I'm a long-time resident of the BC coast. I avoid travel by small plane in the winter for two reasons:
- Unpredictable weather means that any leg on a small plane is unreliable.
- Flying in small planes in BC is not worth the risk to my life.
I took a look at Ketchikan weather averages, the terrain, and airport facilities. They are fairly similar to parts of the south coast of BC where my rule of thumb is 1 in 5 chance of cancellation during the winter. I would guess Ketchikan odds are similar. There's also a good chance that your plane will fly even if the weather is terrible. That would mean you'd make your connection albeit with a significant increased risk of death. That practice is common on this coast.
BC Weather and Small Planes
The main challenge for small planes operating in BC is visibility. Planes below a certain size aren't able to land safely in limited visibility. There are many regional airports and aircraft operated in BC that seem to be equipped to do some kind of instrument landing. My guess is KTN is so equipped but I'm fairly certain neither Stewart nor the planes that fly there are. This means that if visibility might become limited you probably shouldn't be flying in that plane.
The Vicious Roundtrip Dynamic
Suppose there is a harbour-to-harbour small-plane flight that is scheduled to leave Vancouver at 1030h for Comox and return to Vancouver at 1300h. At around 1015h the pilot has to predict if the weather will be good enough for the whole 2.5 hours to safely operate and land his plane. Visibility is generally not good in this part of the world in winter. Nor is it easy to predict. Pilots at smaller airlines often need flying hours both to pay rent and to advance their careers. The propensity is for a pilot to be optimistic about the weather. Suppose the plane lands in Comox and the weather has worsened. The pilot doesn't live there. There may not even be a safe spot to park the plane in bad weather. And the passengers in Comox all want to get to Vancouver. At that point there is enormous personal, business, and social pressure for the pilot to fly back to Vancouver regardless of the weather. Under that pressure a decision not to fly is unlikely even if weather has terribly deteriorated.
I have witnessed this vicious dynamic all over the BC coast. I don't see why it would be any different in Ketchikan, Hyder, and Stewart.
Small Planes Crash in BC Regularly
In the past 10 years 3 acquaintances of mine have died in small plane crashes and another two narrowly escaped with their lives in two separate crashes. I know first-hand of another three small-plane crashes that claimed another 12 or so lives. 4 of those 5 flights were commercial. Crashes seem to be so frequent that they are uninteresting. Like car accidents. I don't think they all make news but you can find reports of numerous recent plane crashes in BC.
This account is anecdotal. I haven't found any statistics about small-plane safety in BC in particular. There are, however, statistics about small planes in general. There is a good review of those statistics and how to understand them over on aviation.SE. After I read the answers by Geoff Dalgas and Voretaq7 I reflected on the BC weather and terrain and my encounters with small-plane pilots in BC. For me, at least, the conclusion was clear: Flying in small planes in BC is not worth the risk to my life.