What are the most significant risks to life for the airline passenger?
Risks of dying of air travel are tiny. We can find data on direct risks of air travel, and there is an app for calculating how many years of continuous flying would lead to known aviation related chance of dying. Tiny.



Some risks ore harder to quantify though. If you fly economy class, you may be exposing yourself to the health risk of excessive sitting. It damages blood vessels and may lead to Deep Vein Thrombosis which can cause sudden death. From this news article of 23 Oct 2000:


  Emma Christoffersen, 28, died from deep vein thrombosis (DVT) believed
  to have been caused by sitting for several hours on the 12,000-mile
  flight to Heathrow from Sydney. Medical experts said she was one of
  the youngest victims of DVT, a sudden illness caused by lack of
  movement over a sustained period that claims the lives of a number of
  airline passengers each year.


Also, you're excluding the effects of airline food. An economy class meal costs between USD 2.- and 10.-, how good is that for someone to eat day in day out?

Air travel is not an activity that is good for health if undertaken on a daily basis. During a long economy class flight people should get up for a brief stroll every few hours or so, and once landed should be vigorously walking around in the sunshine over the course of a couple of days to reset their blood flow and health before taking another flight. Like pilots do.

From Mayoclinic.org:


  One study compared adults who spent less than two hours a day in front
  of the TV or other screen-based entertainment with those who logged
  more than four hours a day of recreational screen time. Those with
  greater screen time had:
  
  
  A nearly 50 percent increased risk of death from any cause
  About a 125 percent increased risk of events associated with cardiovascular disease, such as chest pain (angina) or heart attack
  


Air travel is very safe and mortality rates are low, as illustrated in this article from The Economist. It is a good thing though that most of us only take a couple of flights a year, with ample time in between flights. But it's not only economy class travel that is bad for health. I know people who used to be up in the air on an almost daily basis for years, flying business and first class. Unfortunately one of them is not here anymore, most probably due to DVT.