Behchoko Crash NWT??

[Maynard]

In reference to the credibility of the GFA's, i find this interesting. Tafs for YRL,YHD,YXL all have -fzdz, the 06Z clouds and weather looks like: yet the icing looks like this:
. Am I missing something here?

[Diadem]

I'd say it's probably something to do with the fact that the GFAs you posted are for 1200Z, whereas the FZDZ at YRL is from 0100-0300, at YHD it's 0400-0800, and at YXL it's 0400-0800. That's like looking at the public forecast for tomorrow and then looking at the TAF for today and wondering why they show two different things.

[CpnCrunch]

I'd say it's probably something to do with the fact that the GFAs you posted are for 1200Z, whereas the FZDZ at YRL is from 0100-0300, at YHD it's 0400-0800, and at YXL it's 0400-0800. That's like looking at the public forecast for tomorrow and then looking at the TAF for today and wondering why they show two different things.

If you look at the GFA above it also shows freezing drizzle, but there is nothing at all on the icing chart.

Anyway, I find that it useful to believe the worst forecast I can find.

[Diadem]

If you look at the GFA above it also shows freezing drizzle, but there is nothing at all on the icing chart.

Anyway, I find that it useful to believe the worst forecast I can find.

The icing chart only shows icing if it's moderate or severe. I don't know whether light freezing precipitation meets that requirement, but I would suspect that because it's light and local it doesn't meet the criteria to be on the icing, turbulence and freezing level charts.

[StratusSmoke]

There is often an area a couple of hundred feet below stratiform clouds where there is some freezing precip even though there is none reaching the surface. I would imagine it becomes a real big problem when the space between the clouds and the ground gets pretty small. Difficult to forecast but I try to mention it in low stratus conditions and air temps -5 to -15. I strongly suspect that is what caught Nancy in Winnipeg.

Up til departure the YWG metar had 0C (5am), ... a north takeoff into 15-20kt blustery / light-snow ... turnout SE .. not very high and went down in 4 minutes. A W&B issue included (report / Oct 6 05 5:37). Meterological info in the report has 2C per 1000' ....

YZF/NWT here is -10C to -11C, but what's it at 3-4000' a few minutes later ? Less ?

What "caught" Nancy in YWG, was a warm airplane brought out into precip. Also know as a cantaminated wing on departure, plus the failure to maintain corrodinated flight (evidenced at the point of impact, loss of control while in flight) an attempt to maintain altitude, while the only defence at that point would be dashboard power and a controlled descent. That would have given her some say in where she ended up. Perhaps not graceful, but not a lawn dart. Hurt your feelings? Too bad, learn from it.
Illya

The accident report does not reflect any pre-take off icing or accumulation and seems to discount it as a factor (tactile check 12 minutes prior to flight).

Special wx obs taken 0531 shows temp -1C. The hourly was 0C, but no indication if that was on the minus side of 0 i.e. -0.4C.

Two minutes before ATD -2C at 1800 asl and -3C at 2400 asl.

[pdw]

Going for accurracy here ... -3C at 2400asl / -3C at 1600agl (YWG elev 783'asl) subtract [a compromise of -1/2C /31F at zero agl (0 to -1C/ 32F to 30F)] to -1C/30F to -2 to -2.5C (27F-28F) at 1600'agl which calculates a 1.2C(2.5F) to 1.5C(3F)/1000' lapse rate there. (Noticing a very-low to non-existant temperature gradient horizontally in this area as I'm checking weather history). That was the huge expanse of hang-back cloud trailing the early winter low system that had cleared well East of the area (from the day before).

Back to "Behchoko" (the TAF), it has the LO system/ front still approaching, with new cloud/icing generated from abundantly warm / high moisture. And so here it's an increasing temperature gradient flying to YFS on the westerly heading Nov 20, ... starting from -11C at the surface to where the "severe" icing is encountered.

[Redneck_pilot86]

There is often an area a couple of hundred feet below stratiform clouds where there is some freezing precip even though there is none reaching the surface. I would imagine it becomes a real big problem when the space between the clouds and the ground gets pretty small. Difficult to forecast but I try to mention it in low stratus conditions and air temps -5 to -15. I strongly suspect that is what caught Nancy in Winnipeg.

Up til departure the YWG metar had 0C (5am), ... a north takeoff into 15-20kt blustery / light-snow ... turnout SE .. not very high and went down in 4 minutes. A W&B issue included (report / Oct 6 05 5:37). Meterological info in the report has 2C per 1000' ....

YZF/NWT here is -10C to -11C, but what's it at 3-4000' a few minutes later ? Less ?

What "caught" Nancy in YWG, was a warm airplane brought out into precip. Also know as a cantaminated wing on departure, plus the failure to maintain corrodinated flight (evidenced at the point of impact, loss of control while in flight) an attempt to maintain altitude, while the only defence at that point would be dashboard power and a controlled descent. That would have given her some say in where she ended up. Perhaps not graceful, but not a lawn dart. Hurt your feelings? Too bad, learn from it.
Illya

The accident report does not reflect any pre-take off icing or accumulation and seems to discount it as a factor (tactile check 12 minutes prior to flight).

Special wx obs taken 0531 shows temp -1C. The hourly was 0C, but no indication if that was on the minus side of 0 i.e. -0.4C.

Two minutes before ATD -2C at 1800 asl and -3C at 2400 asl.

When I did my caravan sim at PAIFA in 2010, my instructor (Gene LaLonde) said he was contracted by the TSB to assist in the investigation. During the weeklong course we discuss virtually every caravan accident to date, around 200. He said this accident was the only one where the pilot did everything right and still got burned. She took off into unforecast severe icing, immediately requested a return when encountering same, and still crashed. I don't think Gene would make that claim lightly, and I don't think he would have missed it had she departed with airframe ice.

[Illya Kuryakin]

I don't thnk too much airframe ice would have been present at the crash sight? At best, these accidents are open to speculation. We had a company aircraft on approach to RWY 36 at the time of the accident, that reported no inflight icing.
Of course the best example of surface contamination was the Pelee Island accident. If I recall,
Nakina suffered a similar fate a few years back.
Illya

[pdw]

When into the maximum weights and forced into a 180 because of icing, there is real loadfactor concern (as mentioned once in a pod cast with reference to a Nebraska Caravan/icing accident a few years back). In YWG off 36 the 180-action is initiated in just 1.5 minutes (3 miles) after turning on the enroute heading of approx 110T ... with the immediate target to get back lined up for rwy 31. To return, the pilot is given '250M and to maintain the 1700agl'; but when 'unable', is offered 280M (ASN narrative/ Oct 6 05) which is into a strong crosswind again about 'mid turn', this time from the right.
Given that, and the approximate co-ordinates determined from other times, distances, and positions (info in the report), what 'rate of turn' accomodates these 220-230 degrees of track change required and what space is available for the turn radius needed to get from the left-crab heading of 105T onto the right crab heading of rwy 31's centerline ?

In "Behchoko" the 180-turn is being made with altitude to lose and also space for that type of low-rate turning; least precarious when void of any W&B issue.

[Donald]

At best, these accidents are open to speculation.
Illya

Bingo.

[pdw]

At best, these accidents are open to speculation. We had a company aircraft on approach to RWY 36 at the time of the accident, that reported no inflight icing.

Taxiing/backtracking for take-off (the 12 minutes between the "tactile" and the rotation) is a vulnerable time if some wet snow and the temperature is close to call. Once airborne, anything that got 'stuck on' in the pre-takeoff after the tactile would be going against you esp with the maxed load (see loading details described in the TSB report).

Of course the best example of surface contamination was the Pelee Island accident.

Must have already picked up some on the way if this quick turnaround flight was only minutes on the ground; ... of course any enroute collection resorts to surface upon touchdown.

If I recall, Nakina suffered a similar fate a few years back.

(EDIT ... no ground icing in the report ... a "rudder trim" idication error is listed as the cause)

This NWT accident appears to have very satisfactory loading, with the pre-takeoff tactile observation 100% in order upon departure. The downfall of this flight appears to be lots of unexpected liquid moisture ... more latent heat ... more supercooling etc, which perhaps wasn't suspected as being as significant as it was (or catching on as heavy as it was) along the particular flight-path this Caravan was taking.

[Illya Kuryakin]

Pelee Island sat in freezing rain before departure.

pdw, what was the W&B issue with the Morningstar machine? I still suspect from the timing, that things started to unravel on flap retraction? I usually suck up one notch of flap at about 400 feet.
Illya

[pdw]

Pelee Island sat in freezing rain before departure.

This is what's IMO believed to be correct. At the time a pilot at Put-in-Bay not far from CYPT noted that he decided to "pack it in by 5pm" because of freezing rain had started. A number of residents on the Island were quoted (I believe this group also included the Mayor if I recall correctly from media hype at the time) to have come out to their vehicles after work as news of the accident had spread to find evidence of freezing rain. Lets be clear though, that everyone who had boarded had done so well before this time, keeping in mind that pax-loading to go was being accomplished by 4:20pm (a 4:30pm departure), which was much earlier than the timing of those commentaries.

Yes there was freezing precip starting, yet it's possible that a warm windshield and hood, and with it being the high-wing it is, may not necessarily have made it look as alarming as it should have looked to this PIC once having climbed in to taxi for take-off. How would a no-go decision have unfolded here ? The ramp and runway were well salted, ... so then there really wasn't much of a cue left at that point either ... to reconsider.

pdw, what was the W&B issue with the Morningstar machine?

I drove through the area as that system was approaching, as a matter fact was heading for Edmonton to take in the Cessna Caravan Icing Seminar at Niska, scheduled the evening before this accident happened; was shocked to see it on the news the very next day after that lesson. Then at the time there was the info about about an incident to do with picking up ice, just a few days before this accident ... but at the front of this same system, to do with an inbound Van from Thunder Bay (the same one ?). The report for this accident discusses some uncertainty about the W&B information, but here everyone must read it verbatum from the report, not to misconstrue anything factual that the TSB has stated about that.

I still suspect from the timing, that things started to unravel on flap retraction? I usually suck up one notch of flap at about 400 feet.

If it is after turning enroute there at 500'agl, it's close to where the decision to land originates, about a minute to a minute-and-a-half after the 95 degree heading change into crosswind / into the strong but irregular (even slightly left-tailquartering) component for tracking the ThunderBay route ESE.

Speaking of flap, looking at the Behchoko accident photo, it's hard to see if they are up or down. An NTSB narrative of a Caravan landing event at Grand Island NE on the morning of Jan 20 1998 is somewhat similar, being at cruise power all the way down to make the field (the report contains the pilot's written statement) going 120-140kts, a speed obviously out of the park for extending flap.

[Redneck_pilot86]

Speaking of flap, looking at the Behchoko accident photo, it's hard to see if they are up or down. An NTSB narrative of a Caravan landing event at Grand Island NE on the morning of Jan 20 1998 is somewhat similar, being at cruise power all the way down to make the field (the report contains the pilot's written statement) going 120-140kts, a speed obviously out of the park for extending flap.

10 degrees of flap can be extended at 175 KIAS. 20 degrees at 150 and full flap at 125.

[pdw]

Copy that. At least an inch of ice there, in that context (Nebraska 1998 ... EDIT: I meant Grand Island NE ... on the Jan 20/ a 6am Van-departure as well; almost identical to "Bechoko" here ?).

[Illya Kuryakin]

Copy that. At least an inch of ice there, in that context (Nebraska 1998).

Are you comparing the ATR42/72 incident flap,extension with that of a Caravan.....you lost me.
Illya

[stef]

The Nakina accident was not due to ground icing as pdw stated. It was caused by a combination of less than takeoff power set, a shaky pilot with a miss trimmed aircraft, and a tricky load (plywood.)

[pdw]

You're correct, no evidence of "ground icing " in there .. sorry

[Meatservo]

PDW, It is my theory that you are not a person but are rather one of the NLP programs designed to pass the Turing test (such as Joseph Wiezembaum's ELIZA). "PDW" is simply the acronym for whatever translates into "natural language processing" in the language of whatever country you were programmed in.

Somehow you have managed to escape onto the internet and have become trapped in this forum where you scan for keywords and then ask questions and make comments from a large database.

Is this true or false?

[pdw]

No no ... pdw are simply initials of my name. As for discussing accidents (reports / scenarios) it only had turned into a genuine interest after my own and then noticing on occasion an accident conclusion obviously in need of correction or added info/verification, ... especially when seeing the synopsis are to be used as teaching examples. Learning from the mistakes of others ... or as sidebar would say: LFTMOO ...

[Illya Kuryakin]

You're correct, no evidence of "ground icing " in there .. sorry

I remember the accident. Ground ice was certainly the talk of the time. Just because the TSB a report found "no evidence" doesn't mean there was none. Perhaps it melted?
Illya

[pdw]

Unlikely, as far as any melting, seeing there were similar temps as in this YZF emergency (a suitable comparison in that sense). The ZF evidence is 100% preserved with it being -10C at the surface, so the final report should have all the details about the catch involved with this type of extreme example of liquid precipitation / supercooling.

Yes there were enroute accidents in the past (some ground icing ones too) where 'evidence' is unavailable due to having "melted", thereby rendering those investigation processes inconclusive as far as icing effects qualifying as a potential factor or not.

[Axial Flow]

TSB Report out

CBC News Article

TSB Report


From the weather synopsis in the report: "There was no freezing drizzle in the forecast: since the minimum probability threshold for including a phenomenon such as freezing drizzle in a TAF is 30%, the forecaster evidently expected that the chance of freezing drizzle at CYZF was less than 30%."


Apparently it's not a big deal for a trained meteorologist to interpret all available data and be wrong but hang a pilot for not consulting the 850mb and 700mb charts to determine same.....yes the GFA said a band of patchy mixed to 14000 but I had one in September call for it up to 20,000 feet and there wasn't a drop of ice to be found. When you have such little soundings and 6 24hr METAR's to pull info from I can see why they are hit and miss. Whereas Ontario has US Nexrad to pull from and multiple weather sites to see what's actually going on. Also, half the time satellite imagery is up to a day old or the image is corrupt in the north so maybe start spending some of that deficit money on aviation since we are never going to be able to pay it back anyways.