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Bell 412

Old 2nd Nov 2004, 23:33
  #41 (permalink)  
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Nigerian Expat Outlaw,

I guess I wasn't clear enough. The third engine costs so much in lost range, and gains so little in safety (arguably zero) that it is totally rejected by all commercial opeators. The newest commercial jets are all 2 engined for that reason as well.

SASless, the OEI capability of the S-92 allows about 330 NM from a rig at zero wind on an ISA+10 degree day with full pax and baggage, which is great. If we loaded it to enroute OEI, the aircraft would have about 1000 lbs more payload. That is the price paid for the full OEI. The military H-92 has the same systems, and loads up at 2100 lbs more payload. That 1/2 to 1 ton loss is the "cost" of full Cat A.

That being said, our job at any manufacturer is not to argue with the customer, it is to deliver what he wants. Since full Cat A is so popular 9and was required a few years ago) we designed it in. But we made the EGPWS standard just for real safety.
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Old 3rd Nov 2004, 00:21
  #42 (permalink)  
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Interesting point you made....Ground Proximity Warning system shoved onto the customer by the manufactuer....rather than by the Customer demanding it. That system would have saved at least one S76 in the Gulf of Mexico this year....and a bunch of lives. Funny how the Big Time corporate helicopters get outfitted with all the gadgets while the Offshore birds do without. I guess all the IFR flying in the Northeast corridor requires that stuff and the Gulf of Mexico doesn't.
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Old 3rd Nov 2004, 02:43
  #43 (permalink)  
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I have to agree with Nick. If you look at accidents here over the past years, engine failures in twins are not killing people. Flying into the water, into rigs, into thunderstorms, etc are killing people. Mechanical failures of other components are killing people, and merely frightening others, because of the skill of some pilots. I'd far prefer an engine failure to a tail rotor failure.

I don't spend much time worrying about an engine failure, if any, except on checkrides when I know it's going to happen. A simple engine failure enroute is an annoyance, nothing more. On takeoff it can be critical, but it seldom happens there, despite what anyone may want to believe. Look at all the reports you want, and you will find very few in which an engine failed on takeoff. There have been none at all that I know of in which the result was the tail hitting the heliport. Focusing on engine failure to the exclusion of all else, especially to the exclusion of CFIT, is incredibly short-sighted.

And now back to your regularly scheduled hand-wringing.
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Old 3rd Nov 2004, 04:11
  #44 (permalink)  
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Does the S92 have TCAS or similar and HUMS as standard fit?
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Old 3rd Nov 2004, 05:05
  #45 (permalink)  
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HUMS is standard, TCAS is available. See
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Old 5th May 2005, 07:15
  #46 (permalink)  
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Bell 412 question

We operate the Bell 412 EP in a variety of roles and have a question regarding the pre flight hydraulic systems checks.

According to the Bell flight manual there are 2 checks to be carried out. The preliminary check with the throttles at idle to check for uncommanded control movement or motoring whilst either system is selected off and a second check at 100%rpm to determine proper operation of the hydraulic actuators.

During the second check you are also required to check the electrical interlock, which prevents both systems from being switched off at the same time. To do this you are required to select the second system’s switch to off whilst the first is already isolated to check that the second system remains operational and vice versa.

For those of you not familiar with this aircraft the hydraulic switch panel is located on the centre console on the co-pilots side. Therefore as we operate the aircraft single pilot, this check is conducted with the left hand away from the collective.

Our concern is that whilst the likelihood of this electrical interlock failing is no doubt extremely rare, if there is a check in place to ensure the interlock is working then logically there must be a risk of it not! As the procedure stands if it did fail the aircraft would have no hydraulic assistance at 100%rpm and the collective unguarded.

Our question is could the interlock part of the second hydraulic check be carried out during the preliminary hydraulic check when the throttles are at idle?

Are there any other 412 operators out there who share our concern or are we being over cautious?
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Old 5th May 2005, 08:03
  #47 (permalink)  

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I may be wrong (and I'm sure I'll be corrected if I am !!), but we do another check at idle called a "Stick Jump" check which should give the pilot some assurance that your scenario won't happen.

All we do is switch off each system in turn while guarding the collective with our knee, i.e. both feet are still on the pedals but the left knee is bent over to prevent the collective rising uncommanded. This is done at the same stage as the "Creep Check".

Hope this helps.


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Old 5th May 2005, 10:42
  #48 (permalink)  
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On the second check, if both systems fail, it won't matter if your hand is on the stick or not. If it doesn't move, no problem. If it does move, you won't be strong enough to stop it. Your instinct then should be to undo the last switch selection you made rather than fighting the controls.

What you should do is keep your left leg lightly touching the collective so that you can feel if there is any unusual movement.

I doubt if the check is valid at low rpm because the loads are appreciably different. If it is valid, the possible uncommanded movement of controls at low rpm could be quite damaging.

I'd recommend sticking to the manual.
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Old 5th May 2005, 10:48
  #49 (permalink)  

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Ah ha. That makes sense to me. Thanks a lot.

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Old 5th May 2005, 13:07
  #50 (permalink)  
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This does underscore the question of exactly how often you must check things to see if they are broken. Considering the very low failure rate of hard wired switches, you must wonder why you check that interconnect every day.

I have always wondered exactly how much time we waste in the cockpit doing daily checks that could be done weekly or monthly or yearly, depending on the inherent reliability of the system being checked. As manfacturers, we are stuck because there is only one paper checklist, with the "first start of the day" and the "through flight" checks.

With computer cockpits, it should be possible for the manufacturer to group the system checks by prompting you to do the required check on the required interval. This could allow a much briefer checklist.

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Old 5th May 2005, 13:31
  #51 (permalink)  
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How would you differentiate between 7 starts and shutdown in a day, and 7 days of one flight each?

Slightly off topic, but if you do the hydraulic check in the 212 at 100% Nr but turn off an engine governor switch instead (very close to Hyd panel) it will wake you up very quickly!
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Old 5th May 2005, 16:13
  #52 (permalink)  
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SP, you have a good point. If the loss of hydraulig pressure would cause an abrupt movement of the controls I would rather be at idle than at 100% Nr.
Trusting the Bell engineers, the explanation must be that there is no significant feedback from the rotors if hydraulic pressure is lost.
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Old 5th May 2005, 16:37
  #53 (permalink)  
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I don't have a checklist in front of me, but I believe the initial check is every flight and the full check is first flight of the day.

I completely agree with the comments about scheduling the checks. We've seen a reduction in certain parts of maintenance by reducing the scope of pre-flight checks. If you open one panel four times between each flight, not much will change, but the closures will certainly show more wear.

I wouldn't be surprised to see similar results with some of the cockpit checks that are done.
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Old 5th May 2005, 17:02
  #54 (permalink)  
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To continue from SP's initial post...The resting position for a 412 collective is around 1/2 travel, which is where it naturally goes to once hyd assistance is removed; I would assume this is the neutral position for the elastomeric bearings. If all hydraulic assistance is removed when at 100% NR, will the collective naturally revert to this position ? If this is the case it is extremely unlikely that any pilot would be able to stop it due to the forces involved.

The flight manual warns that flight with no hydraulic assistance is not possible (no surprises there!). Therefore why do we carry out a check that if succesful (ie the check proves there there is a malfunction) will potentially make the aircraft uncontrollable, possibly leaping into the air?

answers on a postcard....
detgnome is offline  
Old 5th May 2005, 17:11
  #55 (permalink)  
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You’ve probably already done this, but…

Try contacting the BHT rep for your area; you can find them through the Bell website . If they don’t know the answers themselves they’ll certainly know whom within Bell to ask and both BHT reps I’ve had occasion to deal with myself couldn’t have been more helpful. Alternatively, if one of you is going to the factory school soon, this would be great discussion fodder for the class and instructor.

As an aside, and following Nick’s point, I remember reading an article about tech delays on the USAF C-5 Galaxy fleet – the majority of which were due to the Air Force insisting on exercising emergency systems each flight that had been designed as emergency systems, i.e. for one-time use…
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Old 5th May 2005, 18:04
  #56 (permalink)  
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I am not a Bell rep so the information below is worth what you paid for it.

1. The check at idle checks the timing between the two systems pilot valves so that you know that one hydraulic system is not fighting the other. As you know the servo is actually two servos mounted together and redundant. If the timing or pilot valve centering is not the same, when you turn off one system the control will jump the distance needed to recenter the pilot valve.

2. For the check at 100% you needn't be concerned about the controls jumping as you have already confirmed this at idle. The real check here is to ensure that you can't turn off both hydraulic systems at the same time. Bell wants to make sure that you can't turn off both hydraulic systems by mistake. This has happened in the past via improper maintenance or other items installed by people that supply the necessary ground in order to turn the system off. When you turn off the hydraulic system you are actually powering the solenoid valve to the off position. Hyd #1 valve actually supplies the ground for the #2 valve and #2 supplies #1's ground. That way if one system is already off, then the other system can't be turned off unless the original system's switch is positioned back into the on postion. By using power to turn the system off, acts as a fail safe, so that if you loose all electrical power you won't loose hydralulics. As you know the 412 can't fly without the red stuff flowing through its tubes...
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Old 5th May 2005, 18:38
  #57 (permalink)  
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I know this is strictly off topic-but why do Eurocopter not install hydraulic cut-off switches in the 355/365-how could you isolate a possible restriction?
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Old 5th May 2005, 19:27
  #58 (permalink)  
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Both the preliminary and the full check are done on the first flight of the day, not every flight. And as to Nick's question of why they need to be done that often, I have no idea. Obviously Bell has some concern about it, but I've never been able to turn off both systems at the same time. There are a number of systems checks in the 412 that seem rather needless to me, but they're on the checklist, so I do them. The 412 hydraulics check is little different from the S76 check, and that is done daily also. Total loss of hydraulic power is one of those things that will kill you, unlike engine failure. It's obviously not likely, but the check only takes a few seconds, so I don't worry about it.

As for Scorpiones Pungunt's original question, I don't think you will have a serious problem on the ground, as long as the controls are neutral or very close. You wouldn't be able to move them, but on the ground you don't have to. I'm not sure there would be that much difference between 80% and 100% Nr anyway, and 80% is the minimum RPM for a 412 (another consequence of the remarkably poorly designed main rotor system). In general, I think it's a good idea to do things the way the manufacturer recommends, because there is usually a good reason for doing them that way.
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Old 5th May 2005, 21:13
  #59 (permalink)  
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Ah yes Hammer Headed, don't forget you are talking about Bell where evolution not revolution is the way of life! I'm told that the handle on the tail boom baggage door on the 412 is the same as the handle originally use on the Bell 47!

Anyway, back to the discussion. My point is that whilst testing/checking a system is fine, in the case of the Hyd system interlock failing at 100% NR, what is the outcome? Nobody seems to have a definitive answer and I am still not convinced that the cab will still sit on the ground and not thrash itself to death. If this is the case does it not question the validity of the check in the first place?
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Old 6th May 2005, 00:31
  #60 (permalink)  
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"detgnome" you know Bell keep´s it simple, if it ain´t broke don´t fix it

I see many comments telling to stick to the manual... but I wonder how many PT6´s have been incinerated due to that HYD test at 100% because the GOV Manual/AUTO switch was moved instead of the HYD switch which is just above.

The 212 has no hyd system isolate function as it can be flown with both hyd system´s off (its tough, yeah I know) and I really can´t see the point in the test at 100% except make more money for Pratt & Whitney.
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