[atsiii]

I am despondent to start this new thread, but if anything I say here helps you avoid making the same mistake I did… then the effort is worthwhile.

Last Sunday afternoon I ran my 1969 T337D out of gas about 8 minutes out from my home field. I elected to make a "wheels up" forced landing in a cow pasture. There were neither injuries nor damage to property on the ground, but my Skymaster (i.e. my love in life) is badly bent and possibly broken. As I walked around my bird in the field, I kept saying out loud and to myself… “I must have 12 more gallons… where is the gas… I had enough gas… where’s my 12 gallons?” How did this happen?

I have owned and flown my Skymaster for 4+ years, logging in excess of 1000 hours while enroute back and forth to 150+ airports in 35+ states and three countries. I would like to think that I’m pretty comfortable with its performance, limitations, systems, etc. I’d also like to think that I’m a pretty safe and proficient pilot. The truth is, I’m a pretty conservative (i.e. a sissy!) pilot, and very anal when it comes flying, and the taking and keeping of various flight records.

For example, I record the Hobbs at start-up, Hobbs at departure, Hobbs at level, Hobbs at aux, Hobbs back to mains, Hobbs at shutdown, etc. Further, once level, I lean both engines using the lean-find function of my JPI EDM 760, then religiously record which cylinder peaked, the temperature of peak, the target cruise temperature of peak minus 75 degrees, and the GPH fuel flow that results from running at 75 degrees rich of peak.

Because of all this, I am typically able to land and immediately calculate how much fuel I burned (i.e. how many gallons they will put on when they top off the tanks). For example, I might land after a 4-hour leg, figure I burned 98 gallons enroute, and then the FBO would pump on 101 gallons. I would think to myself, “gee, 3 gallons off over 4 hours! Not bad… 3 gallons off over 101 gallons, or a 3% error. Pretty darn close when you consider I still have in excess of an hour of fuel in reserve, or 20% more!” Thus, I have been struggling enormously since last Sunday afternoon, trying desperately to understand just how this could have happened. Well, yesterday afternoon I finally figured it out.

For the last 4+ years and 1000+ hours, my typical flight profile was point-to-point cross-country flying. I would fly 3 or 4 hours, land and top off the tanks, then fly 3 or 4 hours more. My time & burn fuel planning would seemingly always put me within 2 to 4 gallons of the actual gas purchased. So I developed a lot of confidence in the fact that I had 4+ hours of flying in my topped main tanks, and another 1.3 hours in my aux tanks.

The problem, as it turns out, is that I was not off “3 gallons over 4 hours” or “3 gallons over 101 gallons;” I was off because I was underestimating the fuel consumed during start-up, warm-up, taxi and initial departure (i.e. the fuel used before the weight was off my nose wheel squat switch allowing the hobbs to start tracking time). I had developed and was using a value of 6.62 gallons for this phase, but the real number now seems much closer to 10 gallons for my T337D. That was the 3 gallons my calculations were off over the years, and it all had to do with the period before the Hobbs meter started turning. But since my normal flight profile consisted of a 3 or 4-hour cross-country trip between top offs, there was only one cycle (i.e. start-up to rotate segment) per leg, and the 3 gallons was insignificant to the overall flight. Unfortunately, between 6/20 and 6/22, I had four separate start-up and landing cycles all on the same main tanks!

I wanted to attend a friend's wedding at Johnson Creek, Idaho (3U2). However, this is a 3500-foot grass strip in the mountains at 5100 MSL, with a blind S-curve approach to Rw 17 and tall pine trees at both ends. I had never landed my Skymaster on a grass strip; and I was a bit worried about my takeoff roll in long, wet grass. I also knew many of my pilot friends from U59 would be there, so in my typical (sissy!) fashion, I decided to fly over a couple of days and make sure I felt comfortable. I topped off all four tanks on 6/20 (128 usable) and headed over.

It was 1.5 hours over (hobbs), of which I flew 1.2 hours on my aux tanks. I landed, shut down and walked around a bit. What a BEAUTIFUL place to go plane camping! I started up, departed and flew home on the mains, which was 1.7 hours. Thus, when I got home on 6/20, I had put 2 hours on the mains and 1.2 on the aux tanks. I knew I would be heavier with all the camping gear on the 21st, so I elected to top off only my aux tanks. Just as expected, they put 24.6 gallons into the aux tanks (I had flown 1.2 hours at 20.7 GPH). I figured we would depart on the 21st with 1.3 hours of fuel in the aux tanks, and another 2 hours of fuel in the mains, for the 1.5-hour trip over to Johnson Creek.

On the 21st, I purposely flew most of the trip on the aux tanks (the POH requires all takeoffs and landings to be accomplished on the mains). Our time over was again 1.5 hours, of which I flew 1.2 hours on the aux tanks. We pulled .3 hours out of the mains, but .2 of those hours were in descent into 3U2 at 6 to 8 GPH fuel flow. Thus, once we shut down, I estimated we had about 1-¾ hours of fuel remaining in the mains.

As expected, Sunday greeted us with rain and lots of low-lying scud clouds. The weather began to break around noon, and was good VFR by 1pm. We loaded up our gear and departed about 2pm. Thinking (based on time & burn) that we had about 1 ¾ hours of fuel at takeoff, the plan was to climb VFR until we could see the weather to the east, then depending on how much we had to skirt around the clouds, we would land at Challis or Salmon for fuel before heading home. Unfortunately (as it turns out!), when we departed, we were handed a stairway to heaven VFR climb to the east right on up to 13,500, where we leveled off on top of a scattered to broken layer. Once we had leveled, reduced power to about 60% (27”, 2250rpm and 11.5 GPH), the GPS and Loran were both indicating 190kts groundspeed, and that home was only 58 minutes away. Since Challis and Salmon would require dropping down through some VFR holes, and since we were showing only .2 hours into the flight, and since I figured we had 1.75 hours of fuel at takeoff (of which we had used only .2), I reasoned that we could make the 1.0 hour trip home with a ½ hour of fuel in reserve. If the speeds didn’t hold up, we could stop at Idaho Falls or Rexburg. Well, the speeds did hold up, and even increased some. At one point we were 35 minutes into the flight, with only 30 minutes remaining.

About 12 minutes from the airport we started loosing engines to fuel starvation, and by about 8 minutes out, we had burned the last of the aux tanks, tried cross-feeding the mains, and were without any power. I feathered both props and we began looking for a forced landing site.

The Hobbs read 1.2 hours into the flight as we sat in the field. 1.2 hours… when I had departed with 1.75 hours… how could that be? Furthermore, we were out of fuel after only 3.7 hours of flight on the mains… when I had gotten 4+ hours of flying out of the mains since owning the airplane. What was going on?

I kept asking myself… “How do you put 6.5 hours of fuel on board for at most 6 hours of flying, then run out after only 5.7 hours. Well, hopefully my screw-up is now obvious to you all. I had underestimated the start-up to rotate fuel consumption by about 3 gallons. In my normal flying, that didn’t matter much. But in this case, I had 4 separate start-up, takeoff and landing cycles on the same tanks. I was off in my fuel estimate by 3 gallons after the first cycle… 6 after the second… 9 after the third… and 12 gallons (in excess of an hour of cruise!!) by the time I made my in-flight decision to head home on a 1 hour direct flight.

Folks… I don’t need a bunch of pilot jeering to rub salt in my wounds, and to point out everything I did wrong. I’ve probably already done a better job of that than any of you could, as I’ve always been my own worst critic. So please just think about this. All of us fly Cessna’s with worthless fuel gauges, so none of us rely on them. Most of us use one method or another of time & burn fuel planning. Please realize that if your normal flight profile changes, your normal (time proven!) rule of thumb may not apply! Sure, I knew I used more fuel on departure and climb… but I have all those values figured into my method, and I’m dead on with them. I've done the arithmetic, time and again. But I failed to realize I was underestimating the fuel used from start-up to departure rotation. Had I known this was closer to 10 gallons than 7 gallons, my arithmetic would have shown me I was cutting it too close (for a sissy!), and I would have put on more fuel.

I’m not sure what will happen to my beloved Skymaster. I am sure the FAA and NTSB will probably have a field day with me! But I needed to understand what happened, and I needed to share it before someone else made the same mistake. Think about what I did wrong. Think about adding a component to your fuel planning to allow for takeoff cycles. Think about developing graduated dipsticks for your tanks, and then using them before every leg. Nothing else can tell you how much fuel you really have. And think about getting a Totalizer of some sort, if you don’t already have one.

We walked away without a scratch having provided great entertainment for the cows and horses. But my Skymaster did not! Nor did my pride, nor probably my record. Please think about it. Fly safe!

Allen
N86182