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WNBC AS350BA Final accident data released

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It's sad that a basic hydraulic failure seems to be the cause of that accident. I have limited time in Jet Rangers and R44 Ravens (about 40 hours) - in both of those aircraft, hydraulics out is serious, but also very recognizable and not something that will cause you to lose control. I have never been in an Astar, but it seems that the combo of a belt-driven hydraulic pump and unforgiving hydraulics-out operation is an issue worth considering.

 

I remain both glad and amazed that no one was killed in that crash, and I am reminded of an old Peanuts comic strip. It starts out with Charlie Brown blowing soap bubbles. Snoopy runs and catches one of the bubbles in his mouth. He turns and with the intact bubble begins to trot confidently back to Charlie Brown. After a few steps he trips, bangs his chin on the ground and pops the bubble. This prompts Charlie Brown to look at Snoopy and say "You’re the only dog I’ve ever seen who can be deft and clumsy at the same time."

Edited by flingwing206

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The reason this aircraft lost hydraulics is because the belt failed, the R-44 and 206 hydraulic failure is no big deal. The Astar is an absolute armful, the fact is that this was a simple problem, the RFM calls for a run on landing.

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However, subsequent review of work orders revealed that the hydraulic pump drive belt was replaced on October 13, 2003, 442 hours prior to the accident.

 

However, they did not upgrade to an improved belt/bearing/pulley as recommended by a service bulletin. That may (or may not) have contributed.

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The report implies that the belt was improperly installed, and that it is unknown who installed the belt, since it wasn't logged in the MX log.

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True, but none of us are qualified to make that inference from this report. There wasn't enough information about the belt given to make that assessment. They only said that it was broken at the seam.

 

They also state in the report that in installation instructions supplied with the belt are inadequate (paraphrased), that they only state to point the arrow in the direction of rotation. According to the report, no information about tensioning or specific installation procedures are specified.

Edited by PhotoFlyer

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Glad no one was killed especially given such a spectacular wreck.

 

The Astar's Hydraulic Failure Procedures seems to pop up quite a bit in discussions.

 

I still believe that the training should be changed. When I started flying Astars 15 years ago the company's training pilot had me doing (all with hydraulics OFF) full traffic patterns, with landings, 90 degree pick ups and set downs, and then another traffic pattern followed by flying the Astar as fast as my arms could hold out so I could see how hard it is to fly past 100 knots.

 

Other companies I have worked at have said that is not required. A running landing (or run on landing) is all that you need to do when the Hydraulics Quit. I believe this is not a safe practice. Knowing how to hover an Astar without Hydraulics will change the outcome of many hydraulic failures. I have had 3 hydraulics failures in Astars and they can be hovered (all my failures ended back on the ramp without any damage.) Don't spend a lot of time picking your spot, don't get cocky and don't try to set down on helipads or hover holes; but the Astar is controllable in zero speed flight without Hydraulics (in most situations. i.e. if you are slinging a drill and have a loss of hydraulics: good luck).

 

That being said, the NTSB report sounds as if the pilot may not have dumped the hydraulics. That would make it nearly impossible to fly. I'm not sure if this is really what happened (the report sounds confusing still) but that would explain why it was very erratic to fly (servo assist one direction and hard cement the other as the accumulators ran out unevenly). The pilot still did one hell of a job to even get that aircraft to crash upright on a building if he was flying with only a couple servos getting pressure from the accumulators.

 

Another note: The intermittent horn shows signs of hyd pressure fluctuations. A slipping hyd belt could have caused the pressure changes. (intermittent horn in a B2 is a rotor over limit but this was a BA)

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The specifics of installing that particular belt are vague, according to my mechanic. There are directions as to proper tensioning of the belt, but they're indirect. The new belt is marked with two indexes at a set distance, installed in the direction of rotation appropriately indicated, and with the arrow outside. The belt would appear identical to casual inspection inside and out, excepting this mark. Once installed over the pump pulley, the pump is moved outwards until a specified distance is achieved between the marks made pre-installation. At that point, the belt is deemed properly tensioned.

The belts stretch with wear, so it's wise to check tension every time you inspect it. My pilot rule of thumb for proper minimum tension is that turning the pulley forwards must drive the main rotor, while turning backwards might not.

 

As to this event:

The fact that a belt change seems to have occurred without being fully documented is troubling. Add the fact that nobody seemed to have had a clue as to the belt's proper installation is also troubling. The fact that nobody sought guidance in the issue is damning. It appears this is an operator with poorly trained personnel and negligeable oversight.

There's been enough accidents following actual hydraulic failures in Astars that I believe many- if not most- pilots aren't being properly trained to deal with the situation. My opinion is that this pilot was not sufficiently trained in aircraft inspection, either.

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There seems to be quite a few hydraulic failures in this A/c. Has EC addressed the problem? How common are hydraulic failures in all A/c? What A/c have the most reliable hydraulics?

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I've worked on Astars for over 15 years and have seen only one broken belt,and have communicated to the tech rep how the installation is vague and especially the retensioning,He told me about redrawing the 100 mm lines again,and tightening the 3% and I asked where it said that cause no one I've met heard of it.and suggested they address the issue,people are always washing the transmission bay without covering the belt or checking the twang with greasy fingers causing the belt surface to loose traction,but no one seems to worry about it either.We have played with the hydraulic's capability on run down and the feel is there at even 30-40 rpm.so I think it has the capacity,but if a belt slips???we grab the pully and twist it to see it the rotor turns,and show the pilots what the twang noise should sould like on a retensioned belt.and it is up there in pitch..

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