gyropilot
04-26-2004, 03:29 PM
It's always a good idea to make aircraft systems "idiot proof."
Here's why:
I recently modified my GyroBee with a 10 gallon polyethylene tank. The fuel tank is easily removed from the airframe for fueling, and to simplify the process, I use Acetal quick-disconnect valved fittings in the 1/4" fuel and vent lines. The valved fittings prevent fuel from running out of the tank and airframe fuel lines when disconnected. The tank cap is fitted with a vent line routed to a point on the airframe lower than the tank to prevent fuel spillage in the event of a rollover. From experience, this arrangement works very well! The tank also features a capacitive fuel level probe which has a quick disconnect fitting.
Yesterday morning after I filled up the tank, I installed it on the airframe and connected both the fuel line and the fuel probe harness. But somehow in the process of installing the tank, I forgot to connect the tank vent line! I don't know if I was distracted (there was another pilot from the next hanger over visiting around that time) or I just plain forgot.
None the wiser to my little oversight, I finished my flight preparations, donned my helmet, started the engine, and departed on a 43 SM cross country flight. Everything was going just perfect on this flight. It was a rare beautiful sunny day here in the Pacific NW... 60 deg. F OAT. I was cruising at 700' AGL at a leisurely 50 mph airspeed and the dual-carb Rotax 503 was loafing along at only 5,500 rpm. I later discovered fuel burn averaged only 3.2 gph... usually it's over 4 gph.
About 10-15 minutes into the flight I thought it strange that my fuel level gauge hadn't budged off the full mark. Usually it'll start to move after 10 or 15 minutes of flying. I began to think something must be wrong with the sender or maybe the gauge. No matter I thought... with 10 gallons of fuel on board, I knew I had plenty of fuel to make it to my destination... probably double what I needed.
Now if I loosen my shoulder straps and *really* twist around in my seat while flying, I can look over my left shoulder and barely see the fuel tank. About 15 minutes into the flight I did this and the tank look nearly full! I thought this very strange and figured it must either be an illusion (it's very hard to see the tank) or I must be getting some absolutely incredible fuel economy! Not to worry though... plenty of fuel.
Every 10 minutes or so during the flight I'd glance back at the tank and swear it still looked full, but I knew this was impossible. On the way to my destination I flew over another gyro friend's private strip and hanger and made a couple of low passes to see if he was home. During these orbits around his property, I flew over a wicked looking little valley filled with dense trees... scary place to have an engine failure I thought.
After failing to rouse anyone's attention at the private airstrip, I proceeded on to my destination, still baffled, but not too concerned about the weird fuel situation. I made a nice zero ground roll landing into a 15 mph wind coming straight down the runway at the destination airport. I taxied to transient parking, shut down with 1.2 hours logged, and proceeded to secure the gyro. A couple of pilots who'd seen me arrive, began walking toward me. I pulled off my helmet and started to walk around the back of my gyro, and that's when I saw the sight that sent a cold chill up my spine...
It looked at though a giant Food-Saver had vacuumed-sealed my tank! The tank was indeed full... just with severely reduced capacity! The sides and top were partially collapsed, the tie down straps were loose, and the reason for it hit me like a lightening bolt. I WAS AN IDIOT! There was the short cap vent line disconnected and pointing straight in the air.
I quickly connected the valved vent lines expecting the tank to suck in a bunch of air and pop back into it's proper shape... not a chance... it just sat there looking like a raison. To add insult to my stupidity, the two pilots were approaching... surely they would notice and ask what the problem was. They arrived and asked the usual gyro questions... me feeling queasy as I wondered how much longer the engine would have ran before it quit from fuel starvation. Thank God that Rotax fuel pump is so damn strong!
I was spared the embarrassment of having to explain my partially collapsed fuel tank to the two pilots... they never noticed. After they departed, I blew into the end of the vent line and the tank quickly popped back into its correct shape. I could then see I'd used about 4 gallons out of the 10. I vowed to myself to start using a preflight checklist and to replace the valved vent line quick-disconnects with non-valved versions (which allow air in even when not connected).
They say incidents or accidents are usually the result of a chain of mistakes and poor decisions. In hind sight, here are a few of mine which I feel contributed to this situation:
1. Failure to make the fuel vent line connection idiot proof in the first place.
2. Not using a preflight checklist.
3. Possibly allowing myself to get distracted by visitors when preparing to fly.
4. Shrugging off an obvious fuel level problem once discovered. I probably flew over a half dozen or more suitable airstrips along my path where I could have easily landed and investigated the problem.
Have I learned a lesson again? You bet!
Here's why:
I recently modified my GyroBee with a 10 gallon polyethylene tank. The fuel tank is easily removed from the airframe for fueling, and to simplify the process, I use Acetal quick-disconnect valved fittings in the 1/4" fuel and vent lines. The valved fittings prevent fuel from running out of the tank and airframe fuel lines when disconnected. The tank cap is fitted with a vent line routed to a point on the airframe lower than the tank to prevent fuel spillage in the event of a rollover. From experience, this arrangement works very well! The tank also features a capacitive fuel level probe which has a quick disconnect fitting.
Yesterday morning after I filled up the tank, I installed it on the airframe and connected both the fuel line and the fuel probe harness. But somehow in the process of installing the tank, I forgot to connect the tank vent line! I don't know if I was distracted (there was another pilot from the next hanger over visiting around that time) or I just plain forgot.
None the wiser to my little oversight, I finished my flight preparations, donned my helmet, started the engine, and departed on a 43 SM cross country flight. Everything was going just perfect on this flight. It was a rare beautiful sunny day here in the Pacific NW... 60 deg. F OAT. I was cruising at 700' AGL at a leisurely 50 mph airspeed and the dual-carb Rotax 503 was loafing along at only 5,500 rpm. I later discovered fuel burn averaged only 3.2 gph... usually it's over 4 gph.
About 10-15 minutes into the flight I thought it strange that my fuel level gauge hadn't budged off the full mark. Usually it'll start to move after 10 or 15 minutes of flying. I began to think something must be wrong with the sender or maybe the gauge. No matter I thought... with 10 gallons of fuel on board, I knew I had plenty of fuel to make it to my destination... probably double what I needed.
Now if I loosen my shoulder straps and *really* twist around in my seat while flying, I can look over my left shoulder and barely see the fuel tank. About 15 minutes into the flight I did this and the tank look nearly full! I thought this very strange and figured it must either be an illusion (it's very hard to see the tank) or I must be getting some absolutely incredible fuel economy! Not to worry though... plenty of fuel.
Every 10 minutes or so during the flight I'd glance back at the tank and swear it still looked full, but I knew this was impossible. On the way to my destination I flew over another gyro friend's private strip and hanger and made a couple of low passes to see if he was home. During these orbits around his property, I flew over a wicked looking little valley filled with dense trees... scary place to have an engine failure I thought.
After failing to rouse anyone's attention at the private airstrip, I proceeded on to my destination, still baffled, but not too concerned about the weird fuel situation. I made a nice zero ground roll landing into a 15 mph wind coming straight down the runway at the destination airport. I taxied to transient parking, shut down with 1.2 hours logged, and proceeded to secure the gyro. A couple of pilots who'd seen me arrive, began walking toward me. I pulled off my helmet and started to walk around the back of my gyro, and that's when I saw the sight that sent a cold chill up my spine...
It looked at though a giant Food-Saver had vacuumed-sealed my tank! The tank was indeed full... just with severely reduced capacity! The sides and top were partially collapsed, the tie down straps were loose, and the reason for it hit me like a lightening bolt. I WAS AN IDIOT! There was the short cap vent line disconnected and pointing straight in the air.
I quickly connected the valved vent lines expecting the tank to suck in a bunch of air and pop back into it's proper shape... not a chance... it just sat there looking like a raison. To add insult to my stupidity, the two pilots were approaching... surely they would notice and ask what the problem was. They arrived and asked the usual gyro questions... me feeling queasy as I wondered how much longer the engine would have ran before it quit from fuel starvation. Thank God that Rotax fuel pump is so damn strong!
I was spared the embarrassment of having to explain my partially collapsed fuel tank to the two pilots... they never noticed. After they departed, I blew into the end of the vent line and the tank quickly popped back into its correct shape. I could then see I'd used about 4 gallons out of the 10. I vowed to myself to start using a preflight checklist and to replace the valved vent line quick-disconnects with non-valved versions (which allow air in even when not connected).
They say incidents or accidents are usually the result of a chain of mistakes and poor decisions. In hind sight, here are a few of mine which I feel contributed to this situation:
1. Failure to make the fuel vent line connection idiot proof in the first place.
2. Not using a preflight checklist.
3. Possibly allowing myself to get distracted by visitors when preparing to fly.
4. Shrugging off an obvious fuel level problem once discovered. I probably flew over a half dozen or more suitable airstrips along my path where I could have easily landed and investigated the problem.
Have I learned a lesson again? You bet!