Despite previous posts all my light aircraft failures gave some warning
This is a good point. Aircraft and engines usually talk to you before they give up the ghost. Not only are most engine failures partial power failures, most of them are detectable early on in the process. Many complete failures are fuel exhaustion or fuel starvation (there's a difference) faults...most of the time entirely preventable. Fouled plugs that cause power loss are often the result of improperly adjusted mixtures, improperly maintained magnetos, or even spark plugs. Failure to adjust the idle mixture as a maintenance function leads to overly rich operation on the ground, and sometimes failures after takeoff.
I was assigned a Cherokee 180 to inspect, and found some binding in the flight controls. The group of owners flying it had merely accepted to problem without comment. When I inspected behind the instrument panel I found that the flgiht controls were binding on a wiring bundle and some of the instrument hoses; I was able with little effort to duplicate a condition that would have prevented use of the flight controls in flight. Something which gave plenty of warning, but would have proven fatal at some future date...the owners felt it, recognized the resistance, but elected to do nothing.
How many pilots, low on fuel, press on by overflying airports that have a nice long, hard, available runway with plenty of fuel...in favor of going just a little bit farther? More than a few. I checked out two pilots in a Cessna 210 with long range fuel tanks, and cautioned them both that filling the tanks to the bottom of the filler neck made the tanks look full, but left them one hour of fuel short on each side. Both pilots failed to heed that counsel and each ran out of fuel at a later date in a 210 with long range tanks...and made an off field landing.
During a spring training fire school put on by the government several years ago, I was returning from a field exercise in a PZL Dromader (single engine, low wing, tailwheel) equipped with a PT6A-45R engine. I was transiting a very large valley, and about ten miles from the airport I detected a faint smell of smoke. At the time I wondered how a fire in such a vast area with wind, would be concentrated enough to be detectable in the cockpit. I'm used to smelling smoke in the cockpit during large, active fires...but this was a simulated fire, and it was downwind. As I got closer to the airport, the smell got stronger. I did an overhead approach to the runway, and as I crossed over the numbers at a thousand feet, the cockpit began to fill with smoke. As I crossed the threshold during landing it was becoming hard to see and my eyes were burning. I vented the cockpit as I roled out, and breathed through an opening in one canopy door.
As I cleared the runway the cockpit became thick with smoke, and shortly thereafter the brakes (and as a consequence steering) failed. I had a fire on board, with a newly installed dual electrical hydraulic pump. A pressure switch which was supposed to cylce the pump on and off had failed, allowing the pump to run continuously, and the pump burned up...and caught fire. I was able to exit the airplane, remove a side panel which covered the pump, and put out the fire.
Had I been closely monitoring the electrical load, I'd have seen the pump running by a higher amperage output; it would have given me a clue...it would have been detectable. This wasn't an engine in this particular case, it was an onboard fire. However, I'd flown this airplane for several years previously, and it had used an engine driven hydraulic pump...no reason to monitor that ammeter that closely. The pump was a brand new installation, this was my first flight with the new system. This underscores several points, starting with knowing one's specific airplane, intimately. Another is one previously made; airplanes and systems talk to you. Sometimes that very little, nearly imperceptible voice, is all the warning you get. A third addresses the following quote:
Which do people think is more important...going for the best field or picking a worse one that is much closer so you can do a circuit around it?
You have only one priority; getting down safely. Flying a traffic pattern is a nice extra, but you don't often get to choose a real emergency; it chooses you. Consequently, you don't always get to choose the chance to fly a pattern, and you won't always have the altitude or opportunity to do it. In the latter case described above, had the situation become more developed and manifest itself earlier, I wouldn't have flown the overhead aproach, but would have entered straight in. Had it occured away from the airport, I'd have put it down on the high desert floor, or a road if one was available.
Don't give up a good landing site in favor of trying to fly a pattern. Flying a pattern sometimes makes landing a little easier, but the pattern isn't the thing. The safe landing is. Don't lose sight of the goal.