaker, and (lastly) the hydraulic stick pusher. Again, it would be impossible to perform this op test with the control lock engaged.
The ailerons and elevators are mechanically controlled via standard cables, pulleys, sectors etc. Ordinarily, the cables also control the hydraulic boost actuators at the control surfaces, but even in the case of a dual hydraulic failure, the controls would go to full mechanical reversion, meaning the surfaces can still be moved solely by pilot "muscle power" - Although it would be like manhandling a Mack truck without power steering, it would not be like losing all hydraulics in a purely FBW aircraft.
The GIV is not particularly "touchy" about elevator trim either. Some aircraft require the trim to be set to within a degree (or less) of a pre calculated value before takeoff, based on current CG. On the GIV, setting the trim to "somewhere in the general vicinity" of 10 degrees is usually perfectly fine. Which is to say that the "green band" on the trim wheel is quite wide.
Horizontal Stabilizer trim is a different matter though. The entire H-Stab moves progressively leading-edge down, automatically as the flaps are deployed. On the GIV this is accomplished by a rotating torque tube, running up the inside of the vertical stab, that is driven by the same hydraulic motor that drives the flap jack screws.
On later-model Gulfstreams, the H-Stab is driven by its own actuator, which is independent of the flap drive actuator.
Not being a GIV pilot, I am not sure what effect on pitch authority would result, if for some reason, the Horzontal Stab did not move to the proper position for the selected flap setting. I can think of several ways such a failure could occur from a mechanical perspective. The flap position indicator on the flight deck is a dual gauge, which shows both flap and H-Stab position, but am not 100 percent sure if an H-Stab not set properly would generate any other config warning (I.e. CAS message etc.) on the GIV. I'll have to check my maintenance manuals tomorrow.