The Weekly Reflektion 21/2022

A simple ‘human error’ can lead to fatal consequences. Sometimes a simple solution could have prevented the human making that error and the pain and misery of lost loved ones could have been avoided.

Do you design your systems to prevent the inevitable mistakes that people will eventually make?

We would like to invite you to a ‘Listen and Reflekt’ lunchtime seminar on Teams 1st June 2022. The subject for this seminar will be Learning from Incidents.https://reflekt.as/events/

Tuninter Flight 1153 was a Tuninter Airlines international flight from Bari International Airport in Bari, Italy, to Djerba-Zarzis Airport in Djerba, Tunisia. On 6 August 2005, the Tuninter ATR 72, a twin engine turboprop, ditched into the Mediterranean Sea. Sixteen of the 39 people on board died.

About midway through the flight at 7000 meters, the right engine stopped. After a further 3 minutes the left engine also stopped. The crew followed the relevant check lists to restart the engines including confirming that there was sufficient fuel on board. The nearest airport was Palermo on the island of Sicily and the captain declared an emergency and requested a landing. Unfortunately, there was not enough height to make a landing and the aircraft was forced to ditch in the sea about 43 kilometres from Palermo. The aircraft broke into three parts on impact.

The aircraft was type ATR 72-202. Following the previous days flight, the crew reported a fault on the fuel measurement unit. The flight mechanics replaced the unit in the cockpit. The crew on the day of the flight was the same crew that flew the aircraft on the previous day. The captain noted that the faulty fuel measurement unit was fixed, and that the measurement was higher than from the previous day. He then assumed that the aircraft had been refuelled. The crew confirmed that there was enough fuel inboard as part of the flight preparation checklists.

The flight mechanic that changed out the fuel measurement unit inadvertently installed a unit for the aircraft type ATR 42. The wings in the ATR 72 and ATR 42 are different and the there are different volumes for fuel storage. This meant that the ATR 42 unit gave an incorrect fuel reading. The above figure (left) shows the fuel level in the ATR72 using an ATR 42 unit. The figure (right) shows the fuel level in the ATR 72 using the correct ATR 72 unit. As you can see there is a discrepancy of about 500 kgs for each fuel tank, and this resulted in incorrect readings on the amount of fuel on board.

The fuel measurement units are almost identical, only the part number distinguishes them, 2250 for the ATR 42 unit and 2500 for the ATR 72 unit. More importantly the units are interchangeable and are therefore just waiting for a flight technician to install the wrong unit. This could easily have been avoided if the mechanical design prevented the wrong unit being installed. A simple design modification and the probability of the mistake is reduced to zero. Can you design your systems to reduce the probability of a mistake to zero?

Incidentally the crew were also at fault as they did not sign off a refuelling ticket since no refuelling took place. Had they followed this routine they may have discovered the faulty fuel measurement.