LESSONS MY COMANCHE TAUGHT ME
FUEL TANK TRAUMA … TOO MANY TANKS
by Ben Ayalon
We bought our Comanche 260-C a week before Christmas 1999 and flew it home to Elstree, England (EGTR) on Christmas Eve. The aircraft went into the shop for a good check-up, and some additions were fitted. When the aircraft was ready, I flew it along with my mechanic who had a Comanche 250. Afterwards, I went through some transition training on the Comanche with a respected instructor who knows Comanches very well.
A few months later on a Saturday in April, my wife and I were on our way to our first Comanche fly-in, being held at Guernsey. This is an island in the English Channel, part of the Channel Islands near the coast of France. It was also to be my first Comanche flight away from the local area. My total time was just under 400 hours with about 18 hours in the Comanche, and out of that, 8 hours were logged as Pilot Under Training; not a great deal of experience in an aircraft with a reputation of being unforgiving of pilot errors.
The 260-C can carry 90 gallons of fuel (86 useable) in four tanks; 15 gallons in each of the auxiliaries and 30 gallons in each of the mains. Flying time was calculated to be 1.5 hours at 140 knots, at a fuel flow of 12 to13 gph. It was a fine day with clear skies; we had enough fuel and there was nothing to be worried about. We had left EGTR with 65 gallons of fuel in the tanks, unevenly distributed.
While EGTR is northeast of London, the shortest route to Gurnsey takes us west to fly around London Heathrow Class "A" airspace before turning south. We took off and climbed to 2,300 feet; power was set at 65%, with fuel flow at 12.5 gph. Following the POH advice and common practice, I used the auxiliary tanks first, leaving the mains for the water crossing and landing. I also followed the clock's long hand; if it is between 12 and 6, a right tank will be used; between 6 and 12 a left tank will be used; and if over water a main tank is used, always.
We reached our coastal departure point near Southampton 35 minutes later. The electric fuel pump was turned on and I changed from aux to main tank. The next 30 minutes was spent flying over the English Channel, one of the world's busiest waters. Upon arrival over Cherbourg on the French coast, I switched back to aux tank. The single fuel gauge was just under one half tank. We had only another 30 minutes or so to go, 15 of them over water for the short crossing from the French coast to Guernsey. We arrived over our coastal departure point, said goodbye to French control, and called Guernsey Approach for instructions. We were cleared to enter their Class "A" airspace, not above 1,500 feet.
I was relaxed and confidant that I knew what was to follow since my Comanche used to live in Guernsey and I had flown there twice before. Guernsey was a few miles away and I had started to enjoy the short water crossing. Suddenly the intercom sprang into life; it was my wife, "Do you always fly the fuel so low?" she asked. "There is no problem," I said, "we have lots of fuel. Don't worry; I changed tanks about 10 minutes ago and we had half a tank. We are fine." " But look!" she insisted. I looked at the gauge in order to keep her happy. "Yeah, it's fine," I said … WHAT? The needle was touching the red line; we were flying on fumes. I turned the electric fuel pump on and changed to mains.
Have I said that over water I always fly on mains?
Our position was some 10 miles east of Guernsey, and it would be another 9 minutes before we landed.
After landing and parking the aircraft, I looked inside the aux tank. It was dry.
How could it happen, you ask?
The single engine aircraft I have flown before had only two tanks; one in each wing, of equal capacities. The Comanche was the first aircraft I had flown with four tanks of different capacities, but only one fuel gauge. The gauge always shows the remaining quantity in the tank that is in use.
After crossing the English Channel and reaching the French coast, I had changed from a main tank to an auxiliary tank. The aux tank was just under half full, with 5 to 6 gallons left. With fuel flow of 12 to 13 gph, our endurance would have been approximately 24 minutes. Flying time from the French coast to Guernsey is approximately 21 minutes.
There is no doubt in my mind that we would have lost the engine on downwind or final with no chance of a restart.
Later, at the hotel, we sat by the pool watching an ICS member playing with his two children in the cold water while I reflected over our fortune.
What had I done wrong? What have I learned?
1. In my mind I had reverted back to a one tank per wing type of aircraft. I continued to fly the aux tank and thought that I had 13 gallons left, one hour's worth, as the gauge was just under one half. (Later, the tank was filled with 13.5 gallons.)
2. I was too relaxed and did not keep a fuel log; this alone could have prevented this incident.
3. My scan of engine and fuel gauges was poor.
When someone tells you something is wrong, always investigate. NEVER ignore it.
Ben Ayalon, born in Israel in 1955, studied aircraft engineering at Holtz Technical College in Tel Aviv. He served for 6 1/2 years in the Israel Air Force and later joined Israeli Aircraft Industries where he took part in the development of the "Lavi" fighter. In 1987, Ben moved to the UK to study and obtain a degree in Business Administration. There, he started his own computer business, and now owns a Comanche 260-C, based at Elstree, England (EGTR).