View Full Version : N690LS Turbo 690B Commander
ONE GREEN AND HOPING
22nd Oct 2021, 09:16
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. ?
DaveReidUK
22nd Oct 2021, 11:16
Preliminary Report (https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/103984/pdf)
ONE GREEN AND HOPING
25th Oct 2021, 10:55
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.
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.
DaveReidUK
25th Oct 2021, 12:54
"The wreckage was distributed in a diameter of about 50 yards" doesn't sound like an in-flight breakup to me.
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.
"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.
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.
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.
DaveReidUK
1st Nov 2021, 22:50
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.
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.
https://m.youtube.com/watch?v=vTQwkKameLg
DaveReidUK
4th Nov 2021, 12:42
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 ?
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.