MEDA in Practice
This case study illustrates how the MEDA process can help operators identify factors in the work environment that can lead to serious events.
An operator's 767 was diverted when the pilot reported problems with the fuel flow indication system. After a delay, all 210 passengers were flown out on another airplane, which had been scheduled for an overnight check at that airport.
Extensive troubleshooting revealed debris in the fuel tank, including tape, gloves, and several rags that had clogged some of the fuel lines. The debris had been left during fuel tank leak checks and repairs and had not been found by the inspector at the end of the check.
Scott and Dennis were the two maintenance technicians who performed the fuel tank leak checks and repairs. The MEDA investigation showed that Scott started the series of tasks during the third shift. He used the Airplane Maintenance Manual (AMM) as a reference to do the fuel tank purging and entry procedure. Then, he started the area-by-area leak checks and repairs as shown by the operator's work cards. Scott had trouble moving around in the tank because of his above-average height and weight. Scott made minor repairs in some areas of the tank, but his shift ended before he finished the task. Wanting to get out of the tank as soon as possible, Scott left the tape, gloves, and rags in the tank for Dennis to use to finish the task on the next shift.
Scott checked off the tasks he had completed on the signoff sheets in front of each work card. He also wrote in the crew shift handover report which tank areas had been checked and repaired and in which area he had last worked. However, he did not write in the shift handover report that he had not finished checking and repairing the complete tank, and he did not write down that he had left equipment in the tank. There was no overlap between shifts, so Scott left before the mechanics arrived for the next shift.
James was the lead technician on the next shift. He read the shift handover report. He did not notice that Scott's work card was not signed off, so he assumed that Scott's tank was finished and assigned the rest of the leak check and repair work cards for the other fuel tanks to Dennis. Dennis was the smallest member of his crew and found it easy to work in the fuel tanks.
Dennis completed the leak checks and repairs on the tanks that Scott had not worked on. Dennis saw that the AMM had recently been revised. Technicians were now supposed to count all the gloves, rags, and other equipment that were taken into and out of the fuel tanks to make sure that all equipment was accounted for. He also noticed that the work cards had not been updated to reflect these changes to the AMM. Dennis followed the instructions because they were probably added for safety reasons. Consistent with the AMM revision, he remembered hearing that his employer had moved to a process that called for each mechanic to take all equipment out with him when leaving a tank, even if the task was not completed. He noted to himself that the new process had not yet been briefed at a crew meeting. Dennis finished the remaining fuel tanks shortly before the airplane was due for final inspection. He signed off the remaining work cards and handed them over to his lead, James.
James (following a standard procedure at that operator) put all of the fuel tank work cards together in one stack. Then he attached one inspection signoff sheet to the outside of the stack. James handed this and other stacks of work cards to Bill. Bill, the maintenance inspector, did the final inspection.
The fuel tank access panels were still open when Bill did his inspection. He used a company-provided flashlight and mirror to inspect as much of each fuel tank as he could through the access panel without going inside the tanks. This was an acceptable level of inspection at this particular operator. However, Bill could not see the entire area inside of each fuel tank from the access panel openings. Bill stated during his MEDA interview that the design of the fuel tanks made it impossible for him to see every area using the flashlight and mirror. He also said that the colors of the gloves, tape, and rags were almost the same color as inside the fuel tanks. Bill signed the inspection sheet for each of the fuel tanks. The fuel tank access panels were then closed.
The MEDA investigation also found that the AMM procedures for the fuel tank purging and entry, fuel tank leak checks, and fuel tank repairs all contained instructions to make sure all objects were removed from the tanks when the procedures were complete.
This investigation enabled the operator to develop a number of recommendations to prevent a similar event from occurring in the future. These recommendations include:
- Changing work cards to include the reference, "Equipment removed from tank."
- Using brightly colored rags, gloves, and tape that contrast with the tank color.
- Changing the inspection process to a full-entry inspection or using better lighting to perform the inspection.
- Providing all of the mechanics with information and training on the new tools and equipment removal process.
- Delegating fuel tank work to smaller mechanics.