Go Back  PPRuNe Forums > Non-Airline Forums > Accidents and Close Calls
Reload this Page >

N690LS Turbo 690B Commander

Accidents and Close Calls Discussion on accidents, close calls, and other unplanned aviation events, so we can learn from them, and be better pilots ourselves.

N690LS Turbo 690B Commander

Old 22nd Oct 2021, 10:16
  #1 (permalink)  
Thread Starter
 
Join Date: Jul 2006
Location: At home, occasionally
Posts: 131
N690LS Turbo 690B Commander

28SEP21 Accident during aero survey sortie in which the 1975 registered aircraft may have suffered a catastrophic structural failure during the cruise at 15000ft. Appeared to have rapidly reduced ground speed from @200kts to @90 kts, then entered spin to surface level in @1 minute. Any body know more detail or preliminary findings beyond the obvious tragedy regarding the 3 SOBs lost. ?
ONE GREEN AND HOPING is offline  
Old 22nd Oct 2021, 12:16
  #2 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 13,360
Preliminary Report
DaveReidUK is online now  
Old 25th Oct 2021, 11:55
  #3 (permalink)  
Thread Starter
 
Join Date: Jul 2006
Location: At home, occasionally
Posts: 131
Yup, Thanks I read that item as well.... Doesn't really throw any light on what could have been the obtaining of any specific evidence concerning suspected structural failure.
ONE GREEN AND HOPING is offline  
Old 25th Oct 2021, 12:46
  #4 (permalink)  
 
Join Date: Dec 2001
Location: FL, USA
Posts: 2,795
That could be a propeller problem or an engine failure with a resultant loss of control.
Not necessarily an Inflight breakup due to structural failure.
B2N2 is offline  
Old 25th Oct 2021, 13:54
  #5 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 13,360
"The wreckage was distributed in a diameter of about 50 yards" doesn't sound like an in-flight breakup to me.
DaveReidUK is online now  
Old 1st Nov 2021, 14:26
  #6 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 910
Originally Posted by B2N2 View Post
That could be a propeller problem or an engine failure with a resultant loss of control.
Not necessarily an Inflight breakup due to structural failure.
Hmmmm, an engine problem (unless complete double engine failure with altitude hold engaged an no intervention until the stall - but how likely would this be???) should not lead to a loss of 110kts within one Minute of straight and level flight!? And all this in day VMC. That said, a propeller going into Beta/Ground idle at 200 kts could potentially cause quite some drastic effects.
Very, very mysterious.
henra is offline  
Old 1st Nov 2021, 14:30
  #7 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 910
Originally Posted by DaveReidUK View Post
"The wreckage was distributed in a diameter of about 50 yards" doesn't sound like an in-flight breakup to me.
Leaving aside that I'm not aware of such a case with an AeroComander we have seen e.g. wingtips fold up in flight but not totallly separate on light aircraft before. Not saying this was the case here. But from the diameter of the wreckage we cannot safely exclude that some kind of major inflight structural problem has occured.
henra is offline  
Old 1st Nov 2021, 19:42
  #8 (permalink)  
 
Join Date: Dec 2001
Location: FL, USA
Posts: 2,795
Originally Posted by henra View Post
Hmmmm, an engine problem (unless complete double engine failure with altitude hold engaged an no intervention until the stall - but how likely would this be???) should not lead to a loss of 110kts within one Minute of straight and level flight!? And all this in day VMC. That said, a propeller going into Beta/Ground idle at 200 kts could potentially cause quite some drastic effects.
Very, very mysterious.
A single engine failure with a late autopilot disconnect can have catastrophic effects.
B2N2 is offline  
Old 1st Nov 2021, 21:12
  #9 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 910
Originally Posted by B2N2 View Post
A single engine failure with a late autopilot disconnect can have catastrophic effects.
Indeed it can. But I doubt you would lose 110kts (going from 200kts to 90kts) in just 60s in straight and level flight.
henra is offline  
Old 1st Nov 2021, 23:50
  #10 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 13,360
henra

Hmmmm, an engine problem (unless complete double engine failure with altitude hold engaged an no intervention until the stall - but how likely would this be???) should not lead to a loss of 110kts within one Minute of straight and level flight!? And all this in day VMC. That said, a propeller going into Beta/Ground idle at 200 kts could potentially cause quite some drastic effects.

The latter is one of the few reasons I can think of that would produce such a rapid deceleration in level flight.
DaveReidUK is online now  
Old 3rd Nov 2021, 23:21
  #11 (permalink)  
 
Join Date: Dec 2001
Location: FL, USA
Posts: 2,795
I disagree, prop going into flat pitch or even worse Beta would cause such an aggressive yaw and roll that the airplane would be upside down in mere seconds if that.
I doubt the autopilot was three axis, so no rudder input.
Engine failure would lead to increasing aileron deflection to maintain heading till full defection and autopilot disconnects and and asymmetric stall leads to a spin.

Beech Queenair accident but imagine flying 200kts and a prop going beta.
You’d be upside down before you knew what happened.

B2N2 is offline  
Old 4th Nov 2021, 13:42
  #12 (permalink)  
 
Join Date: Jan 2008
Location: Reading, UK
Posts: 13,360
Originally Posted by B2N2
I disagree, prop going into flat pitch or even worse Beta would cause such an aggressive yaw and roll that the airplane would be upside down in mere seconds if that.
I doubt the autopilot was three axis, so no rudder input.
Engine failure would lead to increasing aileron deflection to maintain heading till full defection and autopilot disconnects and and asymmetric stall leads to a spin.


Fair point, but the massive speed reduction in level flight is a fact, unless you are disputing the NTSB's initial findings.

What do you think caused that ?
DaveReidUK is online now  
Old 5th Nov 2021, 16:40
  #13 (permalink)  
 
Join Date: May 2010
Location: PLanet Earth
Posts: 910
Originally Posted by B2N2 View Post
Engine failure would lead to increasing aileron deflection to maintain heading till full defection and autopilot disconnects and and asymmetric stall leads to a spin.
Yes. But would the speed drop from 200 to 90kts within 60s???
Hint: Single engine best climb speed is 115kts, so they would have passed through that. Single engine rate of climb with prop feathered and gear retracted is 900fpm which is rather good for a light twin. So even with a not-feathered prop I have difficulties seeing it losing 110kts in under 60s.

Last edited by henra; 5th Nov 2021 at 16:54.
henra is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.