Take the example of Engro Pakistan TFCs with tenor of 5 years that have been issued and they have promised to give a fixed interest rate of 14% annually on its investment. If the company goes down within that 5 years, forget the 14% interest, you won't even get your original investment back.
If the company's performance goes down and the company is close to bankruptcy, the TFC values will also go down and hence you may make a loss on principal if you try to get out of it and sell it in secondary market (to avoid the risk of complete loss at the time of bankruptcy). It's just like investing in stock market in Engro shares. If the performance goes down, shares will give you loss. The only difference is that Engro TFCs commit a fixed rate of 14% and their shares do not commit any fix rate of return (the dividends may have a historic average yield of 5%, but that is variable). However both are risky, although the magnitude of riskiness vary. They may launch another TFC with variable rate of KIBOR+3%, just like other companies. In that case even the interest rate isn't fixed. But there will be risk involved if you invest in them.
Similarly they may even issue preference shares with a fixed annual dividend rate of 14%. They are just like loans and investors will only get 14% every year on their investments. This is less risky than common shares but more risky than debt (as dividend payment have less priority than payment of interest).
The point simply is, all the investments, whether fixed, floating, or dividends have risks if you invest in them. The investor will do nothing during that period and will only realize his profit or loss after a year. You can't just call investment in TFC un-islamic and investment in shares islamic by saying one is risky other is relatively less risky.