Bell 429 - undemanded yaw question
 

Are there any 429 operators out there who have had instances of undemanded yaw, either on the ground or in the air?
One happened recently in UK and it would be educational to know if has happened elsewhere - thanks.

It would appear there is some history although it’s not clear what nature the symptoms of this last incident were:

https://www.flightglobal.com/news/ar...rators-420608/
Bell 429 TR Pitch Change Link Bearing Failure - Aerossurance

Thanks - but as I understand it the aircraft yawed left in the middle of a PAC.

was the sab systems switched off or on?

Also...what was the Yaw Pedal position immediately prior to this sudden yawing?

What kind of surface was the aircraft on at the time?

I can think of several relevant questions particularly if there are no mechanical defects found that would explain the event.

Sas - to my knowledge there were no extenuating circumstances - a post maintenance ground run with a very experienced pilot both on type and in role. Apparently, the downloaded data showed a yaw input of less than 1 sec so TR servo would be suspect - I assume the AP would be engaged for a PAC.

Crab: Speaking to my colleagues in America yes, the AP should be disengaged for PAC.

Crab:
we had a servo problem,not with the tailrotor, but the cyclic. It was discover during the daily check.

KK:
Nothing prevent the crew to do a power check without the AP, I guess it depend of the company SOP.
FH

Yup - been there done that. Auto pilots coupled up and all of a sudden it yaws about 45 degrees left and then straightened itself up. We left it coupled and then it happened again, so we uncoupled and flew home. If I remember correctly the factory set pedal friction was too tight and the autopilot over compensated for it.

vaqueroaero:
did your event occur in flight or in hover?
Cheers
FH

In flight. I believe all we had was the three axis autopilot at that point in time.

WAA grouded
 

I suspect that out of the 39 or so HEMS machines around the bazaars, it is likely that more than one of them will be waiting for some spares at any one time - when you say 'still on the ground' is this an ongoing issue?

Cheers

TeeS

Not sure if it's related, but an emergency A/D has just been released by Transport Canada regarding loose tail rotor gearbox's on 429's

http://publicapps.caa.co.uk/docs/33/CF201818E.pdf

TeeS, your right when you say that at any one time there are a number of aircraft waiting for spares. I thought as a air ambulance they would declare the aircraft AOG in order to have priority over others, unless this did not happen in order to save money!

Wiltshire Air Ambulance Bell still offline
 

Wiltshire air ambulance is still offline, is this true?

Yes. Wiltshire's 429 has been offline for a month now, apparently a Bell Test Pilot has visited.

To Bell's credit they are clearly taking this incident very seriously,

Surely there will be a press release from the WAA, it's been very quiet on that front!

Still waiting for this press release!!

Seems a Two Bit Explanation to me!:*

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

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.

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.

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

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.

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.

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?

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.

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.

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

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