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| | |-+  TBM-700 N731CA crash outside of MMU
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Author Topic: TBM-700 N731CA crash outside of MMU  (Read 33798 times)
gsaviator
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« Reply #30 on: December 24, 2011, 11:31:44 AM »

My guess is that on this particular airfoil and configuration, the laminar boundary layer gets disturbed very easily, resulting in separated flow, and loss of lift and control.  So the system has to be used immediately, just as the AD says.  It says clearly that there have been incidents and an accident due to this.



The problem is really a two edge sword. You are correct saying the boudary layer gets disturbed very easily. Most new complex airfoils are very sensitive to any variation or disturbance to airflow hense why the FAA says they want you to use the boots at the first sign of ice. I have flown certain corporate jets that have (I'll keep this simple) one or two small triangle pieces the size and thickness of a dime attached to the leading edge of the wing which make a huge aerodynamic change to the airflow on the wing. Granted a corporate jet is designed to fly higher and faster than a TBM wing but it does tell one how a small item can make a difference; So, any ice accumulation can be huge.  

The next problem is how a boot actually works. I have been flying for over 21 years professionaly and a boot will not shed ice until it gets a significant amount of ice built on the surface. To little ice, and the ice will just expand with the boot and not shed. Then you can be basically screwed to the point where you cannot shed the ice properly once more ice builds.

The problem is certainly a catch 22.
« Last Edit: December 24, 2011, 11:38:05 AM by gsaviator » Logged
phaques
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« Reply #31 on: December 24, 2011, 05:53:02 PM »

Medflight5 -

Can you share the precise feeds - and time slots - you used to piece together your montage? I can't find them in the archives.

Thx.
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Jason
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« Reply #32 on: December 27, 2011, 02:58:48 PM »

Here's an interesting weather analysis from Scott Dennstaedt, a former NWS meteorologist, regarding the TBM700 crash.

http://avwxworkshops.com/forum/read.php?8,443
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rduke007
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« Reply #33 on: December 28, 2011, 01:15:12 PM »

I see a profound lack of two issues being discussed in this conversation.
1. The effects of high AOA on icing characteristics.
2. The type of autopilot available to the TBM 700, and most-likely mode it was in (if on) at the time of the upset.
Most aircraft that don't have autothrottles would have either pitch hold, or rate hold. I have found the latter easier to use predictably in the light aircraft i fly, and use autopilots a lot, particularly during single pilot IFR.
Many booted types have had difficulty shedding ice in anything other than clean configuration straight & level flight. A lot of operators stopped flying this type of equipment (booted aircraft) in northern latitudes for transport category after the ATR Roselawn accident.What if the ice accreted where it wasn't easily seen?
Departures in this airspace often provide a host of distractions that could keep one focused on nav related tasks while the autopilot continued to sacrifice airspeed to try & regain it's programmed FPM climb rate. It may not be possible to determine whether the autopilot was even engaged, although microscopic analysis can usually tell if a lamp was illuminated during an accident sequence (filament stretching, as opposed to the cold fracture one would find if unlit)
It is also easy for us instructor types to say 'yes' to someone who has at least met the minimum requirements (i.e. instrument rating) and has equipment which appears, at least on paper, to handle a good share of the weather thrown its way.
It is disconcerting to those who fly to think it could happen to us, so we rationalize and eventually find "pilot error."
There is hazard in stopping there, and failing to understand how the combination of a recently certificated instrument pilot, an aircraft that appears on the surface to be all weather capable, and instructors who don't necessarily have to follow any specific syllabus for the transition from the trainer to the TBM. We don't teach judgment, but what we do as instructors has the largest impact on whether the pilots we turn out will go on to develop good judgment.
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medflight5
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« Reply #34 on: December 28, 2011, 04:28:07 PM »

Medflight5 -

Can you share the precise feeds - and time slots - you used to piece together your montage? I can't find them in the archives.

Thx.

KEWR New York Departure and NY Appch (Liberty West/South)
Audio was compiled from the 0930L (1430Z) and 1000L (1500Z) feeds from both.

His initial contact with ATC is at 09:51:49L (14:51:49Z)
« Last Edit: December 28, 2011, 06:09:24 PM by medflight5 » Logged
phaques
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« Reply #35 on: December 28, 2011, 06:57:59 PM »

Thanks - I found them all. First contact is with NY Departure at about 0949 as he is checks in after the handoff from tower at 800 feet.

A question: What is the normal climb performance of a TBM700 and how much does it normally deteriorate as the plane climbs into the low to mid teens? The Flightaware track log shows his airspeed and rate of climb dropping off precipitously as he climbs past 13,000ft, but I wonder how much the change might be due to normal performance changes? In the King Air E90, climb airspeed drops from 150kts to 130kts as you pass through 10,000 feet - does anyone know if there is a similar rate of change for the TBM?. I'd like to get an idea how much of his declining performance is attributable to ice.

Thanks.
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sykocus
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« Reply #36 on: December 29, 2011, 06:53:34 AM »

Thanks - I found them all. First contact is with NY Departure at about 0949 as he is checks in after the handoff from tower at 800 feet.

A question: What is the normal climb performance of a TBM700 and how much does it normally deteriorate as the plane climbs into the low to mid teens? The Flightaware track log shows his airspeed and rate of climb dropping off precipitously as he climbs past 13,000ft, but I wonder how much the change might be due to normal performance changes? In the King Air E90, climb airspeed drops from 150kts to 130kts as you pass through 10,000 feet - does anyone know if there is a similar rate of change for the TBM?. I'd like to get an idea how much of his declining performance is attributable to ice.

Thanks.
Don't put too much weight on the speed from flightaware. That's the ground speed from radar not the plane's airspeed.
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rduke007
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« Reply #37 on: December 29, 2011, 03:28:17 PM »

Groundspeed would be directly related to airspeed and winds, and winds on that day should have produced an increase, so the log is a "tell" in my opinion.
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MikeNYC
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« Reply #38 on: December 29, 2011, 05:12:13 PM »

rduke, but the aircraft as it climbs will encounter different winds aloft at various altitudes which will all affect the groundspeed differently.
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rduke007
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« Reply #39 on: December 31, 2011, 05:32:44 PM »

This was discussed on Bill Waldock's Facebook page, and winds aloft for the time in question should have produced an increase in groundspeed as the aircraft turned southwest during the climb. Waldock is a recognized expert, and often sought after as an expert witness during litigation. This doesn't make his facebook friends automatically correct, but what I recall reading seemed to be based on accurate data. A lot of those folk are people who studied with Bill as their professor at Embry-Riddle, in the crash lab at the Prescott, AZ campus (where I graduated in 1990.)
Airspeed can be extrapolated from pressure & temperature records,as well as wind vectors, and my opinion, having seen the chart, is that the accident aircraft lost airspeed and climb rate. This is consistent with an airframe icing scenario. It is quite possible that at higher angle of attack, the ice accreted somewhere it wasn't detected, or could be addressed by the available deicing gear, and that the AP in FPM climb mode could well have held the plane in a smooth climb while slowly reducing airspeed until an aggravated stall occurred. If this was sudden, and unexpected, the loading conditions and the surprise factor could have easily resulted in loss of control, or even a spin. This, of course, is educated speculation on my part, and one possible causation scenario. But regardless of the eventual determination by the board, does this discussion change anything for the readers checklist in how we fly & manage traffic under these conditions?
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frcabot
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« Reply #40 on: April 10, 2014, 03:44:09 PM »

http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20111220X20005&key=1

Probably similar to what happened to N702H.

I think the probable cause report is a little unfair. Criticizes him for entering "severe" icing but no severe icing was forecasted and even the pilot himself only reported light icing. That three other flight crews reported severe icing doesn't mean the icing was actually "severe" icing as defined by the FAA, let alone for him at a different time and in a different location, and in a different airplane. The Socata is certified for FIKI, even if it's not for severe icing (AFAIK, the definition of severe icing is that the ice accretes faster than the de-icing system can remove it, so I'm not sure what plane could be certified for "severe" icing). According to the full narrative, the pireps about severe icing were made at 0749, 0808, and 1042. His crash occurred at at about 10:05, well after the 0749 and 0808 pireps had been made (and in different areas), and before the 1042 pirep. Plus, there's no evidence that the ATC controller ever advised him of these pireps other than to remind him about "moderate" icing between 15 and 17K.

Also, says the pilot failed to depart the icing area but that's exactly what the pilot was doing. I sure hope the NTSB never writes a probable cause determination like that in my case.

The perplexing thing about the N731CA accident is that the pilot voluntarily departed VMC to enter known IMC and icing conditions. That's pretty poor judgment. Even if you think your plane is capable of handling moderate icing conditions, why would you ever want to tempt fate?
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InterpreDemon
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« Reply #41 on: April 10, 2014, 04:48:07 PM »

"I sure hope the NTSB never writes a probable cause determination like that in my case."

I sure hope the NTSB never has a need to write any probable cause determination in my case... or yours smiley
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frcabot
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« Reply #42 on: April 11, 2014, 11:32:02 PM »

"I sure hope the NTSB never writes a probable cause determination like that in my case."

I sure hope the NTSB never has a need to write any probable cause determination in my case... or yours smiley
Touche.
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