What is Damage Tolerant Design?
Damage Tolerant Design (DTD) is a way of designing an aircraft in such a way that it will last a long period of time, corrosion resistance, be able to sustain defects and be able to safely be repaired, while also able to withstand the fatigue on the aircraft in the air.
History behind Damage Tolerant Design:
DTD is a critical part of designing aircraft, as it can provide a safer, lighter and more efficient machine. In this section, I will look at various examples of how an aircraft were affected by defects in their design, and how it affected the aviation industry as a whole.
Aloha Airlines Flight 243
It was later discovered that his aircraft suffered a sudden, and explosive decompression resulting in a large section of the roof being torn off taking a flight attendant. The aircraft then landed quickly, suffering one fatality and 65 injuries. The aircraft was determined to be damaged beyond repair, and was written off. This incident had far reaching effects on the aviation industry.
It was determined by the US National Transportation Safety Board that the cause of the incident was caused by metal fatigue by crevice corrosion, made worse by the exposure to the salt and humidity around Hawaii.
The maintenance programme for the aircraft was determined not sufficient, had a failure to adhere to an FAA Airworthiness Directive 87-21-08 set out by Boeing.
de Havilland Comet
This aircraft had multiple incidents, stemming mainly from hull issues (square windows), and loss of control by the pilots. Resulting from such a poor flight history, its Certificate of Airworthiness for early versions were revoked, and the aircraft was pulled from production. Modern aviation learned from the comets mistakes, by suffering catastrophic depressurisation caused in large part by cracks induced by the square windows buckling to the pressurisation from within the aircraft.
Explanation of the development of Damage Tolerant Design
Modern aircraft manufacturers have learned from previous generations of airplanes and their faults. At the beginning, the early jet aircraft such as the de Havilland Comet paved the way for the jet age. It did however, indirectly inform other aircraft manufacturers of the differences between jets and the conventional (at the time) piston driven aircraft. These differences included square windows, thin wings and a general unfamiliarity with the aircraft among flight crew and pilots. This led to many pilot error related crashes in the early days of the Comet. Learning from this, modern aircraft are designed with rounded windows, to better distribute the pressurisation load along the fuselage skin. The crash of Aloha Flight 243, served as a reminder to the industry to pay attention to Bulletins from aircraft manufacturers, but it also was a reminder to always keep strict maintenance practices (i.e servicing every two years) and regular maintenance as well.
Explanation of the technology of Damage Tolerant Design:
Carbon fiber has become used more extensively in airframes over time, after it has gotten popular usage in planes such as the Airbus A350 and the Boeing 787 Dreamliner. The advantages of Carbon fiber is that it is extremely strong and rigid, such as being used in the wing tips of the Airbus A350. It can take momentous load, while still being light enough to be able to lift.
3D Printing Manufacturing:
In recent years, a new technology called 3D Printing is being used by the likes of Boeing to print a 777x wing trim tool. By 3D Printing it, the aircraft saves in weight, and time manufacturing time. The piece usually takes 3 months to manufacture, compared to the 30hrs with the 3D Printer. Airbus and Rolls Royce have also began using 3D Printing in the A350 – 1000s XWB-97 engine. While the technology is new, it is promising as a fast way of manufacturing parts for aircraft while being light at the same time.