Narrative:

While enroute I switched from inboard tanks indicating 1/2 full to outboard tanks indicating 1/4 full. After burning the outboard tanks; I switched back to the inboards and the right engine surged as if experiencing fuel starvation. I immediately switched the right fuel selector back to the outboard tank and diverted. At the time of the occurrence; the right inboard tank indicated 1/2 full; the right outboard tank indicated 1/8 full; the left inboard tank 1/2 full and the outboard tank 1/8. I used correct procedure and checklists while switching tanks. Due to the fuel quantity indications I thought I was experiencing a failure of the fuel selector when I attempted two more times to go from the right outboard to right inboard and the engine would surge and I would see a fuel flow low annunciator and associated indications of fuel starvation. I left the right selector in the outboard position (as this was the only position the engine would continue to run in and decided against attempting to cross feed as I didn't know the extent of the problem suspected in the fuel selector) and continued to divert to the nearest suitable airport. I made a safe landing at the diversion airport. I spoke with an a&P and found out that the two tanks have 2 fuel quantity sensors; one measures the top 1/2 and the other measures the bottom 1/2. As I understand it now; if the bottom sensor fails; the fuel quantity gauge displays the lowest reading of the 1/2 sensor. In other words; the right inboard tank would indicate 1/2 full at any fuel quantity of 1/2 full to empty. I discovered this to be true as I refilled the tanks in incrementing of 10 gallons -- the quantity gauge was at 1/2 until filled above 1/2 full. I think it would be better if a failure of either sensor would cause a default indication of 'empty' for safety reasons. Contributing factors were the heavy passenger load and the last minute addition of a passenger who weighed in excess of 300 pounds. Also; the passengers arrived early and I felt pressured to hurry my planning. With the right inboard indication slightly higher than the left inboard; I adjusted my fuel order on the previous 2 legs with a mindset that the left side was consuming more fuel and that I had to be careful of the weight added to the excessive passenger weight. While fueling the aircraft; on visual inspection of the tanks; fuel can not be seen in the tanks when they are at 1/2 full or less. That paired with a fuel indication I rationalized was normal with a small fuel burn imbalance compounded over 2 legs and my hurry to accommodate the passengers. I did not perceive the erroneous fuel quantity indication in the right inboard; worse yet; I fueled thinking I had more on board than was there. The weather also contributed to the situation -- the severe clear VMC weather during the day; and the stronger than forecast headwind. I allowed myself to hurry and accommodate a last minute change by the passengers -- with the thought; 'it's VMC; it'll be ok;' and the headwind decreased my planned range. Factors affecting my performance were: fatigue -- the 2 nights previous to the 2 leg flight were in a hotel and I slept restlessly. Eagerness to please the customer; hurrying planning; trading extra fuel for an extra passenger and an eagerness to get home myself. Invulnerability knowing the plane is very well maintained and I didn't assume a failure of the fuel quantity sensor. My low fuel quantity diversion was caused by inadequate fueling and the decisions and judgments leading to this situation were largely influenced by the erroneous 1/2 indication of the right inboard fuel tank; and to a lesser extent the factors detailed above. The corrective actions taken are the replacement of the fuel quantity sensors on the aircraft and my increased vigilance regarding fuel weight and balance issues as a function of time.

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Original NASA ASRS Text

Title: PA-31 pilot experienced symptoms of fuel starvation when switching from outboard to inboard tanks and returned the fuel selector to the outboard tank on the right side then diverted.

Narrative: While enroute I switched from inboard tanks indicating 1/2 full to outboard tanks indicating 1/4 full. After burning the outboard tanks; I switched back to the inboards and the right engine surged as if experiencing fuel starvation. I immediately switched the right fuel selector back to the outboard tank and diverted. At the time of the occurrence; the right inboard tank indicated 1/2 full; the right outboard tank indicated 1/8 full; the left inboard tank 1/2 full and the outboard tank 1/8. I used correct procedure and checklists while switching tanks. Due to the fuel quantity indications I thought I was experiencing a failure of the fuel selector when I attempted two more times to go from the right outboard to right inboard and the engine would surge and I would see a Fuel Flow Low annunciator and associated indications of fuel starvation. I left the right selector in the outboard position (as this was the only position the engine would continue to run in and decided against attempting to cross feed as I didn't know the extent of the problem suspected in the fuel selector) and continued to divert to the nearest suitable airport. I made a safe landing at the diversion airport. I spoke with an A&P and found out that the two tanks have 2 fuel quantity sensors; one measures the top 1/2 and the other measures the bottom 1/2. As I understand it now; if the bottom sensor fails; the fuel quantity gauge displays the lowest reading of the 1/2 sensor. In other words; the right inboard tank would indicate 1/2 full at any fuel quantity of 1/2 full to empty. I discovered this to be true as I refilled the tanks in incrementing of 10 gallons -- the quantity gauge was at 1/2 until filled above 1/2 full. I think it would be better if a failure of either sensor would cause a default indication of 'empty' for safety reasons. Contributing factors were the heavy passenger load and the last minute addition of a passenger who weighed in excess of 300 LBS. Also; the passengers arrived early and I felt pressured to hurry my planning. With the right inboard indication slightly higher than the left inboard; I adjusted my fuel order on the previous 2 legs with a mindset that the left side was consuming more fuel and that I had to be careful of the weight added to the excessive passenger weight. While fueling the aircraft; on visual inspection of the tanks; fuel can NOT be seen in the tanks when they are at 1/2 full or less. That paired with a fuel indication I rationalized was normal with a small fuel burn imbalance compounded over 2 legs and my hurry to accommodate the passengers. I did not perceive the erroneous fuel quantity indication in the right inboard; worse yet; I fueled thinking I had more on board than was there. The weather also contributed to the situation -- the severe clear VMC weather during the day; and the stronger than forecast headwind. I allowed myself to hurry and accommodate a last minute change by the passengers -- with the thought; 'it's VMC; it'll be ok;' and the headwind decreased my planned range. Factors affecting my performance were: fatigue -- the 2 nights previous to the 2 leg flight were in a hotel and I slept restlessly. Eagerness to please the customer; hurrying planning; trading extra fuel for an extra passenger and an eagerness to get home myself. Invulnerability knowing the plane is very well maintained and I didn't assume a failure of the fuel quantity sensor. My low fuel quantity diversion was caused by inadequate fueling and the decisions and judgments leading to this situation were largely influenced by the erroneous 1/2 indication of the right inboard fuel tank; and to a lesser extent the factors detailed above. The corrective actions taken are the replacement of the fuel quantity sensors on the aircraft and my increased vigilance regarding fuel weight and balance issues as a function of time.

Data retrieved from NASA's ASRS site as of April 2012 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.