Bell 429 - undemanded yaw question

[HeliHenri]

.
https://www.verticalmag.com/press-re...otor-incident/
You are reassured now ?
.

[SASless]

Seems a Two Bit Explanation to me!

[[email protected]]

Perhaps a public acknowledgement by Mr Philpott of the pilots skill in preventing what could easily have been a catastrophe would have been nice.

[SASless]

It would be nice to know what actually caused the problem and what the bits were that were replaced.....and what kind of testing they did to sort out the issues.

Also....it wasn't just a bit of yawing but was two and half full rotations.....which would have been a very interesting ride!

Very good of the pilot to keep the aircraft upright on keep it from rolling over.

[Dai Whirlybird]

So the press release includes " the manufacturer recommended the precautionary replacement of two components"

That seems to me to equate to "system tested no fault found." I interpret that as the two components have been found by the manufacturer NOT to be demonstrating any obvious sign of malfunction or failure but have been replaced as a "precautionary" measure. Whilst I applaud any measure taken in the name of safety. just in case or otherwise, it's hardly a definitive conclusion.

I just hope and pray that the potential for a catastrophic technical failure has been removed by these measures, but at the risk of sounding disloyal to a fellow pilot and introducing the elephant in the room, the possibility of pilot error hasn't been mentioned. After all we are known to be fallible.

The authorities are clearly satisfied and have released the airframe back into service so it can now continue to deliver medical aid to Wiltshire which has to be a positive, but the cause has yet to be either identified or as I (cynically) suspect it is known, but yet to be promulgated.

[booke23]

Having read the latest statement, I'm a bit surprised the AAIB haven't got involved.

It seems to have been a "serious incident involving a commercial aircraft" .......this would normally warrant an AAIB correspondence investigation.

[Dai Whirlybird]

Originally Posted by booke23

Having read the latest statement, I'm a bit surprised the AAIB haven't got involved.

It seems to have been a "serious incident involving a commercial aircraft" .......this would normally warrant an AAIB correspondence investigation.

They ought to be involved given that (from the press release) the operator's and manufacturer's investigations are inconclusive.

As SASless said

Originally Posted by

it wasn't just a bit of yawing but was two and half full rotations....

To my mind it warrants a deeper look, there's almost certainly some learning in there somewhere.

[Bell_ringer]

What is the definition of an incident?
If there was no damage, the issue didn't occur during a flight but during a test, does it fall within the jurisdiction of the accident board?

[Dai Whirlybird]

Originally Posted by Bell_ringer

What is the definition of an incident?
If there was no damage, the issue didn't occur during a flight but during a test, does it fall within the jurisdiction of the accident board?

The unexplained loss of control of an aircraft at Flight idle ticks my serious incident box, as I understand it injury or airframe damage is not a prerequisite of the AAIB's involvement. If I were flying that type I'd want a considered explanation, or at least an honest admission that it had not been possible to identify the cause.

As it stands and based upon the operators press release we have neither.

[booke23]

Originally Posted by Bell_ringer

What is the definition of an incident?
If there was no damage, the issue didn't occur during a flight but during a test, does it fall within the jurisdiction of the accident board?

On their website, the AAIB say they investigate accidents and serious incidents (where an accident nearly occurs, but no damage). It seems the threshold for investigating incidents seems to be much higher for small privately operated aircraft vs commercially operated aircraft.

2 and a half undemanded rotations.......it seems only pure luck and skill the aircraft didn't end up on it's side. This incident surely falls into the "serious incident to commercial aircraft" category.

Maybe the AAIB have picked this up now, but I read an article a month ago stating the AAIB had been informed but were taking no further action. I'm not sure this was the right decision.

[Bell_ringer]

900 degrees of undemanded rotation certainly sounds like it warrants a looksee but then with little detail available about the severity of the yaw and the intervention required to save the ship, the AAIB may have been satisfied by the manufacturers findings.
No doubt other 429 operators will be looking for a bit more information from Bell.

[cameron429]

The Emergency AD was issued after Bell submitted an ASB after our TGB was found to be loose. They were investigating another 1/2 units found to have issues and were apparently just about to issue an ASB when ours was found by pure chance.
The Wiltshire problem seems to be unrelated to the AD issued regarding loose TGB's.
We are awaiting a resolution at the moment but there is more work required than just replacing the Gear Box im afraid. We have been offline nearly a month so far, but are hoping to be back in the air within the next 10 days or so.

[Dai Whirlybird]

I hear that the WOG (wheels on ground switch) failed shortly after this airframe returned into service following the undemanded yaw incident - here's a question or two.....

Given that PAC (Power assurance check)s are done when light on the wheels, Is it feasible that the WOG micro-switch can cycle on and off in this configuration or is it isolated by software when conducting the PAC?

The WOG switch undoubtedly feeds it's status into the ADIU (Aircraft Data Interface unit) so is it possible that a cycling WOG switch or an intermittent fault with it could create confusion within the ADIU and generate spurious control inputs? What I don't know is whether the AFCS / AP configuration when conducting a PAC will permit or prevent this.

A further question....Are there any modifications or tweaks made to the WOG system when the 429's landing gear is converted from wheels to skids?

[212man]

I find it hard to believe that an airframe would have been converted from wheels to skids?

[Dai Whirlybird]

Originally Posted by 212man

I find it hard to believe that an airframe would have been converted from wheels to skids?

Ok, poor wording on my part - the B429 is available with either type of undercarriage. The thrust of my questioning is really trying to establish what differences exist, (if any) between the WOG system on wheeled and skidded versions, given that the WOG system is clearly designed for the former and I suspect might need some tweaking for use on the latter.

[Bell_ringer]

It may be a similar setup to the 407 which has a pressure switch on the rear skid mount. They can occasionally act up.
Just means the hobbs won't clock correctly.

[vaqueroaero]

Originally Posted by Bell_ringer

It may be a similar setup to the 407 which has a pressure switch on the rear skid mount. They can occasionally act up.
Just means the hobbs won't clock correctly.

Small point, it's on the front cross tube, not the rear.

[Bell_ringer]

Originally Posted by vaqueroaero

Small point, it's on the front cross tube, not the rear.

Whoops noted. It also activates the "center cyclic" warning if I recall, so when that fails to illuminate it's usually a sign it's broken.

[vaqueroaero]

Originally Posted by Bell_ringer

Whoops noted. It also activates the "center cyclic" warning if I recall, so when that fails to illuminate it's usually a sign it's broken.

Close! If the light illuminates and stays on then the switch is broken.(typically though it's out of alignment).

[Bell_ringer]

Originally Posted by vaqueroaero

Close!

Dammit!
We fly on the other side of the road here, probably why everything is the other way round