++safety Alert++

[Jim Smith]

First of all I want to say the subject plane is a one owner for over 40 years, extremely well-maintained and always hangered. I have owned it for about two years and continued with hangering and tip top maintenance. I have a very good understanding of Skymasters and their systems having owned six of them. The plane is flown regularly. It has a Shadin Fuel Flow system that is very accurate. I rarely use my Aux tanks and have never had the need to cross-feed. The plane has had no unusual alterations, modifications, or damage history.

Now here's the story:

Return from a trip with my usual 45 gallons of fuel burned off the main tanks. A visual inspection indicated the burn appeared to be even with 22-23 used per side. Plane sat in my hanger for approximately a week and a half. Last weekend, decided to fly to an airport only 55 miles away. Did a visual inspection and both tanks still showed the same approximate amount (22-23 gals) per side burned from my previous trip so I decided not to top off. I knew my trip for the day will burn 20-23 gallons since I was going to shoot a few approaches on the way over and way back. Upon my return home I did notice the left main fuel gauge was lower than normal. Upon landing I taxied directly to the fuel farm to top off. Ready for this? The left main took 44 gallons (2 short of its 46 gal capacity). 22ish from my previous trip and 22ish from the trip I just took. The right took about 23, the correct amount I burned on that side from my previous trip. The total fill up was about 67 gals, exactly what I burned since last fill up according to the Shadin. What this all means? ALL of the full used from my short trip that day came from the left main. Nothing used from the right. I landed 2 gallons short of a double engine failure, as both engines were obviously using that tank. BOTH fuel selectors had been in their 'normal' respective positions, confirmed during my preflight, my GUMPS checks, and after landing. I know this plane well and have three mechanics very experienced with Skymasters. We are all baffled by this scenario. The plane is grounded and the moment, as we haven't had a chance to tear into it. I would like to get some thoughts and opinions before doing so. I did check the fuel selector handles to ensure they couldn't be installed on the shaft improperly. They are slotted to fit only one way. I pulled the panels to the fuel valves. No leaks or apparent issues and the cables from the selector handles appeared to be intact. This is obviously of great concern and should be to all owners from '65 thru the F ('71) models. With both engines failing simultaneously and both fuel handles in the normal position, I would've had no clue as to why they were really failing and would've made the logical assumption that both tanks were dry. At 2000 feet we all know what the options are, as things start happening really fast.