So, the other day (back in early March) I’m having coffee with my friend Adam, who is planning to fly his A36 Bonanza around the world later this spring and is in the late stage of flight planning, which feels a lot like the initial stage. We meet for coffee one morning every week or two to compare notes, which mostly means that I listen to his latest exorbitantly expensive purchase or plan or aircraft modification.
In the midst of talk of visas and crew identification cards and avgas availability and HF radios and PLBs and whether or not a life raft needs to be TSO’d or needs to have a double floor or a single floor, we were talking about the so-called “Dolly Parton” 120-gallon tip tanks he is installing for the trip, notably for the long overwater legs. The dilemma is whether to set them up with a direct-feed system, which would be an extensive modification of the fuel system, or whether to remain with his present feed system, which requires pumps to transfer fuel from the tips to the main wing tanks. What happens if one or both of those pumps fails over the ocean? Should we install backup fuel pumps to stand in should the main pumps fail? How often do they fail? Do they fail without warning? If one fails will the valve fail open or closed? Would backup pumps simply add complexity to the electricals, the pumps, and the fuel lines and thus introduce multiple points of failure? Unknowable, but worth considering.
So we are analyzing our strategies if a pump failed in a single-pump system. Those are huge tanks holding nearly five hundred pounds of fuel at the recommended level of 80 gallons way out on the wing with a long arm and thus creating a serious imbalance. Apparently no one has ever landed a Bonanza with more than a 20-gallon imbalance in those tanks. We are thinking that would probably apply equally to ditching. So we are speculating as to what we might do should a pump fail and we have fuel in one wing tank that we cannot get to nor dump. (General aviation airplanes, unlike airliner jets, have no provision for dumping fuel because most light general aviation airplanes are not limited to a landing weight less than their takeoff weight.)
So, I’m thinking out loud. “We have to burn down the mains to about 25 gallons before we can even begin to transfer from the tips, so now we are burning down both main tanks simultaneously ….”
And Adam interrupts, “George, we are burning fuel from only one tank at a time, remember?”
“But why wouldn’t we be using 12 gallons per hour from each tank?”
“We would be feeding the engine from only one tank at a time.”
“Wait a minute, THE engine? You didn’t tell me. We have only one engine? Are you kidding me? Adam, I think I’ve discovered the fatal flaw in your entire plan!”
Next week we go to somewhere in Alabama for water survival training.