Saturday, December 1, 2012

Pre-flight fuel calculation

         Three different calculations of fuel quantity information, based on one incorrect information source Investigation 
         In June 2007, a Brasilia turboprop aircraft conducting a charter flight with 31 people on
board lost power from its left engine shortly before landing at its destination. The flight crew conducted a missed approach and landed about 12 minutes later.The fuel tank supplying the left engine had no fuel remaining, and the fuel quantity indicator was over-reading because of a mechanical defect. Other methods of calculating the fuel quantity existed, but were not used effectively.
           • The aircraft was equipped with a fuel totaliser, which would provide an indication of the fuel consumed during a flight, but most of the operator’s flight crew obtained the fuel consumed by calculating the difference between the ‘total fuel quantity at departure’ and the ‘residual’ fuel at the end of the flight. Both of the fuel quantities used for this calculation were initially derived from the fuel quantity indicator, which therefore bypassed the increased reliability that was available by using information from the independent fuel totaliser.
          • The tanks were only rarely filled, which lessened the opportunity to obtain an accurate knowledge of the fuel quantity in the tanks. This is common for charter operations where maximum payload is normally a consideration.
            • The wrong fuel density was used when converting from litres to kilograms of fuel. This conversion was a normal part of fuel management in this aircraft, and produced an inaccuracy of about two per cent.
               • The ‘dripless measuring sticks’ installed on the aircraft were not used to reconcile fuel discrepancies. Instead, discrepancies in the fuel quantity were normally reconciled to the unrecorded fuel used by the auxiliary power unit. Various methods were available to assess fuel quantity on this aircraft, however, the methods had been modified so they were all based on information that was originally derived from the fuel quantity indicator. The undue reliance placed on the accuracy and reliability of the fuel quantity indicating system meant that when the fuel quantity indicating system became faulty, the flight crews were not aware of the potential for
engine fuel starvation. Cross-checking the fuel quantity indicating system with the dripless measuring sticks’ installed on the aircraft before flight would have highlighted the problem. Although there was fuel on board, the factors that contributed to this fuel starvation incident could have quite easily resulted in complete fuel exhaustion.
Lessons learnt
Accurate knowledge of fuel quantity at the start of a flight is essential for any fuel-critical
operation. All subsequent assessments are derived from that initial number. If only one fuel quantity measurement is used, then it is not possible to find out if that system is working properly because you have nothing to compare your information against. Separate, independent fuel quantity cross-checks provide a much more reliable system for knowing how much fuel is being carried at the start of a flight.
Avoidable accident 

Qualty,Safety and Training

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