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07/09/2005
   
Tuninter ATR 72 accident: the safety Recommendations addressed to European Aviation Safety Agency - EASA
   
While the technical investigation over the accident occurred on the 6th of August to an ATR 72, registration marks TS-LBB operated by Tuninter Airline, is still in progress, the ANSV has addressed two Safety Recommendations to the EASA, for safety prevention purposes and, for information, to the Italian CAA, Ente nazionale per l’aviazione civile – ENAC.

The aircraft technical documentation available at this stage of the investigation and the wreckage examination showed that the Fuel Quantity Indicator (FQI) installed in the cockpit of the ATR-72 registration mark TS-LBB was a equipment designed for an ATR-42 model aircraft.

The FQI provides the crew with the fuel quantity indication (weight) contained in each wing tank. The normal operation of the FQI is to processes the signal coming from the capacitance probes installed in the tanks with an algorithm typical for each aircraft, depending on tank shape, size and number of probes installed.

The wing tanks of the ATR-72 and ATR-42 differ in terms of max fuel capacity and shape; as a consequence the FQIs for the ATR-72 and for the ATR-42 are not interchangeable because they utilize different algorithms to process the input capacitance signals coming from the tank sensors.
Nevertheless the FQIs for the ATR-72 and ATR-42 have the same dimensions and installation interface; this means that an FQI for the ATR-42 could erroneously be installed on a ATR-72 model and viceversa. The only visible difference between the two FQI is the indication of the max fuel quantity (weight) per tank.

ANSV conducted extensive refuelling tests in order to quantify and assess the effect of an erroneous FQI installation in terms of fuel quantity indication. More specifically, for a given fuel quantity in the tanks of an ATR-72, the FQI readings have been recorded. when an ATR-72 FQI equipment and an ATR-42 FQI equipment were installed.
Results showed that when a FQI equipment for the ATR-42 is installed on a ATR-72 the resulting fuel quantity reading is higher than the quantity contained in the tank.

Based on the above considerations ANSV recommended that the European Aviation Safety Agency, should require an ATR-72 and ATR-42 fleet inspection in order to verify the installation of the applicable Fuel Quantity Indicator, and should consider the possibility to mandate a modification of the Fuel Quantity Indicator installation in order to prevent any incorrect fitting.
   
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