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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 14th, 2013, 1:07 pm 
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Joined: April 16th, 2003, 1:50 pm
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Location: Toronto
My one fly-in trip was by single Otter from Red lake... didn't realize beforehand that it would be anything other than an onerous expense. Wow was I wrong about that! As an aside, I still don't know how anything can make that much noise and vibration without completely blowing itself up! I'm sure passenger cars used to be like that when they were first invented, but automotive engineers have gradually turned them into mini cocoons of peacefulness (except for road rage, can't do much about that with equations and formulae).

Re the lift, the density of air changes by only a few percent from normal to hot conditions. Is the Otter engineered with absolutely no margin of error there? I'd have thought it would have a factor of 2 in extra lift, ie only a forest fire could keep it down??


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 14th, 2013, 2:29 pm 
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jbishop2112 wrote:
Re the lift, the density of air changes by only a few percent from normal to hot conditions. Is the Otter engineered with absolutely no margin of error there?

I suspect that air density was not the only factor involved, with perhaps several conditions piling up to prevent a take-off.

Love hearing bushplane stories. Keep 'em coming.

Here is the twin we used to fly 3 of us in 2 canoes from Missinipe to Sandfly Lake (Saskatchewan, Churchill River). We had to wait for the fog to clear before we could take off.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 14th, 2013, 2:51 pm 
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Re having to wait for early evening, when the air was cooler and therefore more dense:
We couldn't get off in the afternoon but were able to get off in the early evening. No question in my mind that the few percent made the difference.
We had only a short run to get off the water; I doubt that we were too heavily loaded.
Can't remember what the aircraft was, only that it was neither an Otter or a Beaver. I understand that they are designed for short takeoffs.
Something I hadn't experienced before and haven't experienced since: The pilot bounced the aircraft off the waves, pulling it up before he had enough speed to stay off. We came down again and he pulled it up again. Eventually we got off and stayed off. I was rather concerned that he would damage the struts.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 16th, 2013, 10:31 pm 
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As was stated, in the past the practice was for the pilot to decide about external loads such as canoes, and how they were tied onto the float struts. His choice. And he was motivated to do it very well because he only had one chance -- a canoe coming loose in flight meant game over.

But a few years ago this was rescinded by TC, as I understand it, and now external loads have to be secured to "Approved" racks -- that's a rack which results in a Supplemental Type Certificate. Official. Approved. Stamped.

This ups the cost for the charter operator, which gets passed along to the charterer.

This is one case where a bigger aircraft, such as a Twin-Otter helps, because the canoes can go inside the cabin. Smaller canoes, about 14ft, can fit in a Single-Otter.

Dave


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 16th, 2013, 11:20 pm 
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When did the regulation come in on the 16' max. canoe length load without a rack?
I flew in a single Otter in 2000 (2.5 hr flight) with six people and two canoes on the outside (one 16', one 17') and no racks.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 16th, 2013, 11:32 pm 
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Don't quote me exactly, but it was about 2008.

Can anyone from TC chime in? I'd rather do anything than wade through the TC website...

Dave


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 17th, 2013, 12:34 am 
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Joined: September 29th, 2005, 5:57 pm
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My understanding of the external load issue, based on some decades of northern chartering, panicked perusals of the TC website, and discussions with the operators I have chartered with –

According to the regulations, it was always a requirement that an external load be authorized by a supplemental type certificate (STC). However, a provision existed for an exemption to the STC requirement, if an operator could meet certain conditions set by TC. Conditions varied from time to time- external loads have been controversial for a long time – but included such things as attachment methods, pilot training, maximum weight restrictions, operating conditions, etc.

Finally, after many fits and starts and postponements, the exemption option disappeared. Now an STC is required for any carriage of external loads. According to people who have gone through the STC process, an STC is highly specific to the aircraft and the load. There is not just an STC for a canoe on a Cessna 185, for example. The STC would be specific to the aircraft that went through certification testing – i.e. Cessna 185 F, engine type, float type, STOL package, etc., and load type – canoe, boat, lumber, maximum length and weight, means of attachment, etc.

According to the TC website, there are a considerable number of STCs in existence, mostly for “veteran” aircraft like the Otter and Beaver. If a type certificate exists for your configuration of aircraft and the particular load you want to fly, you are ok – although you may need to purchase the STC. If not, you need to apply for the STC and go through the paperwork and flight testing with TC. This is an expensive and time consuming process. I know that NWAL (Fort Smith) and Air Tindi (Yellowknife) went through this process in the spring of 2011 to get external load certification for their 185s. Things did not happen quickly after that. NWAL was given a temporary STC for their 185 for the summer of 2011 at the last minute – I was actually sitting in the plane when it arrived, and we got out and tied on the canoe. Tindi faced similar delays in getting a response from TC, but finally got what I believe was a similar temporary STC (and were able to fly Hoop in for his trip that summer.)

I’m not sure how the Tindi situation would have been in 2012 – they sold off their 185s in the spring of 2012, and did not operate them that summer. NWAL was apparently told that based on their testing, they would not be given an STC for the 185. However, after they made further inquiries, it was determined that they did meet the requirements for the STC, and now have an external load certification for that aircraft. It arrived too late for my trip planning last summer, but according to the local canoe trip outfitter, they were able to fly external loads (and passengers) by mid-July last year.

A troublesome trend for larger groups – driven, I am told, by insurance considerations and not specifically TC regulations – is that more operators are now refusing to fly canoes and passengers in the DHC-6 Twin Otter because the stacked canoes block one of the rear exits, which could be problematic if an emergency evacuation is required. I know Tindi would not fly canoes and passengers out of Yellowknife in their twins (last summer) and a friend had a similar response from Osprey Wings in Missinipe, Saskatchewan for his trip last fall. Planning fly-in trips is no longer simple (depending on where you want to fly from and the type of aircraft you require): maybe we should all buy Pakboat shares.

Regulations and bureaucracy can be frustrating, but I’m not sure what the answer is. A sobering example of what can happen when pilots don’t pay attention to the rules (or use common sense) can be found here:

http://www.tsb.gc.ca/eng/rapports-repor ... 0q0117.asp

An acquaintance of mine died in the front right seat of this Beaver, 1000 pounds overweight, in northern Quebec.

-jmc


Last edited by jmc on January 17th, 2013, 1:51 pm, edited 3 times in total.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 17th, 2013, 1:01 am 
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What's the situation with helicopters? In the 60's & 70's my brother worked in the NWT, at that time they used Otters (single and twin) or Beaver, he went back to do some follow up work in the late 90's and at that time it was 100% chopper.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 17th, 2013, 1:04 am 
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A great post. Very informative. Thanks.

Dave


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 17th, 2013, 1:38 pm 
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jmc post is as I understand it and as I have experienced it.

I have seem pilots not allowing a canoe to block an exit but allow a fuel drum to block an exit.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 17th, 2013, 2:26 pm 
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Joined: February 24th, 2002, 7:00 pm
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Location: HFX, Nova Scotia canada
I watched a 185 from a carrier I will not name make three attempts at take off from the back bay in Yellowknife. After each of the first two attempts they taxied back to the dock, removed gear, went back out. Third attempt was successful with the longest run down the bay I had ever seen a 185 make loaded. Had to make the second trip anyway.
Looks like will have to buy Pak boats for northern trips......


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 23rd, 2013, 4:03 pm 
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A not so good breaking story regarding the Twin Otter: http://www.cbc.ca/news/world/story/2013 ... earch.html

I hope it has a happy ending for those involved.

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 24th, 2013, 6:25 pm 
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scoops wrote:
Looks like will have to buy Pak boats for northern trips......


Not so. There are carriers that follow the rules and have the required STC's. It is a lot of paperwork and expensive. But ensuring you have approved racks and paper work is just good business IMHO.

Lots of carriers across the north have approvals so its still possible to work with a reputable company that will fly canoes.

Harlan

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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 26th, 2013, 10:57 am 
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Beverly Lake. Tragically one of Arctic Sunwest's Twins went down last year ( I think) Not sure if it was this one or not.


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 Post subject: Re: The DHC-6 Twin Otter
PostPosted: January 28th, 2013, 1:53 pm 
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Thank you everyone for the great comments!

And yes, you caught my error. The DHC-3 Otter was originally fitted with a Pratt & Whitney Wasp R-1340 (9 cylinder radial) rated for 600 hp. This was P&W's very first engine, and would have been assembled in Hartford, but was eventually overhauled in Montreal.

The current Viking Air version of the DHC-6 is all-Canadian with two PT6-34s rated for 750 hp. (Of course parts come from the world over.)

A warmer day also places limitations on the engines which cannot produce as much power, thus increasing the field length required to reach takeoff speed. I would say the bouncing is to maintain airspeed while removing the drag from the floats by keeping them out of the water.

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