N690LS Turbo 690B Commander
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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. ?
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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.
Very, very mysterious.
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.
Very, very mysterious.
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.
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.
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.
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 ?
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 ?
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 15:54.
