Go Back  PPRuNe Forums > Aircrew Forums > Rotorheads
Reload this Page >

AS350 crash due to Jack Stall...

Rotorheads A haven for helicopter professionals to discuss the things that affect them

AS350 crash due to Jack Stall...

Old 24th Nov 2023, 06:22
  #1 (permalink)  
Thread Starter
 
Join Date: May 2003
Location: The Wild West... and Oz
Posts: 866
Received 9 Likes on 2 Posts
Wink AS350 crash due to Jack Stall...

Interesting video...
Apologies if posted before.


BigMike is offline  
Old 24th Nov 2023, 06:41
  #2 (permalink)  
 
Join Date: Sep 2002
Location: Great South East, tired and retired
Posts: 4,366
Received 203 Likes on 92 Posts
Speed, weight, and vigorous cyclic movement = soiled underwear at the minimum.
Ascend Charlie is online now  
Old 24th Nov 2023, 07:38
  #3 (permalink)  
 
Join Date: Jul 2017
Location: UK
Posts: 458
Likes: 0
Received 104 Likes on 72 Posts
The cyclic movement/pushover didn't look that vigorous to me? Is this something that the AS350 is particularly prone to?
hargreaves99 is offline  
Old 24th Nov 2023, 07:41
  #4 (permalink)  
 
Join Date: Jul 2014
Location: South East Asia
Age: 54
Posts: 320
Received 32 Likes on 21 Posts
Originally Posted by Ascend Charlie
Speed, weight, and vigorous cyclic movement = soiled underwear at the minimum.
you forgot "Altitude" into the mix, VNE goes down 3 knots for every 1000ft, if they are at 6000ft (judging from the tree line) VNE is close to 130Kts.
Agile is offline  
Old 24th Nov 2023, 07:54
  #5 (permalink)  
 
Join Date: Oct 2009
Location: Australia
Posts: 119
Received 33 Likes on 19 Posts
Iím not really familiar with the 350 but know itís susceptible to Jack stall. I donít know enough about that to comment.
When watching my initial thought was itís retreating blade stall, heís obviously high, heís gets a lot of speed in the dive then pitches up and rolls right at the moment he aggressively pulls the cyclic back.
Lucky to be alive looks like the deep snow save them
SLFMS is offline  
Old 24th Nov 2023, 08:26
  #6 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,573
Received 413 Likes on 218 Posts
All I can see is the deep snow.

Either that, or the page is blank.

edit: The link appeared when I clicked on ďquoteĒ.

A similar scenario to the Colin McCrae accident, by the looks of it.
ShyTorque is offline  
Old 24th Nov 2023, 08:33
  #7 (permalink)  
 
Join Date: Jul 2017
Location: UK
Posts: 458
Likes: 0
Received 104 Likes on 72 Posts
Looking again at the video he seems to push the cyclic abruptly forward at 1:05, (speed increases, passengers woop for joy) then cyclic back and right roll at 1:15

hargreaves99 is offline  
Old 24th Nov 2023, 09:00
  #8 (permalink)  
 
Join Date: Oct 1999
Location: Den Haag
Age: 57
Posts: 6,244
Received 330 Likes on 183 Posts
Originally Posted by SLFMS
Iím not really familiar with the 350 but know itís susceptible to Jack stall. I donít know enough about that to comment.
When watching my initial thought was itís retreating blade stall, heís obviously high, heís gets a lot of speed in the dive then pitches up and rolls right at the moment he aggressively pulls the cyclic back.
Lucky to be alive looks like the deep snow save them
I think the symptom are similar
212man is offline  
Old 24th Nov 2023, 09:22
  #9 (permalink)  
 
Join Date: Feb 2000
Location: UK
Posts: 1,680
Likes: 0
Received 129 Likes on 82 Posts
If I was going to put money on it, RBS would be my choice. The occupants (assuming that they all survived), are very lucky.! One of my early jobs on S&R was recovering the personal effects of my predecessor from the remains of an RBS induced crash on the South coast which killed three. - deep snow is useful !
Cornish Jack is offline  
Old 24th Nov 2023, 11:59
  #10 (permalink)  
 
Join Date: Jul 2004
Location: Europe
Posts: 433
Received 20 Likes on 12 Posts
If I have got all the informations right, that accident happened in 2016 and the accident report is already out. It was servo transparency aka. jack stall. The Company was TRK helicopters. Everybody walked away.
Rotorbee is offline  
Old 24th Nov 2023, 12:43
  #11 (permalink)  
 
Join Date: Mar 2010
Location: Hamburg
Posts: 162
Likes: 0
Received 6 Likes on 3 Posts
This appears to be the accident in question:

"Summary
On 16 March 2016, at 1618 Pacific Daylight Time, the TRK Helicopters Ltd. Airbus Helicopters AS 350 FX2 helicopter (registration C-FBLW, serial number 2955) departed from the base of a ski run approximately 82 nautical miles northwest of Smithers, British Columbia, on a day visual flight rules flight to the base camp (located approximately 7 nautical miles south-southeast of the ski run), with the pilot and 6 passengers on board. Approximately 1 minute after takeoff, while operating at low altitude, the pilot initiated a descent into a ravine. During the descent, the helicopter's airspeed increased rapidly. Moments later, the helicopter abruptly rolled to the right, pitched up, and collided with terrain on a steep snow-covered slope. There were no injuries, and all 7 occupants egressed the aircraft. The helicopter was substantially damaged. There was no post-impact fire and the emergency locator transmitter did not activate."

https://www.tsb.gc.ca/eng/rapports-r.../a16p0045.html
Stuart Sutcliffe is offline  
Old 24th Nov 2023, 12:58
  #12 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 10,317
Received 622 Likes on 270 Posts
What doesn't gel with the RBS/jackstall theory (they are so similar it's difficult to tell them apart) is the low Nr horn - that sort of disc loading produces high Nr not low.
crab@SAAvn.co.uk is offline  
Old 24th Nov 2023, 12:59
  #13 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 10,317
Received 622 Likes on 270 Posts
Shy - great tip about hitting quote to see the link - I have been having this problem with my browser for ages.
crab@SAAvn.co.uk is offline  
Old 24th Nov 2023, 14:37
  #14 (permalink)  
Below the Glidepath - not correcting
 
Join Date: Jun 2005
Location: U.S.A.
Posts: 1,874
Received 60 Likes on 18 Posts
...while operating at low altitude, the pilot initiated a descent into a ravine.
So, primary cause, servo transparency, secondary cause, lack of imagination.
Two's in is offline  
Old 24th Nov 2023, 16:13
  #15 (permalink)  
 
Join Date: Nov 2006
Location: After all, whatís more important than proving to someone on the internet that theyíre wrong? - Manson
Posts: 1,841
Received 51 Likes on 36 Posts
Originally Posted by [email protected]
What doesn't gel with the RBS/jackstall theory (they are so similar it's difficult to tell them apart) is the low Nr horn - that sort of disc loading produces high Nr not low.
The same horn also provides aural warning of low or high main rotor speed, that is, when the rotor is between 250 and 360 rpm (continuous sound) and above 410 rpm (intermittent sound).
​​​​​​​Have another listen - sounds like it worked as advertised.
RVDT is offline  
Old 24th Nov 2023, 16:25
  #16 (permalink)  
 
Join Date: Sep 2004
Location: Canada
Posts: 1,738
Received 149 Likes on 74 Posts
RTFM!
albatross is offline  
Old 24th Nov 2023, 17:23
  #17 (permalink)  
 
Join Date: Nov 2006
Location: After all, whatís more important than proving to someone on the internet that theyíre wrong? - Manson
Posts: 1,841
Received 51 Likes on 36 Posts
The reason for it - elastomeric bearings - i.e. the spherical bearing.


This bearing is multiple steel spherical cups separated by thin layers of rubber material. Not unique to the AS350.
It can bend and twist but not move so much in compression. Distorting the bearing takes some effort. The maximum effort is naturally at maximum pitch i.e. the retreating side and is always there.
In forward flight some of the disk is constantly stalled and even going backwards with regard to flow. Stall creates a shift in centre of lift aft on the blade and creates an additional feedback which is cumulative with speed and loading further outboard on the disk where it matters.
The forces are quite high and affect fatigue life and ultimate strength, I think the weak point is the PCL's which will possibly bend. Hence the HYD system was designed to be not strong enough to let this happen.
As it is at the edge or slightly outside of the certified flight envelope and marginally before RBS it seems to be acceptable.
Dual HYD aircraft in the same family which will not yield to feedback have a load cell (flat spring and microswitch) on one servo which will warn with a LIMIT caption to avoid overloading the control system.

There are warnings and limitations in the RFM. "Forewarned is forearmed" but maybe not communicated readily.

"Grey" 355 style wide chord blades may be more susceptible than the old "Blue" B model blades but even a B model is susceptible.
RVDT is offline  
The following users liked this post:
Old 24th Nov 2023, 19:08
  #18 (permalink)  
 
Join Date: May 2002
Location: Downeast
Age: 75
Posts: 18,283
Received 498 Likes on 207 Posts
This discussion has been had before....probably a couple of times.

Refresh my fading memory as to why just making stronger PCL's and marginally stronger hydraulic jacks would prevent the problem although allowing honest to goodness RBS?

I recall one wonderful old Sikorsky and a venerable Bell product that with youthful indiscretion could both demonstrate RGS for the young and dumb. (Hand raised!).

In those aircraft with correctly turning rotor heads, the nose would pitch up and roll left....and the airspeed would bleed off till the RBS abated or ceased....and assuming one was wise enough to reduce Collective to a reasonable cruise setting....normal flight returned.

Surely some Whirlwind experienced Pilots had some exposure to that.


In the early CH-47....A Models being grossly over weight could provide occurrences of reactions very similar to RBS but in both heads....and with contra rotating rotors....;think about how those symptoms were manifested!

SASless is offline  
The following users liked this post:
Old 24th Nov 2023, 20:58
  #19 (permalink)  
 
Join Date: Apr 2000
Location: EGDC
Posts: 10,317
Received 622 Likes on 270 Posts
Originally Posted by RVDT
Have another listen - sounds like it worked as advertised.
Good point RVDT, I didn't realise it had a high Nr warner as well.
crab@SAAvn.co.uk is offline  
Old 24th Nov 2023, 23:30
  #20 (permalink)  
 
Join Date: Oct 2007
Location: Here
Posts: 961
Received 3 Likes on 2 Posts
Originally Posted by [email protected]
Shy - great tip about hitting quote to see the link - I have been having this problem with my browser for ages.
This is a well known pprune problem and fix (reply). I seemed to fix mine by resetting the pprune cookies.

It went something like:-

Turning down/off ad blocker
Making sure cookies were enabled
Closing pprune
Clearing pprune cookies (will delete saved password)
loading pprune
logging on (needs password)
accepting cookies
Turning up/on ad blocker

jimjim1 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.