Crashed Tuninter ATR had wrong fuel gauge installed

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Italian investigators are urging ATR operators to check fuel gauges on their aircraft after discovering the Tuninter ATR 72 lost in a fatal accident off Sicily last month was fitted with a fuel-quantity indicator meant only for ATR 42s.

Investigation body Agenzia Nazionale per la Sicurezza del Volo (ANSV) states that examination of the wreckage from the crashed aircraft – which ditched north of Palermo on 6 August after suffering a dual engine failure – plus the study of documentation shows that an incorrect instrument had been installed.

While ANSV stresses that the investigation is continuing, it has issued two emergency recommendations to the European Aviation Safety Agency (EASA) and Italian civil aviation authority Ente Nazionale per l’Aviazione Civile (ENAC) following the discovery.

One recommendation urges operators to check that their ATR 42s and 72s have the appropriate fuel gauges installed, while the second suggests that a modification be introduced making it impossible to fit the wrong gauge to either aircraft type.

ANSV says that the fuel-quantity indicators for the ATR 42 and 72 are physically similar and that it is possible to fit the wrong gauge to either’s instrument panel. But differences in the internal algorithms mean that the wrong gauge would not register the correct quantity of fuel on board.

“Tests have shown that if a fuel-quantity indicator meant for an ATR 42 is installed on an ATR 72, the cockpit display shows a fuel level greater than that which is actually present,” says ANSV, which has performed several experiments on an ATR 72 to assess the effects of interchanging the instruments.

ATR 72 aircraft have a total fuel capacity of 5,000kg compared with 4,500kg for the smaller ATR 42.

Sixteen of the 39 occupants on board the Tuninter service between Bari and Djerba died as the aircraft attempted an emergency landing at Palermo.

In a message to all operators of the turboprops, ATR says that a shortage of fuel is among the possible causes of the accident. It says that the manner in which the central fuselage and wing sections continued to float after the crash, plus the lack of fuel traces at the crash site, support a fuel-exhaustion scenario.

“The reported value of the fuel indication at the time of the double engine flame-out supports the hypothesis of a potential inappropriate…installation of a fuel-quantity indicator on the ATR 72 aircraft concerned,” says the manufacturer. “This configuration could imply an over-estimated fuel quantity indication.” 

Its all-operator message also states: “ATR reminds operators to strictly comply with existing aircraft maintenance manual requirements.”

A spokesman for ATR says that the company believes that its maintenance manuals for the type are “clear enough” in detailing the need for operators to install only specifically-listed items during overhaul work.

He says that the fuel-exhaustion theory remains “one of the different hypotheses” under study by the Italian investigators and that it is too early to say how ATR will respond to recommendations to prevent inadvertent incorrect installation of the fuel gauges.

ATR says that the investigation is still progressing and that the analysis of the cockpit-voice recorder and flight-data recorder from the aircraft should provide much more information on the issue. EASA has yet to respond formally to the Italian recommendations.