Bell 412EP AP Out Instability
Join Date: Jul 1999
Location: 58-33N. 00-18W. Peterborough UK
Posts: 3,040
Likes: 0
Received 0 Likes
on
0 Posts
412EP factory Product Data below. AHRS was standard fit from at least October 2002. Note - nearly 300 pages.
http://www.bellhelicopter.com/en/air...002_r1_web.pdf
http://www.bellhelicopter.com/en/air...002_r1_web.pdf
Perhaps the aircraft should be rendered the same standard of innocence any accused receives...."Innocent until proven guilty".
Join Date: Jul 2003
Location: UK
Posts: 461
Likes: 0
Received 0 Likes
on
0 Posts
I was the crewman on Wazz& Zoom's aircraft. Just to back him up. the a/c was AP out so there should be no inteference from the AP system. We were AP out purely for a handling exercise for the student. The vertical bounce onset almost instantly and W&Z took appropraite action for us to clear a refuel area and in the process of landing/reselcting the AP in the problem solved itself. Witnesses from an adjacent building sadi they had never seen the underside or top of the a/c in such clear view in the space of a few seconds from about 50metres.
All I could do during the event was hold on ( was on harness in the cabin) and sit in a seat. The bounce was so severe that I could not focus within the cabin, only outside and I could not release my grip to strap into the seat.
Th incident has been reported to make sure people are aware of what happened.
A similar incident occured a while ago on the same a/c where instead of vertical bounce, whilst hover taxying downwind and AP out, there were oscillations from both engines with associated oscillations of RRPM and torque fluctuations and resultant yawing. This was reported to the engineers but no incident raised at the time. Again, no fault found!
All I could do during the event was hold on ( was on harness in the cabin) and sit in a seat. The bounce was so severe that I could not focus within the cabin, only outside and I could not release my grip to strap into the seat.
Th incident has been reported to make sure people are aware of what happened.
A similar incident occured a while ago on the same a/c where instead of vertical bounce, whilst hover taxying downwind and AP out, there were oscillations from both engines with associated oscillations of RRPM and torque fluctuations and resultant yawing. This was reported to the engineers but no incident raised at the time. Again, no fault found!
It's very easy to confuse vertical bounce with rapid fore and aft movements of the cyclic - several Squirrels (AS 350) were snagged for vertical bounce when I was the MTP. They all turned out to have faulty vertical gyros which, at a particular pitch attitude, would produce this effect. Thus, I still feel the most likely reason for the situation was the stude simply overcontrolling in pitch - easy to do with both APs out on a 412 (and I still think it's a daft thing to do).
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Forget
Been down that road and unfortunately not in the cameras view.
Wazz
Probably too late but are there any local security cameras that may have this on record?
Wazz
Have ya'll called Bell to see what they have to say about it?
No doubting it happened or if it was an eye opener....just wondering what the actual cause of it is?
My hunch is something to do with Collective Friction or a bad collective bell crank or bearing.....everything all ticketyboo with the bellcranks, linkages, rod ends, collective friction setting? Any elongated bolt holes in the Bell Cranks?
If it were the friction setting....it should also show up in the AP mode or something similar.
Was the collective itself moving?
Did either pilot brace the collective with a knee so it could not move?
No doubting it happened or if it was an eye opener....just wondering what the actual cause of it is?
My hunch is something to do with Collective Friction or a bad collective bell crank or bearing.....everything all ticketyboo with the bellcranks, linkages, rod ends, collective friction setting? Any elongated bolt holes in the Bell Cranks?
If it were the friction setting....it should also show up in the AP mode or something similar.
Was the collective itself moving?
Did either pilot brace the collective with a knee so it could not move?
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
SASless
FBH have called Bell but they weren't interested; no surprise there then. If you don't pay up front then nothing will be done.
The gingerbeers checked the a/c as per the approved Bell post incident maintenance checks including the collective friction. Not sure about the bolt holes in the bell cranks though.
The collective was not moving of its own accord or being moved by me.
OldBeefer
The bounce happened after I took control.
22 Gp have now reduced the standard of AP out flying from Level 4 to 3, (For the unitiated: Level 1 crap, Level 5 Exceptional) therefore this is the only flying discipline in the Multi Engine Advanced course that is not a mandatory level 4 requirement to get the issue of RAF/RN wings! Haven't quite figured out why that is yet, and to be honest, I don't get paid enough to ask; you do as you're asked by the military commanders.
FBH have called Bell but they weren't interested; no surprise there then. If you don't pay up front then nothing will be done.
The gingerbeers checked the a/c as per the approved Bell post incident maintenance checks including the collective friction. Not sure about the bolt holes in the bell cranks though.
The collective was not moving of its own accord or being moved by me.
OldBeefer
The bounce happened after I took control.
22 Gp have now reduced the standard of AP out flying from Level 4 to 3, (For the unitiated: Level 1 crap, Level 5 Exceptional) therefore this is the only flying discipline in the Multi Engine Advanced course that is not a mandatory level 4 requirement to get the issue of RAF/RN wings! Haven't quite figured out why that is yet, and to be honest, I don't get paid enough to ask; you do as you're asked by the military commanders.
FT: As I said, 'personally' a preference, and I know quite a few others who do the same. (SAS: I prefer the Huey this way too: sorry!)
What about critical azimuth? Any thoughts?
What about critical azimuth? Any thoughts?
"FBH have called Bell but they weren't interested; no surprise there then. If you don't pay up front then nothing will be done."
A little surprised in that statement:
1) The Bell I know would jump on this and get to the root cause.
2) Last time I checked Bell doesn't charge for support.
A little surprised in that statement:
1) The Bell I know would jump on this and get to the root cause.
2) Last time I checked Bell doesn't charge for support.
Join Date: Jul 2001
Location: ...in view of the 'Southern Cross' ...
Posts: 1,383
Received 0 Likes
on
0 Posts
Mmmm ...
The company for whom I work (?) have 2 412EPs with AHRS and the 3 axis kit.
Nobody has reported anything like this on those machines in the past 8 years.
With the other 10+ (common or garden variety 412EPs) only one has reported anything like this occurrence and that was whilst carrying out an underslung operation (with both APs engaged) .... P1 still has the stains in his uniform pants, P2 reported (eyeballs uncaged rapidly) ...cause was put down to "collective bounce" don't know what engineering came up with ...
The noble quest (for information) continues ....
Good Luck
The company for whom I work (?) have 2 412EPs with AHRS and the 3 axis kit.
Nobody has reported anything like this on those machines in the past 8 years.
With the other 10+ (common or garden variety 412EPs) only one has reported anything like this occurrence and that was whilst carrying out an underslung operation (with both APs engaged) .... P1 still has the stains in his uniform pants, P2 reported (eyeballs uncaged rapidly) ...cause was put down to "collective bounce" don't know what engineering came up with ...
The noble quest (for information) continues ....
Good Luck
Well, there you are then!
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
212 & Oldbeefer.
Really constructive words and intelligently put.. not!
But if you put your head above the parapit then expect incoming....8-9-10 breathe.
Once again... the cyclic was not the root cause, IMHO it was the collective. I know what fore and aft oscillation feels like and this was not it. Quickly waggle the cyclic fore and aft a few inches and the 412 will shudder and buck about either AP in or out. We've all done this to prove a point to a student that small control movements will produce a stable hover.
Now if we had an FDR, we could analyse the data and work out if I f~+cked up or the cab is at fault.
Much like our 412 HAR2 that spun through 360 degs on initial take off a few months ago at Shawbury; everyone hear about that?? The FDR showed up exactly what caused the incident and we have all learnt from it.
I've learnt sod all from my incident except that I can't say MAYDAY when bouncing up and down like a fairground ride gone runaway and some other worldwide 412 drivers have had some scary incidents that they/engineers couldn't explain.
The quest continues.
Really constructive words and intelligently put.. not!
But if you put your head above the parapit then expect incoming....8-9-10 breathe.Once again... the cyclic was not the root cause, IMHO it was the collective. I know what fore and aft oscillation feels like and this was not it. Quickly waggle the cyclic fore and aft a few inches and the 412 will shudder and buck about either AP in or out. We've all done this to prove a point to a student that small control movements will produce a stable hover.
Now if we had an FDR, we could analyse the data and work out if I f~+cked up or the cab is at fault.
Much like our 412 HAR2 that spun through 360 degs on initial take off a few months ago at Shawbury; everyone hear about that?? The FDR showed up exactly what caused the incident and we have all learnt from it.
I've learnt sod all from my incident except that I can't say MAYDAY when bouncing up and down like a fairground ride gone runaway and some other worldwide 412 drivers have had some scary incidents that they/engineers couldn't explain.
The quest continues.
Join Date: Mar 2004
Location: U.K.
Posts: 368
Likes: 0
Received 0 Likes
on
0 Posts
Much like our 412 HAR2 that spun through 360 degs on initial take off a few months ago at Shawbury; everyone hear about that?? The FDR showed up exactly what caused the incident and we have all learnt from it.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
What was the cause then?
However it proved that the 412 can carry out a 360 deg spot turn in less than 3 seconds!!
Waz'n
Not trying to be funny but, I'm still struggling to think of a scenario that you have described (after 8 yrs of trying to fix the beast) where putting the AP back in would cure the problem if it wasn't PIO.
Wazz...
Next time something like this happens....you might try taking your hand off the collective and very firmly brace the collective with your knee so it (the collective) cannot budge...not even a smidgen. Donuts to Dog droppings the wild ride will end almost immediately. That being said....there is something not quite right about the Collective friction set up on that aircraft I bet. Get the Gingerbeers to put the manuals aside....and do what they do best (well second best) and work their way through the collective control system link by link...bolt by bolt...and look for something subtle.
In the early days of flying the Chinook....we had a similar problem caused by a weak magnetic brake on the Thrust Lever (Collective Lever in Single Rotors), and every now and then took a wild rodeo kind of ride you mention. Trying to hold the Thrust Lever with one's hand only made it worse. The only way to effectively stop the Lever from bouncing was to do as I described....use a leg to act as a physical lock and firmly hold the Lever against it until the Bounce went away...usually only one or two bounces at most.
It would be worth trying anyway.
Next time something like this happens....you might try taking your hand off the collective and very firmly brace the collective with your knee so it (the collective) cannot budge...not even a smidgen. Donuts to Dog droppings the wild ride will end almost immediately. That being said....there is something not quite right about the Collective friction set up on that aircraft I bet. Get the Gingerbeers to put the manuals aside....and do what they do best (well second best) and work their way through the collective control system link by link...bolt by bolt...and look for something subtle.
In the early days of flying the Chinook....we had a similar problem caused by a weak magnetic brake on the Thrust Lever (Collective Lever in Single Rotors), and every now and then took a wild rodeo kind of ride you mention. Trying to hold the Thrust Lever with one's hand only made it worse. The only way to effectively stop the Lever from bouncing was to do as I described....use a leg to act as a physical lock and firmly hold the Lever against it until the Bounce went away...usually only one or two bounces at most.
It would be worth trying anyway.
SaS,
with the utmost respect, I doubt if anyone has the reactions to do anything other than lower the lever After they have **** their pants with that sort of sudden occurrence!
Maybe it's my old age, but that's all I would probably manage
with over 3000 hrs on type, my only farts have been self inflicted
with the utmost respect, I doubt if anyone has the reactions to do anything other than lower the lever After they have **** their pants with that sort of sudden occurrence!
Maybe it's my old age, but that's all I would probably manage
with over 3000 hrs on type, my only farts have been self inflicted
A Blast from the past 
Here is General Operation Safety Notice 76-6:
OSN-GEN- 76-6
TO: ALL 206A/B/L, 204B, 205A1 AND 212 OPERATORS
SUBJECT: COLLECTIVE MINIMUM FRICTION
SOME OPERATORS ARE FAILING TO MAINTAIN THE REQUIRED COLLECTIVE MINIMUM FRICTION. ADJUSTMENT FOR COLLECTIVE MINIMUM FRICTION (NOT TO BE CONFUSED WITH COLLECTIVE FRICTION THAT IS AFFECTED BY ADJUSTMENT OF THE KNURLED NUT ON THE COLLECTIVE STICK) MUST BE ACCOMPLISHED ON THE GROUND BY QUALIFIED MAINTENANCE PERSONNEL AS SET FORTH IN EACH MODEL'S MAINTENANCE MANUAL*. MAINTENANCE OF COLLECTIVE MINIMUM FRICTION IS A CERTIFICATION REQUIREMENT BY THE FAA AND IS DESIGNED TO PRECLUDE "COLLECTIVE BOUNCE" BY:
1. REDUCING THE EFFECTS OF PILOT OVER-CONTROL.
2. REDUCING EFFECTS OF WIND GUSTS AND TURBULENCE THROUGH THE ROTOR INTO THE AIRFRANE.
3. PREVENTING FEEDBACK FROM EXTERNAL SLING LOADS INTO THE AIRFRAME.
IF "COLLECTIVE BOUNCE" SHOULD OCCUR WITH THE PROPER COLLECTIVE MINIMUM FRICTION, THE CAUSE MAY BE WORN LINKAGES, PILOT OVERCONTROL, EXTREME TURBULENCE OR HYDRAULIC CYLINDER IN NEED OF REWORK, WHICH SHOULD BE CORRECTED INMEDIATELY.
DO NOT FLY WITHOUT PROPER COLLECTIVE MINIMUM FRICTION.
The only reason the 412 is not listed at the top is because it wasn't invented yet (1976 versus 1980) but same logic applies.
Me agrees with SASless; collective bounce is the prime suspect
Here is General Operation Safety Notice 76-6:
OSN-GEN- 76-6
TO: ALL 206A/B/L, 204B, 205A1 AND 212 OPERATORS
SUBJECT: COLLECTIVE MINIMUM FRICTION
SOME OPERATORS ARE FAILING TO MAINTAIN THE REQUIRED COLLECTIVE MINIMUM FRICTION. ADJUSTMENT FOR COLLECTIVE MINIMUM FRICTION (NOT TO BE CONFUSED WITH COLLECTIVE FRICTION THAT IS AFFECTED BY ADJUSTMENT OF THE KNURLED NUT ON THE COLLECTIVE STICK) MUST BE ACCOMPLISHED ON THE GROUND BY QUALIFIED MAINTENANCE PERSONNEL AS SET FORTH IN EACH MODEL'S MAINTENANCE MANUAL*. MAINTENANCE OF COLLECTIVE MINIMUM FRICTION IS A CERTIFICATION REQUIREMENT BY THE FAA AND IS DESIGNED TO PRECLUDE "COLLECTIVE BOUNCE" BY:
1. REDUCING THE EFFECTS OF PILOT OVER-CONTROL.
2. REDUCING EFFECTS OF WIND GUSTS AND TURBULENCE THROUGH THE ROTOR INTO THE AIRFRANE.
3. PREVENTING FEEDBACK FROM EXTERNAL SLING LOADS INTO THE AIRFRAME.
IF "COLLECTIVE BOUNCE" SHOULD OCCUR WITH THE PROPER COLLECTIVE MINIMUM FRICTION, THE CAUSE MAY BE WORN LINKAGES, PILOT OVERCONTROL, EXTREME TURBULENCE OR HYDRAULIC CYLINDER IN NEED OF REWORK, WHICH SHOULD BE CORRECTED INMEDIATELY.
DO NOT FLY WITHOUT PROPER COLLECTIVE MINIMUM FRICTION.
The only reason the 412 is not listed at the top is because it wasn't invented yet (1976 versus 1980) but same logic applies.
Me agrees with SASless; collective bounce is the prime suspect