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Old 6th Dec 2001, 20:39
  #36 (permalink)  
Lu Zuckerman

Join Date: Sep 2000
Location: The home of Dudley Dooright-Where the lead dog is the only one that gets a change of scenery.
Posts: 2,132

The reason I mentioned the Robinson head (tusk) in the same post with the AS-350 Jack stall problem was that if you do not comply with the POH limitations you can experience a problem. How severe that problem is on the AS-350 with jack stall is totally dependent upon the conditions under which it is experienced. We already know the seriousness of the problem on the R-22 and the end result of exceeding the POH instructions.

As an RMS engineer I would think that if this condition was known at the onset of the certification process then from a safety point of view they should have eliminated the problem through redesign of the hydraulic system (if that is the root of the problem).

Here are several questions, which relate to the R-22 but are directed towards the AS-350 jack stall problem.

1) At what point in the certification process was the problem identified? Was the limitation placed in the POH and the jack stall warning light installed on the instrument panel at service entry?

2) If it was not identified in the certification process then at what point after entry into service was the problem identified? When was the warning light installed

3) At what time was the POH modified to reflect the problem and establish the flight limitations?

4) How is the jack stall light turned on? Is it by a G sensing switch or a pressure switch in the hydraulic system? Or, is it by some other means?

5) If the problem was identified after service entry was any attempt made to modify that part of the system that allowed jack stall to manifest itself?

Regarding the statement about the servos being necessary to support the AFCS or any other electronic system that requires hydraulic boost most of those helicopters had these systems installed as after market items. On those helicopters (large) that have this type of system the electronically controlled servo valves are installed directly on the servo or on systems like those on some Sikorsky helicopters there is a primary and an aux. servo system and the electronic servo valves are on the aux. servo. On the EH-101 they have dual servos at the swashplate and the electronic control is incorporated as a part of the flight control linkage. This is similar to smaller helicopters that had the system installed during production and as after market items.
However the servos are not installed to support and AFCS their primary purpose is to resist and overcome feedback forces at any level.
Even though the AS-350 can be controlled without hydraulic boost I would question what the POH indicates if you encounter this condition.

Anybody that has the knowledge please respond to the questions above.
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