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Helicopter missing in the Med

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Helicopter missing in the Med

Old 8th Jul 2020, 21:39
  #141 (permalink)  
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Originally Posted by JohnDixson
If that is correct, then CTR is proposing ( I think? ) that everyone else is bound by a Special Condition agreed upon by Bell and the FAA, but no one else, that is not yet published as 14 CFR Part 29 and therefore is not law?
John,

Could you please rephrase your question? After reading it, I felt like I was in a “Who’s on first” Abbott and Costello routine. ;-)

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Old 8th Jul 2020, 22:14
  #142 (permalink)  
 
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My response was indeed to dispel your attempt to link lack of active control margin feedback to the accident. It is important for current operators of that aircraft to know there is more than adequate control margin throughout the operational flight envelope.

For those not familiar with the term, “unique trim” refers to a controller which resembles a joy stick. When relaxed, it is spring/detent centered. Inputs move away from the center detent by a small displacement, typically one to three inches.

Now to your other comments. I was a presenter at the early certification meetings to educate the FAA as to the Sikorsky FBW approach. There is nothing in the FARs that would prevent implementation of a unique trim controller. The main issues with the non-traditional controller approach were in demonstration of FARs such as longitudinal static stability. With automatic trim follow up (a fundamental element of unique trim), the stick is always in the same position regardless of trimmed speed. So we came up with an alternate method to demonstrate stability.

If Bell decided against a unique trim approach, that was their decision based on an assessment of the effort required to meet the certification challenges, not an FAA mandate. BTW, all the publicly accessible photos of the 525 cockpit show a sidestick with very little space for proportional control movement, at least with acceptable sensitivity. Makes one wonder, if it isn’t unique trim, what is it?

There are indeed benefits and challenges to the unique trim approach, and I have presented a couple of papers on the subject. The challenges, however, do not generally have to be mitigated by incorporation of active feedback. The control strategy with a unique trim stick is quite different than a proportional controller. If you look at time histories of a flight with a unique trim stick, you’ll notice the stick is in detent about 80% of the time. The stick moves in and out of detent at a relatively high frequency. Thus requiring the non-flying stick mirror the movement of the flying pilot is of questionable value.

Autopilot feedback? Think about what happens when you are coupled to a flight director airspeed and drag off speed with stick input. When you release the stick, do you respond to the subsequent pitch movement because the stick is moving forward or the nose is pitching down? I suggest it’s the latter.

I have considerable time in experimental helicopters with both active and passive unique trim sticks and, comparing the two, I didn’t find the active stick to provide a demonstrable improvement. And there are some nasty failure modes embedded in the active stick architecture that need to be addressed in emergency procedures.

Lastly, your contention the USMC “demanded installation of active BAE cyclics sticks” is false. Sikorsky convinced the Marines that there was potential in the active stick to incorporate tactile cueing, and if they didn’t invest in the technology now they might not be able to retrofit it later. The aircraft could handle the approximately 30 lbs weight penalty and the cost was just lost in the scope of the entire program. They are unique trim sticks and do not “mimic” the functions of mechanical controls.
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Old 9th Jul 2020, 00:14
  #143 (permalink)  
 
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CTR-sorry-it was a longer,involved sentence:

“Provokes a question. The 525 certification process was via " Special Conditions ", I think, as Part 29 and the attendant Advisory Circular do not yet address the totality of the FBW implications.If that is correct, then CTR is proposing ( I think? ) that everyone else is bound by a Special Condition agreed upon by Bell and the FAA, but no one else, that is not yet published as 14 CFR Part 29 and therefore is not law?”

The point I was getting at was:

1. The FAA told Bell they would not approve a unique trim cyclic.
2. Therefore Bell did not provide one.
3. The clear implication was that a unique trim cyclic wasn’’t certifiable, i.e., if Bell couldn’t do it neither could anyone else.
4. But remember, this is a Special Condition applying to the 525.

5. Bell’s Special Conditions are not in 14 CFR Part 29, thus are not law as far as say Boeing or Sikorsky proposing a unique trim controller.
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Old 9th Jul 2020, 13:14
  #144 (permalink)  
 
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CTR, allow me to go further. In thinking about my response above I can see where it might be misinterpreted.

The Bell folks certainly have had meaningful experience with FBW technology. When the FAA advised them that they wouldn’t be certifying a unique trim controller, Bell could very well have responded ( if they so desired to ) that they were wrong about that and proceeded to explain why, and how their system would answer all the safety and human factors considerations etc. They have the experienced and knowledgeable engineering talent to back that up whereas in the rotary wing/vertical lift area, the FAA apparently does not. I write “ apparently “ advisedly, because if they did, three decades after FBW appeared in vertical lift, they would have amended the relevant certification requirements and qualification procedures, and they have not.
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Old 10th Jul 2020, 22:27
  #145 (permalink)  
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Response to RVGuy’s Comments

RVGuy,

Immediately responding properly to your extensive comments required time I did not have. I finally have some free time. Sorry for the delay.

To try and maintain clarity and continuity in my response, I have pasted in multiple sections of your postings in quotes.

“My response was indeed to dispel your attempt to link lack of active control margin feedback to the accident. It is important for current operators of that aircraft to know there is more than adequate control margin throughout the operational flight envelope.”

Please re-read my posts. I specifically state I am not attempting to tie unique trim cyclic to the cause of this accident.

“Now to your other comments. I was a presenter at the early certification meetings to educate the FAA as to the Sikorsky FBW approach. There is nothing in the FARs that would prevent implementation of a unique trim controller. The main issues with the non-traditional controller approach were in demonstration of FARs such as longitudinal static stability. With automatic trim follow up (a fundamental element of unique trim), the stick is always in the same position regardless of trimmed speed. So we came up with an alternate method to demonstrate stability.”

Prior to your discussions with the SW FAA Office to certify the S92FBW, I was working with the same FAA personnel on the certification of the FBW flight control system for the Leonardo 609.

Just prior to Sikorsky giving up obtaining FAA certification for the S92FBW, I was involved with developing the certificate basis for FBW system on the 525. By an interesting chain of events, in between working on both of these programs I turned down an offer from Sikorsky to work on the certification of the S92FBW. So while I do not question any of your statements validity, I believe they are based on your impressions with relatively brief meetings with the FAA. My statements are based on the sum total of over 20 years working to civil certify FBW rotorcraft. I have the mental scars to prove it ;-).

You are correct there is nothing in the FARs that specifically prevents the use of unique trim cyclics. But then again, there is next to nothing in the FARs for Part 29 aircraft regarding Fly by Wire. As you well know, the FARs are vague, and their interpretation is up to the discretion of the FAA. Recently, I have witnessed two identical Issue Papers submitted to the FAA for approval on FBW issues. The one that was sent to the NY office was approved, the one that went to the SW office was turned down.

RVGuy, you may have walked away from meetings with the FAA thinking that they had accepted unique trim as being acceptable for certification. However, prior to the 525 program we specifically asked the SW FAA if unique trim would be acceptable for Part 29 (without mentioning the S92FBW), and were told no. This is not secondhand, I asked the question myself.

“If Bell decided against a unique trim approach, that was their decision based on an assessment of the effort required to meet the certification challenges, not an FAA mandate. BTW, all the publicly accessible photos of the 525 cockpit show a sidestick with very little space for proportional control movement, at least with acceptable sensitivity. Makes one wonder, if it isn’t unique trim, what is it?”

While neither the 609 or 525 are yet FAA certified, they are both are much closer to achieving this milestone than the S92FBW ever got. This is not to say that unique trim is inadequate. But it has limitations, especially when transitioning pilots familiar with conventional mechanical controls.

You need to get the opportunity to sit in a 525 mock up or aircraft. You’ll be surprised at how much displacement the cyclic actually has. It was modeled initially on the Zulu Cobra side stick displacement. The Z is all mechanical with SCAS. With all that linkage and resulting lost motion, a very short stick would’ve resulted in an unacceptable dead band. So yes, the 525 mimics conventional mechanical controls, with proportional movement. This is best displayed on aircraft start up. Prior to rotors turning the 525 does not have hydraulic pressure to the swashplate actuators. Therefore, upon start up the cyclic stick moves to synchronize up with the swashplate position. The same goes for the 609.

As I mentioned before, the biggest concern with dual control unique trim the FAA expressed was with pilot to copilot coordination. When the FAA was asked why unique trim was acceptable on large commercial airliners but not for helicopters, pilot to copilot coordination when operating close to obstacles was the first concern. This is why although the 525 has side sticks, the two-sided sticks are mechanically linked.

Thanks to Nick Lappos’s brief stay at Bell, the 525 incorporates some advanced control features similar to what he pushed for on the S92FBW. But the FAA moves very slowly and excepting new technology. So many of the original features had to be stripped out in order to achieve certification. But it’s now only a software update to bring them back.

“There are indeed benefits and challenges to the unique trim approach, and I have presented a couple of papers on the subject. The challenges, however, do not generally have to be mitigated by incorporation of active feedback. The control strategy with a unique trim stick is quite different than a proportional controller. If you look at time histories of a flight with a unique trim stick, you’ll notice the stick is in detent about 80% of the time. The stick moves in and out of detent at a relatively high frequency. Thus requiring the non-flying stick mirror the movement of the flying pilot is of questionable value.

“I have considerable time in experimental helicopters with both active and passive unique trim sticks and, comparing the two, I didn’t find the active stick to provide a demonstrable improvement. And there are some nasty failure modes embedded in the active stick architecture that need to be addressed in emergency procedures.”

I agree concerning the potential nasty failure modes with many active stick architecture’s. This is especially a concern with dual controls, where force feel must also replicate pilot to copilot interaction. This is another reason why the 525 cyclics are mechanically linked. The single actuator that provides force feel for each axis can be kept to a very low load and rate, similar to conventional mechanical controls.

“Lastly, your contention the USMC “demanded installation of active BAE cyclics sticks” is false. Sikorsky convinced the Marines that there was potential in the active stick to incorporate tactile cueing, and if they didn’t invest in the technology now they might not be able to retrofit it later. The aircraft could handle the approximately 30 lbs weight penalty and the cost was just lost in the scope of the entire program. They are unique trim sticks and do not “mimic” the functions of mechanical controls.”

I had the opportunity to visit be BAE and get a demonstration of an earlier generation of the CH 53K active sticks. Additionally, I presented a paper at the SAE A6 conference, when NAVAIR present a paper on the CH-53K active sticks. My statement was based on what I was stated by both BAE and NAVAIR representatives. Also if you reread my statement you will see that I stated that active sticks were incorporated so that the cyclic controls ‘COULD’ mimic conventional mechanical controls, not would mimic. As was the case with the 525 certification, being able to mimic conventional mechanical controls reduced potential program risk.

Finally, I believe you were being kind by saying it was only a 30 lb hit in weight For active sticks on the CH 53K. For both cyclics and associated electronics, I believe it’s more than twice that amount.

Stay healthy,

CTR

PS John Dixon, I will respond to your posting as soon as I get some more time.

Last edited by CTR; 12th Jul 2020 at 20:27.
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Old 11th Jul 2020, 13:35
  #146 (permalink)  
 
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Good post, and I look forward to the response from the RVguy. You two are clearing the air a bit re FBW, and there was one issue touched on that has been a problem to me for decades-the “out of dateness“ of the longitudinal static stability requirement.

The idea behind the requirement sounds fine: it should require forward control input to go faster and vice versa. The associated “ stability “ part-that the stick position vs speed must show a positive/negative slope sounds fine, until one thinks about it. The assumption is that if the pilot doesn’t move the control, the aircraft will stay right there, on speed. Its stable..All is well. The reality is that when a change in speed is demanded, the control is moved forward ( for example ) then as the ship gets to the desired speed, the pilot makes the adjustments to stop the acceleration and fine trim the ship to the new speed. Its “ nice” if that measured position is forward of the original, but what matters is if the ship stays there.

In the modern fleets of machines there are some that stand out as having to add equipment ( sensors, actuators etc ) to meet the positive stick position slope: the CH-47 series, the UH-60, the S-76 and the 53E. DASH, Pitch Bias Actuators ( PBA ) etc. The UH-60 case stands out in my mind. There was a speed area at max aft CG where the stick position measurement in smooth air etc was flat to slightly negative. We had to add all the claptrap associated with the PBA. We tried to reason with the Army that the pilot would never know the difference ( if he didn’t have the PBA )because the AFCS had airspeed hold automatically locking on after 12 seconds ( i.e., the ship would stay where the pilot put it, speed wise ). Lost that argument. Scene shifts forward 3-4 years and the PBA subsystem was a frequent cause of maintenance actions. Had another meeting with the Army, who now knew that the pilots couldn’t determine any change in the handling and the PBA was removed.

My point is that if the aircraft stays where the pilot trims it, the stick position slope argument with modern control systems is baseless-the modern control system solves the original intent with modern technology. Solution on the other side of the discussion is to modernize the regulations.

Last edited by JohnDixson; 11th Jul 2020 at 13:38. Reason: typo/added thought
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Old 21st Oct 2020, 05:05
  #147 (permalink)  
 
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CTR - Check your PMs please

Grizz
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Old 21st Oct 2020, 18:23
  #148 (permalink)  
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Originally Posted by grizzled
CTR - Check your PMs please

Grizz
Grizz,

See response.

Stay healthy,

CTR
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Old 25th Jun 2021, 21:05
  #149 (permalink)  
 
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https://atlantic.ctvnews.ca/canadian...2020-1.5485958

Canadian Forces pilots not warned about autopilot before deadly Cyclone crash in 2020
By Michael TuttonThe Canadian Press Staff

Contact

Published Friday, June 25, 2021 4:34PM ADT Last Updated Friday, June 25, 2021 4:40PM ADT

From top left: Sub-Lieutenant Abbigail Cowbrough, a Marine Systems Engineering Officer; Sub-Lieutenant Matthew Pyke, Naval Warfare Officer; Master Corporal Matthew Cousins, Airborne Electronic Sensor Operator; Captain Maxime Miron-Morin, Air Combat Systems Officer; Captain Kevin Hagen, Pilot; Captain Brenden Ian MacDonald, Pilot.
HALIFAX -- As a pilot guided one of Canada's navy helicopters up into a tight turn, neither his training nor cockpit indicators warned of how a built-in autopilot would take control and plunge the Cyclone into the Ionian Sea, a military report has concluded.

All six Canadian Forces members on board died in the crash on April 29, 2020.

According to a board of inquiry report obtained by The Canadian Press, when the pilot was flying the turn, commonly called a "return to target," he had pointed the nose up and used his feet to turn the helicopter's tail, overriding the autopilot to complete the manoeuvre of less than 20 seconds.

The report, however, said testing wasn't done during the aircraft's certification to identify what would happen if a pilot overrode the autopilot more than "momentarily" and in certain complex situations. "The automation principles and philosophy that governed the Cyclone's design never intended for the (autopilot) to be overridden for extended periods of time, and therefore this was never tested," it said.

This was the case even though -- as the report stated -- pilots are known on occasion to override the autopilot system without manually pressing a button on their control stick, called the cyclic.

The report said that at the time of the crash, the autopilot -- referred to as the flight director -- was set to an air speed of about 260 kilometres per hour before one of the pilots pitched the aircraft's nose upward for the turn.

It was supposed to fly back over HMCS Fredericton and practice hoisting people onto the deck. Instead, the frigate's CH-148 Cyclone helicopter crashed off the coast of Greece while returning from a NATO training mission. That crash caused the worst single-day loss of life for the Canadian Armed Forces since six soldiers were killed in a roadside bombing in Afghanistan on July 4, 2007.

The report indicated the crash might have been averted if the pilot had manually chosen to turn off the autopilot during the turn. But it also stated that it wasn't unusual for pilots to override the autopilot and there were no explicit instructions in the manuals on the necessity to manually turn off the flight director.

In addition, the report said the pilot appeared unaware the computer would attempt to regain control near the end of the turn.

When the helicopter flipped around, the report said, the pilot pulled back as far as he could on the cyclic, attempting to right the aircraft that the computer was flying into the sea. Within seconds, the helicopter hit the ocean at massive force.

The board of inquiry said it found no evidence the flying pilot recognized he had lost control of the aircraft until it was too late.

Critical to the crash, the report said, was the aircraft's software, which was certified by the military. If the autopilot is overridden, the computer accumulates digital commands, referred to as "command bias accumulation." The more commands a pilot sends manually to the computer while the aircraft is coupled with the autopilot, the more this bias accumulation occurs, the report said.

'PILOT'S ABILITY TO CONTROL AIRCRAFT WILL BE REDUCED OR LOST'

After a pilot overrides the air speed set by the autopilot, a "feed forward look" occurs, the report said, adding that in some situations, "the pilot's ability to control the aircraft will be reduced or lost."

The board of inquiry said the pilots' training didn't cover "with sufficient detail" certain risks of flying the aircraft, leaving the flyers unaware the autopilot would seek to keep control of the helicopter.

The return-to-target manoeuvre, which led to the crash, was being flown by others in the maritime helicopter community, the report said. That manoeuvre has been disallowed since the crash.

The report makes six recommendations, five of which involve better training for pilots to make them aware of the potential problems that could occur if they override the autopilot. It recommended creating special cockpit signals pilots could use to warn each other about overriding flight directors for extended periods of time.

The report also recommended the military consider an engineering change "to automatically disengage the flight director under certain conditions, such as when the flight director is overridden in multiple axes, or for an extended period of time."

According to a senior military source, that recommendation is not shared in a second, independent report by the military's Directorate of Flight Safety, expected to be released next week.

The second report said pilots must be well trained to almost instantly press a single button on their control stick to disengage the autopilot if they're not getting the response they want out of their controls. It said, however, that automatically disengaging the autopilot might pose its own risks in some situations, especially when a pilot believes the autopilot will keep functioning.

The second report instead argued that the software -- and its "bias accumulation" -- needs to be addressed by American aviation company Sikorsky Aircraft, the manufacturer of the Cyclone.



"We need to look at that software and see if we can eliminate this from the software altogether, being careful to understand when you make any changes like that you may introduce a butterfly effect and cause problems elsewhere," the source said.

The board of inquiry report, signed by three members of the panel on Nov. 20, 2020, concluded the pilots were not distracted and the crew "flew well together." It added that the aircraft captain had a strong command of the helicopter and the co-pilot showed "good situational awareness" throughout the mission.

The second report is expected to provide further analysis on the factors behind the crash.

The military source said the recommendations of the two reports must be meshed into a single set of findings for consideration by senior Royal Canadian Air Force officers.

A spokeswoman for Sikorsky referred all questions on the report to the Canadian Forces.

This report by The Canadian Press was first published June 25, 2021.
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