How Operators Keep Track of Aircraft Defects

Like any machine, aircraft will inevitably encounter problems and require repairs. This can be complicated, as aircraft are highly intricate structures consisting of hundreds of systems. The more systems there are, the more there is that can go wrong. Repairs can take hours, days, or even weeks. Getting an aircraft back in flight quickly is a top priority, but more important is getting the aircraft back in flight safely. As such, aircraft are not only designed to be able to fly with a single defect, but with many. This blog will explain how operators keep track of faults as well as how to know which aircraft are safe and which are not.

Generally speaking, each aircraft must legally have an aircraft maintenance log (AML). This is traditionally a large paper book used to record the details of every flight, every technical fault that occurs, and any work done by engineers to rectify said faults. After every flight, the captain fills in the details of the flight, such as the fuel loaded and the flight times. This allows engineers to monitor how many hours and flight cycles the aircraft engines have flown. Furthermore, the captain must denote any defects with the aircraft that may have occurred during a flight, including those occurring in the cabin.

On modern aircraft, such as the Boeing 787 Dreamliner, a more advanced type of maintenance log has become popular: the electronic logbook (ELB). Rather than relying on the manual entry of information, the ELB, using the aircraft communication system, feeds real-time information about the technical status of the aircraft to various departments within the airline’s operational infrastructure.

When an aircraft defect is detected, the captain must ensure it is properly recorded. When using a paper logbook, what is logged is simply the interpretation of the captain and crew. This can be a problem because, when there is no reference to an exact defect code, the engineers have a more difficult time assessing what the actual problem is. When using an ELB, the system automatically correlates entries and offers standardized definitions for problems. This makes the problems far less ambiguous and allows engineers to clearly understand what is wrong and how it can be fixed. Traditionally, problems that do not directly affect the safety of the aircraft in flight, such as defects with seats or other issues in the cabin, are recorded in their own log.

In a perfect world, all defects would be addressed and rectified prior to each flight. However, this is just not realistic. Instead, aircraft are designed such that almost all systems have a back-up, with some even having back-ups for the back-up. This enables aircraft to safely fly even while some systems are not working properly. But how do operators know which defects are tolerable and which are not? This is where the dispatch deviation guide (DDG) comes into play. The DDG is a list of every single defect that could potentially occur on an aircraft. Within it, there are two sections: the minimum equipment list (MEL) and the configuration defect list (CDL). The MEL is used to denote inoperative aircraft systems while the CDL denotes parts that are missing from the aircraft.

When a defect is listed in the DDG, it is done so with a letter grade depending on the importance of the part and the time frame in which it must be repaired. Category A items must be fixed immediately, category B within three days, category C within ten days, and category D within 120 days. The category will determine the severity of the problem as well as whether or not the aircraft is able to fly.

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September 27, 2022

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