Bell 412EP AP Out Instability
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
In answer to the various posts:
The Right Hand Seats left hand wasn't anywhere near the collective when the bounce started (as he had relaxed by then).
The Pedestal Master Force Trim switch was on but can't vouch if during the bounce I pressed the cyclic FTR button.
We don't fly the a/c in ATT mode except on long IFR transits.
Will find the exact Honeywell AFCS Model and Mod state and post it.
Other thoughts from a senior 412 operator were:
The Heads Pendulum Dampers could possibly set up a bounce if harmonised to the ?Hz oscillation. 24lb per blade root is enough mass to create a bounce.
My thoughts were- 'but why would engaging the AP damp it out?'
Still confused but 'good ideas club' inputs are heartily welcomed.
The Right Hand Seats left hand wasn't anywhere near the collective when the bounce started (as he had relaxed by then).
The Pedestal Master Force Trim switch was on but can't vouch if during the bounce I pressed the cyclic FTR button.
We don't fly the a/c in ATT mode except on long IFR transits.
Will find the exact Honeywell AFCS Model and Mod state and post it.
Other thoughts from a senior 412 operator were:
The Heads Pendulum Dampers could possibly set up a bounce if harmonised to the ?Hz oscillation. 24lb per blade root is enough mass to create a bounce.
My thoughts were- 'but why would engaging the AP damp it out?'
Still confused but 'good ideas club' inputs are heartily welcomed.
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
Posts: 1,835
Likes: 0
Received 2 Likes
on
2 Posts
wazz:
Why not fly it in ATT mode all the time? Learn to get used to the control forces and fly through it without using the force trim release all the time.
While it's not the greatest AFCS in the world, it's not bad, and when you get used to it, it actually does reduce workload, even in the hover.
Why not fly it in ATT mode all the time? Learn to get used to the control forces and fly through it without using the force trim release all the time.
While it's not the greatest AFCS in the world, it's not bad, and when you get used to it, it actually does reduce workload, even in the hover.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Hi Shawn
Our 'customer' requires their student's to able to operate the aircraft VFR and IFR by Day, Night and NVG using SAS mode not via the luxury mode of ATT. Procedural transits can utilise the ATT mode but approaches are done in SAS mode.
With only the 3 axis system fitted however, it is only an area weapon. The 4 axis AP with full SAR mode is a lovely bit of kit though.
Our 'customer' requires their student's to able to operate the aircraft VFR and IFR by Day, Night and NVG using SAS mode not via the luxury mode of ATT. Procedural transits can utilise the ATT mode but approaches are done in SAS mode.
With only the 3 axis system fitted however, it is only an area weapon. The 4 axis AP with full SAR mode is a lovely bit of kit though.
Last edited by wazz'n'zoom; 13th Jun 2010 at 14:04.
Sounds like the customer is mixing coupled modes with basic AFCS modes! I agree with Shawn - press the FTR button to yank and bank, release it when you don't need to!
RFM Page 1-11, Limitations, AFCS shall be operated in ATT mode during IFR flight.
We experimented plenty with ATT and SAS. Most time we left it in ATT and used the FTR to move it around. Nothing "luxury" about it, just how the helicopter flies best. First I've heard of anyone wanting to keep it in SAS. I'd be interested to hear the reason.
We experimented plenty with ATT and SAS. Most time we left it in ATT and used the FTR to move it around. Nothing "luxury" about it, just how the helicopter flies best. First I've heard of anyone wanting to keep it in SAS. I'd be interested to hear the reason.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Malabo
The 412s here are not operated 'fully' via the Bell RFM but by a 'MOD Military Release to Service'. This works in conjunction with the RFM but has several over-riding differences which, have been cleared by Bell.
The service does not want their student pilots using the ATT mode, as it is too automated and easy to fly but therefore prefer to use SAS mode for a more 'manual flight' mode therefore testing the student more. Thus, only the Honeywell SPZ-7600 3 axis AFCS was selected during the purchase of the aircraft in 1997.
When 2 extra 412EPs were purchased 10yrs ago, the a/c arrived with AHRS instead of TARSYNS. This is one of the a/c that had the 'Vertical Bounce' and some other 'odd' handling issues.
The service are requesting an inquiry into this area so that a student pilot does not suffer the same, potentially serious 'AP out' incident.
The 412s here are not operated 'fully' via the Bell RFM but by a 'MOD Military Release to Service'. This works in conjunction with the RFM but has several over-riding differences which, have been cleared by Bell.
The service does not want their student pilots using the ATT mode, as it is too automated and easy to fly but therefore prefer to use SAS mode for a more 'manual flight' mode therefore testing the student more. Thus, only the Honeywell SPZ-7600 3 axis AFCS was selected during the purchase of the aircraft in 1997.
When 2 extra 412EPs were purchased 10yrs ago, the a/c arrived with AHRS instead of TARSYNS. This is one of the a/c that had the 'Vertical Bounce' and some other 'odd' handling issues.
The service are requesting an inquiry into this area so that a student pilot does not suffer the same, potentially serious 'AP out' incident.
Last edited by wazz'n'zoom; 13th Jun 2010 at 14:05.
I tend to agree with Old Beefer and the other poster who correctly stated that a high frequency pitch oscillation can be misinterpreted as a vertical bounce. The Bell 212 with the basic SCAS sometimes suffered from a 'chattering' pitch gyro (loose wires) which would induce a severe vibration, as have other types (AS332 sometimes prone.) But, if the AP was 'out' in the first place then there should be no interaction at all with the controls from the AFCS. Reference to the collective channel is a red hering I think, because even where it to be functional, it would only be a trim actuator, and not a a SAS actuator, so would be unable to generate the frequency you describe.
You should not be surprised at how quickly the AP killed the problem. The disc is typically moved by the SAS far more rapidly than any pilot inputs and the fact it only has 10%, or so, authority is misleading too - try moving the cyclic back and to within 10% of it's range and see what the aircraft does!
I strongly suspect that there is something unrelated to the specific AFCS which has led to a PIO, and because it happens to be a unique AFCS fit within the fleet that is disracting your attenton.
I'm sure we will all be very interested to know the final outcome
PS. As FBH machines, do they have CVFDRs fited, or HUMS? I'm sure there will be some clues in their recordings.
You should not be surprised at how quickly the AP killed the problem. The disc is typically moved by the SAS far more rapidly than any pilot inputs and the fact it only has 10%, or so, authority is misleading too - try moving the cyclic back and to within 10% of it's range and see what the aircraft does!
I strongly suspect that there is something unrelated to the specific AFCS which has led to a PIO, and because it happens to be a unique AFCS fit within the fleet that is disracting your attenton.
I'm sure we will all be very interested to know the final outcome
PS. As FBH machines, do they have CVFDRs fited, or HUMS? I'm sure there will be some clues in their recordings.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
212man
Interesting observations.
FBH did not send the CVR off to be read (it was impounded pending an inquiry but has since been re-used therefore overwriting the data
) and the a/c is not fitted with FDR (both deemed too expensive).
Quote: I strongly suspect that there is something unrelated to the specific AFCS which has led to a PIO, and because it happens to be a unique AFCS fit.
It's a shame the other pilots on the unit have not reported the 'other instances' relating to the 'odd handling issues' apertaining to only 2 of our 412EP's (both 3 axis AHRS). If i had a quid for every time someone has said "Oh i had something similar to that the other week/month" It'd pay for a few rounds at the local. As it is, most of us are unwilling to disengage the AP on these 2 AHRS a/c.
When my next delivery of 'brave pills' arrive, I'll go up with the test pilot and show him what led to the incident.
Watch this space!
Interesting observations.
FBH did not send the CVR off to be read (it was impounded pending an inquiry but has since been re-used therefore overwriting the data
) and the a/c is not fitted with FDR (both deemed too expensive).Quote: I strongly suspect that there is something unrelated to the specific AFCS which has led to a PIO, and because it happens to be a unique AFCS fit.
It's a shame the other pilots on the unit have not reported the 'other instances' relating to the 'odd handling issues' apertaining to only 2 of our 412EP's (both 3 axis AHRS). If i had a quid for every time someone has said "Oh i had something similar to that the other week/month" It'd pay for a few rounds at the local. As it is, most of us are unwilling to disengage the AP on these 2 AHRS a/c.
When my next delivery of 'brave pills' arrive, I'll go up with the test pilot and show him what led to the incident.
Watch this space!
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
Posts: 1,835
Likes: 0
Received 2 Likes
on
2 Posts
Anytime something out of the ordinary happens to an AFCS, it should be reported!!!
Tell the folks who don't report things officially, but tell you after over a pint that how would they like it if a really serious problem didn't get report and was still present when they got the aircraft?
In fact, any time something out of the ordinary happens to a system it should be reported somewhere, somehow. A Bell 212 crashed with a total electrical failure (which is not supposed to ever be able to happen to it) and it was discovered that not only had that airframe had a total electrical failure a year before, but there was at least one other airframe that had a similar problem - neither got reported. 7 dead.
Tell the folks who don't report things officially, but tell you after over a pint that how would they like it if a really serious problem didn't get report and was still present when they got the aircraft?
In fact, any time something out of the ordinary happens to a system it should be reported somewhere, somehow. A Bell 212 crashed with a total electrical failure (which is not supposed to ever be able to happen to it) and it was discovered that not only had that airframe had a total electrical failure a year before, but there was at least one other airframe that had a similar problem - neither got reported. 7 dead.
Sorry to be pedantic, but I understand that the aircraft was check flown after the incident by 2 'real' (ie graduate) test pilots, who, like the engineers, were unable to find a fault with the aircraft.
It's quite easy to get 'in the loop' with the 412 in AP-out spot turns, but I had not heard of a vertical PIO. I wonder whether it started out as a bit of roll oscillation, which excited some yaw, and then coupled with a bit of heave, which got out of hand? Only 3-axis Helipilot, methinks, so can't blame the collective channel. And I gather that re-engaging the AP stopped it all.
Lesson: Don't taxy in AP out (especially with a tailwind..and NB critical azimuth..?) when you're about to RRF. There's a time and a place for practising what should be a 'degraded mode'.
Ah: the Force Trim! Another old chestnut. Personally, in high-gain situations, either 212/412: FT OFF. That means, basically, below about 250 ft. Above that, FT ON. Then ATT mode as soon as possible. Philosophy: use the FT and Helipilot system as it was designed to be used on the type in question, not because that's how another type's is used when you pop out of the flying training empire.
It's quite easy to get 'in the loop' with the 412 in AP-out spot turns, but I had not heard of a vertical PIO. I wonder whether it started out as a bit of roll oscillation, which excited some yaw, and then coupled with a bit of heave, which got out of hand? Only 3-axis Helipilot, methinks, so can't blame the collective channel. And I gather that re-engaging the AP stopped it all.
Lesson: Don't taxy in AP out (especially with a tailwind..and NB critical azimuth..?) when you're about to RRF. There's a time and a place for practising what should be a 'degraded mode'.
Ah: the Force Trim! Another old chestnut. Personally, in high-gain situations, either 212/412: FT OFF. That means, basically, below about 250 ft. Above that, FT ON. Then ATT mode as soon as possible. Philosophy: use the FT and Helipilot system as it was designed to be used on the type in question, not because that's how another type's is used when you pop out of the flying training empire.
As I did not attend the vaunted CFS, and thus am not qualified to say anything about helicopter flying despite having done a life time of it....I will risk inciting riot and barbed responses by saying this.
I was taught to use "attitude" to hover and fly a helicopter. That being....select the attitude that provides the desired results....be it a steady hover or a rate of turn or airspeed or whatever. It was always about "attitude" and "sight picture". When I progressed to larger and more complex helicopters the basics did not change... just the way one went about it.
So....I ask you....if the helicopter has an "ATT" mode....and it functions with the FT "ON".....why not use it to "hold" the attitude you select by moving the cyclic stick? I might be awfully wrong but my memory of every single helicopter I ever flew....either manually moving the cyclic or selecting the FT "Off" by either switching it off or mashing the FT button on the cyclic allowed one to revert to "SAS" mode or override the autopilot.
Even in the venerable Huey one could use friction and FT to provide steadier hover and flight with a reduced work load on the pilot.
For training purposes....using reduced modes of autopilot/stability systems is good practice but should not be suggested as "The" way to fly the aircraft in normal operations.
The quickest way to get a Huey bouncing vertically (other than Engineering) is by moving the cyclic fore and aft in a fairly rapid cycle. Tranny mounts and Lift Link bearings are another way if not checked properly or replaced when worn. The 212/412 is no different in that regard.
I was taught to use "attitude" to hover and fly a helicopter. That being....select the attitude that provides the desired results....be it a steady hover or a rate of turn or airspeed or whatever. It was always about "attitude" and "sight picture". When I progressed to larger and more complex helicopters the basics did not change... just the way one went about it.
So....I ask you....if the helicopter has an "ATT" mode....and it functions with the FT "ON".....why not use it to "hold" the attitude you select by moving the cyclic stick? I might be awfully wrong but my memory of every single helicopter I ever flew....either manually moving the cyclic or selecting the FT "Off" by either switching it off or mashing the FT button on the cyclic allowed one to revert to "SAS" mode or override the autopilot.
Even in the venerable Huey one could use friction and FT to provide steadier hover and flight with a reduced work load on the pilot.
For training purposes....using reduced modes of autopilot/stability systems is good practice but should not be suggested as "The" way to fly the aircraft in normal operations.
The quickest way to get a Huey bouncing vertically (other than Engineering) is by moving the cyclic fore and aft in a fairly rapid cycle. Tranny mounts and Lift Link bearings are another way if not checked properly or replaced when worn. The 212/412 is no different in that regard.
SAS beat me to it. In my limited exposure to the 212 (5 years and 2800 hours) I never found a need to turn off the trim. I flew plenty of 'high gain' manouevres - believe me, I did - and the use of the FTR was intuitive and seamless.
212man.....someone will come along with his pocket full of colored pencils and explain exactly how wrong we are on this. We seem to have embraced the KISS method of helicopter flying....that being "Keep It Simple Stupid!" which surely confuses heck out of CFS indoctrinated folks. The mere thought of using such a dangerous device as an "Attitude Hold" feature within 500 feet of the ground must strike fear into the Checklist Readers that lurk around this place.
Yet....the very same bunch will happily let a Sea King do so in a hover at night over a Sonar Pinger.
Yet....the very same bunch will happily let a Sea King do so in a hover at night over a Sonar Pinger.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Guy's/Gal's
Let's not lose focus here and stop going down the 'force trim' rabbit hole.
Whether as some say 'You messed up' AP out, the fact remains that the a/c did something that no other helicopter I've flown has ever done....Taken control from me in a stable hover with virtually no wind!! Should that happen?...A big fat No!
It's a £2 million bit of kit that has some quirky handling and, via this forum, will stop someone else suffering the same incident. Nuff said??
p.s. Hopefully, if he is available, we should have the ex-ETPS in-flight test report/feed back next week. Wait out.
Let's not lose focus here and stop going down the 'force trim' rabbit hole.
Whether as some say 'You messed up' AP out, the fact remains that the a/c did something that no other helicopter I've flown has ever done....Taken control from me in a stable hover with virtually no wind!! Should that happen?...A big fat No!
It's a £2 million bit of kit that has some quirky handling and, via this forum, will stop someone else suffering the same incident. Nuff said??
p.s. Hopefully, if he is available, we should have the ex-ETPS in-flight test report/feed back next week. Wait out.
Last edited by wazz'n'zoom; 11th Jun 2010 at 22:21.
Join Date: May 2010
Location: Denver
Age: 54
Posts: 17
Likes: 0
Received 0 Likes
on
0 Posts
I am still amazed at the amount of people who will not engage the force trim on a 412 to this day. First thing on pre-takeoff check is "Force Trim Off' and the first thing on the after landing check is "Force Trim - On". Noticing the same thing now that I am getting into the 214ST as well.
in high-gain situations, either 212/412: FT OFF. That means, basically, below about 250 ft. Above that, FT ON. Then ATT mode as soon as possible.
One must note the difference from ATT Mode to SAS Mode is but a cyclic button click or click and hold away. Chinook pilots are well aware of this as real Chinook Pilots have a well formed callus on their right thumb....just as I did when flying 204/205/212 and 412's. I also used Cyclic friction on the non-SAS'd 204,205,212's I flew.
Now the Sixty-Four Dollara Question has been asked!
No Engineering fault found.
No Test Pilot, Test Flight reproduced the fault.
We have a Pilot who says he got quite a fright out of an unusually strong uncommanded reaction from an aircraft.
No one else has come out to say they have had anything remotely similar happen.
Pilots with thousands of hours in the same type aircraft have not reported any similar violent events in the particular aircraft or similar models.
No one has said the involved crew "cocked it up" but some have suggested PIO as a probable cause.
We all are interested in the answer for a multitude of reasons....some out of sheer boredom, some for technical reasons, and some for flying that particular aircraft or similar models.
One thing is sure....we are back asking the same question...."What Happened?"
Join Date: Dec 2001
Location: Philadelphia PA
Age: 73
Posts: 1,835
Likes: 0
Received 2 Likes
on
2 Posts
And they wonder why a FDR would be a good idea.
Not only are they very useful for incidents like this, and accidents, but they are also incredibly valuable if you're monitoring a fleet.
Sigh.
Not only are they very useful for incidents like this, and accidents, but they are also incredibly valuable if you're monitoring a fleet.
Sigh.
Thread Starter
Join Date: Jun 2007
Location: Northern Hemisphere
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
And the question still remains.. does anyone out there operate the 412EP with the Honeywell SPZ-7600 3 axis AFCS with AHRS or is it just our 2 FBH 412EPs? Have Bell sold us a lemon??
Ask about fellas/lasses.
Ask about fellas/lasses.
Join Date: Apr 2008
Location: At home
Posts: 18
Likes: 0
Received 0 Likes
on
0 Posts
We need to steer clear of tying AHRS to an AP out incident, if I remember correctly neither tarsyns or AHRs can influence the aircraft flight path if the AP is not engaged other than through the instrument-eye-hand-control route.
In SAS the ap will only be able to 'push' against the pilots stick position and therefore will always have a changing reference point, if there is control input being put in by the pilot the end effect on the flight path/attitude being unpredictable.
I believe that the mode of operation on this operation is not to use transparent piloting and either have force trim off or the button pressed. If so I seem to remember that pressing the button not only removes the 'fixed' reference point but also centres the AFCS actuators (check the API).
As ever awaiting the incoming!
In SAS the ap will only be able to 'push' against the pilots stick position and therefore will always have a changing reference point, if there is control input being put in by the pilot the end effect on the flight path/attitude being unpredictable.
I believe that the mode of operation on this operation is not to use transparent piloting and either have force trim off or the button pressed. If so I seem to remember that pressing the button not only removes the 'fixed' reference point but also centres the AFCS actuators (check the API).
As ever awaiting the incoming!