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A rapid demise of a TBM in icing conditions

The incident was already discussed here but I doubt many people came across it there.

I think it is worth discussing separately. There is no way for me to relocate postings to a new thread so I will move a little bit to this one.

The video is here

My take on it is that he lost control of the plane, took it way through Vne (or maybe over-stressed it), which on a TBM will take only 5-10 seconds, which broke off the wing, and after that he was obviously finished.

The loss of control may have been wing icing, or an elevator stall. Almost nobody knows how to recover from an elevator stall. There are some good videos on it but the reaction time may not be available even if you know how…

Otherwise, loss of wing lift due to heavy ice can be dealt with by pushing the nose down and letting airspeed build up, and that should also eventually get you out of the severe icing zone.

That one could get so much ice in a few minutes doesn’t suprise me at all. I’ve had it myself, in totally nonconvective conditions at 4000ft.

Were there CBs in the area? I can get radar archives for Europe (meteox.com can go back a fair bit) but don’t know of any US ones.

I wonder if the “rattle” at 9:30

was actually a stall buffet? That – even if misidentified – should be an instant clue to get the nose down.

Obviously the video of the aircraft going down is a fake because in that it is intact, with both wings attached.

Last Edited by Peter at 10 Nov 09:43
Administrator
Shoreham EGKA, United Kingdom

This is a tricky armchair exercise.

I wondered if the reference to “rattle” was ice breaking off, from the prop or from the wings slinging against the airframe, or if he was referring to them being rattled, bounced about.
It is certainly not evident that the pilot communicated any specific major concern about icing other than that reference.

I have recovered from a fugoid incident at FL270 which had the beginnings of an incipient spin, and I can relate under those conditions under heavy G loadings, a second is a long time, and it took several vital seconds for me to even understand what was happening, let alone what to do about it.

A sobering tale indeed.
E

eal
Lovin' it
VTCY VTCC VTBD

Of course the video is fake, because it was done with the Xwing simulator, Nevertheless the film is very impressive, especially the radio calls …
This accident was discussed extensively on COPA and other forums too.

I think it shows well that NONE of us is safe in icing conditions. When people like german editors of GA magazines brag how they flew in IMC/icing conditions over the Alps in a new FIKI Cirrus and mention how they nevertheless felt quite safe (“after all we would still have CAPS in case…”) then he should think again after watching this film. And an SR22 is a MICKEY MOUSE airplane compared to a TBM700.

I know why i stay out of any icing conditions (even with TKS).

It is hard to imagine (although probably technically possible!) how a TBM wings breaks of in a dive. I’ve watched them building the TBM in Tarbes and I still have the photos… the main spar looks like a part of the Golden Gate bridge …

Maybe it came apart when he tried to recover from the dive?

Whatever, this was not a beginner pilot and the whole thing happened in less than 5 minutes!

The rattle could well be vibrations of the tail caused by turbulent airflow from the wings after the ice buildup became too high …

Last Edited by Flyer59 at 10 Nov 11:06

Here’s a link to the NASA tailplane icing video:


Well worth watching if you haven’t already seen it.

There’s also a thread running on this accident on PPLIR. It shows data on the aircraft’s altitude and groundspeed as it entered the icing. It’s amazing how quickly the climb rate and groundspeed reduced over only about five minutes. It does suggest to me that the autopilot may have been on and flown the plane into the stall as it kept pitching the nose up trying to maintain the climb rate. It would also have the effect of exposing more of the airframe to ice accretion.

On the subject of autopilots: I don’t know if the A/P in a TBM has envelope protection or not. The DFC 90 I fly does but I don’t know if it is clever enough to recognise that the stall speed will increase as ice accretes: I suspect not.

[Youtube link fixed – please use the Share link – see Posting Tip – Peter]

Last Edited by Peter at 10 Nov 12:03
EGSC

The FAA page on N731CA is here.

Interesting debate here.

Apparently the rubber boots have a fixed periodicity, with a 53 second inactive timeslot, and cannot cope with a too-rapid ice accretion.

A track log of the climb (from the above 2011 thread) is here

Fairly obviously he started up icing heavily around 16k.

The aircraft was a 2005 TBM700, S/N 332, and would not have the G1000 and therefore would not have the GFC700 autopilot. The system would be the EFIS-40 and the KFC325.

However I don’t think any GA autopilot recognises this kind of problem. How could it? There is no easy to detect difference between e.g. airframe drag going up (due to ice) and you flying into a downdraught (which happens all the time in flying over any kind of terrain). The difference is a subtle change in pitch behaviour versus engine thrust. I believe the KFC325 does modify its control loop parameters according to the TAS (or IAS) – which the KFC225 doesn’t do – but that is about it as far as “intelligence” goes.

Last Edited by Peter at 10 Nov 12:19
Administrator
Shoreham EGKA, United Kingdom

It is not a coincedence that autopilot usage in icing conditions is restricted and even prohibited in many airplanes. Remember the Colgan Air accident in Buffalo?

Most autopilots will trim the airplane until the forces get too high – and then suddenly disconnect. A completely ice covered airplane that is out of trim cannot be recovered under most circumstances.

The C310 accident in Germany (1991) was under autopilot operation, just as Colgan Air, the TBM or the ATR72 at Roselawn (near Chicago).

All of these accidents are very similar in a way. All on autopilot, rapid icing, sudden autopilot disconnect and subsequent crash …

(The DFC90 autopilot IS NOT to be used in icing conditions, and I bet it’s the same for the DFC700). Both of these autopilot do not have Angle of Attack indication, and are based only Air Speed, so (i assume) the result would be pretty much the same. But that is my guess only, I do know that for sure.

Last Edited by Flyer59 at 10 Nov 12:35

However I don’t think any GA autopilot recognises this kind of problem.

No autopilot recognises this problem. This is why we still don’t have pilotless aircraft, even drones have a pilot sitting somewhere in a shelter who monitors the instruments. And this is why it is so important to monitor the instruments even when flying on autopilot in the cruise. Of course I don’t know if this pilot did monitor his and what he saw was simply beyond his and his aircrafts capabilities.

Apparently the rubber boots have a fixed periodicity, with a 53 second inactive timeslot, and cannot cope with a too-rapid ice accretion.

Every deice boot installation that I have come across has a manual mode to complement the automatic mode. The automatic cycles never really fit the actual ice accumulation: They are either too quick, only shifting a thin layer of ice around instead of shedding it or too slow as in this case. Therefore the best thing is to operate the boots manually whenever a given layer of ice (usually 5 to 10 millimetres) has formed.

Last Edited by what_next at 10 Nov 12:29
EDDS - Stuttgart

[Youtube link fixed – please use the Share link – see Posting Tip – Peter]

Sorry but the link doesn’t work for me.

EGSC

the link doesn’t work for me.

This is the basic Youtube page that people normally go to initially, with the Share function circled in red

When you click on it you get this (circled in red)

Copy/Paste that straight into your EuroGA post.

Alternatively the base URL from the Youtube page i.e.

http: / / www .youtube.com/watch?v=_ifKduc1hE8&

could be dropped in. Best to chop off the “feature=youtu.be” which sometimes appears in Youtube URLs – we will probably modify the text processor here to chop that off automatically. (I had to put a few spaces in the above URL to make it come up literally and not insert the video).

Last Edited by Peter at 10 Nov 14:34
Administrator
Shoreham EGKA, United Kingdom

Thanks!!

EGSC
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