The ETTO Principle: Efficiency-Thoroughness Trade-Off by Erik Hollnagel

Author:Erik Hollnagel
Language: eng
Format: epub, pdf
Tags: A Cross-Cultural Perspective
Publisher: Ashgate
Published: 2009-04-22T04:00:00+00:00

A Reverse Fuel Situation

This case study concerns a company that operated a Douglas DC-3 for vintage charters and scenic flights. The DC-3 is a fixed-wing propeller driven aircraft, which first flew on 17 December 1935. Douglas built more than 10,000 planes of this type, which remained in use well into the 1970s, and is still flown for special purposes. The company discussed here had been doing scenic flights for a number of years and was licensed and approved by the Civil Aviation Administration. The technicians as well as the aircrew were also licensed and experienced.

The standard operation procedures state that the main fuel tanks always must be filled with the required fuel (reserve fuel included) for the flight and the auxiliary fuel tanks must have 45-minute reserve fuel. Due to the inaccuracy of the fuel gauges, the fuel tanks must be dipped before the flight to determine the correct fuel levels.

The flight for the day was a ferry flight from base to a nearby general aviation airport followed by a 1-hour scenic flight with 15 passengers, returning to the general aviation airport, and then a ferry flight back to base. On the previous day, the aircraft had returned from another flight where it had been refuelled totally and then used both the main and auxiliary fuel tanks. On shut-down the auxiliary tanks held the required fuel for the next day and the main tanks held approximately 1 hour’s reserve. On the day of the flight the aircraft was prepared and the fuel tanks dipped by the senior technician, but the information about the reverse fuel situation was not passed on.

During the briefing of the aircrew, the fuel requirement was confirmed by flight operations who knew about the reversed fuel situation but who failed to highlight the potential problem. During the pre-flight checks the captain directly asked a technician if the main fuel tanks had been dipped for the correct fuel requirement, and received an affirmative answer. On start up the main fuel tanks were selected since nobody at this stage had mentioned the reverse fuel situation.

Both the ferry flight and the scenic flight went off without any problems. Shortly after take-off for the return flight to base the left-hand engine began to run rough. The first officer was pilot flying and continued to do so as the captain took charge of the emergency. The left-hand auxiliary tank was selected as the right-hand engine began to run rough. While continuously selecting between auxiliary and main tanks left and right the captain could not restart either engine. The first officer carried out a successful forced landing and there were no injuries.

The ETTO principle can be used to understand how this situation came about. Even a quick look will show examples of ETTOing on all levels of the organisation.

• Negative reporting. The senior technician did not pass on the information of the reversed fuel situation as there was more than sufficient fuel on board for a safe flight. The pilots therefore worked on the assumption that the conditions were as normal.

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