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Episode 59 Aircraft Metal Fatigue
Aviation Metal Fatigue is a concept for you to understand aircraft maintainance in a way.
Nick: Hello, everyone. Thank you for tuningin to 5 minutes with AOPA-China.
Claire: Let’s start with a piece ofaviation news.
Nick: A 22-year-old Chinese cadet with hisinstructor at US aviation academy died in a plane crash.
Claire: Condolences to them and theirfamily. It’s such a great loss.
Nick: The US NTSB is leading theinvestigation now. It’s yet unclear who was flying the aircraft and what causedit to go down.
Claire: The crashed plane is a twin-enginePiper PA-34 which was manufactured in 1973.
Nick:So it is already 46 years old. Is ittoo old for a trainer?
Claire: Actually it’s normal for an oldplane to continue flying if it is well maintained. But if it is not, it doesneed retire. Anyway we are not jumping into any conclusions here, we will waitfor the official investigation report for this accident. Today, we want tocover the topic of what can lead a plane to retire.
Nick:You may be aware that there are manyold airplanes still flying in today's sky. As a matter of fact, An aircraft'slifespan is measured not in years but in pressurization cycles. Pressurizationcycle refers to the amount of time that the aircraft is kept under pressurefrom flight. Each time an aircraft is pressurized during flight, its fuselageand wings are stressed. Both are made of large, plate-like parts connected withfasteners and rivets, and over time, cracks develop around the fastener holes.Engineers call it metal fatigue.
Claire: Yes, if you’ve ever taken a paperclip and bent it back and forth until it breaks, you know at least a littlesomething about metal fatigue. It’s the cyclical application of pressure on themetal of the paper clip that eventually causes it to snap. The same can happenwith aircraft.
Nick:Each pressurization cycle involvestakeoff and landing. The fuselage is most susceptible to fatigue, especially onshort hauls where an aircraft goes through pressurization cycles every day. Onthe other hand, aircraft used on longer flights experience fewer pressurizationcycles, and can serve for more years.
Claire: How to determine the metal fatiguelevel that can cause dangerous damage to an aircraft?
Nick: There is a parameter called Limit ofValidity, or LOV. It sets the standard for metal fatigue test evidence.Basically, LOV is a measure of time a particular aircraft has before widespreadmetal fatigue becomes an issue. The manufacturers and operators of aircrafthave this information. Airlines are really relying on the manufacturer'smaintenance programs. The manufacturers design the aircraft to be trouble-freefor a certain period of time. There are maintenance actions to preclude anycatastrophic failures, but that's not to say the aircraft might not experiencemetal fatigue before those times. When you get to a certain point in theaircraft's lifespan, you need to inspect or replace certain parts.
Claire: Moreover, manufacturers must alsoadhere to several airworthiness directives set by authorities, for example, FAAin America. The AD focus mainly on identifying areas which are mostlysusceptible to widespread metal fatigue. They require manufacturers to makecostly inspections and repairs before the thresholds for airworthiness arereached.
Nick: Last week, we saw a variety ofwarbirds and vintage aircraft flying in Airventure Oshkosh. The models areantique and classic, but the airplanes look new. Don’t they suffer metalfatigue?
Claire；I think someaircraft are maintained in good condition. They are not pressurized asjetliners. Therefore, they suffer less metal fatigue, lasting for more years.And some are restored aircraft. Restoring involves disassembly of a knownquantity, inspecting and cleaning the component parts, repairing or replacingthe necessary parts, and then reassembling the airplane. Above all, therestored airplane should comply with AD too.
Nick：Now I see howimportant a role that maintenance staff play in aviation. That brings us to theend of episode 59. Any comments or complaints are welcome to tell us. Find uson WeChat, Facebook, Twitter, Ximalaya and any podcast platform. If you like usand want to support us, just tell your favorite episode to your friend. See younext week.
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By 上官琪琳 李方旺Aviation Metal Fatigue is a concept for you to understand aircraft maintainance in a way.
Nick: Hello, everyone. Thank you for tuningin to 5 minutes with AOPA-China.
Claire: Let’s start with a piece ofaviation news.
Nick: A 22-year-old Chinese cadet with hisinstructor at US aviation academy died in a plane crash.
Claire: Condolences to them and theirfamily. It’s such a great loss.
Nick: The US NTSB is leading theinvestigation now. It’s yet unclear who was flying the aircraft and what causedit to go down.
Claire: The crashed plane is a twin-enginePiper PA-34 which was manufactured in 1973.
Nick:So it is already 46 years old. Is ittoo old for a trainer?
Claire: Actually it’s normal for an oldplane to continue flying if it is well maintained. But if it is not, it doesneed retire. Anyway we are not jumping into any conclusions here, we will waitfor the official investigation report for this accident. Today, we want tocover the topic of what can lead a plane to retire.
Nick:You may be aware that there are manyold airplanes still flying in today's sky. As a matter of fact, An aircraft'slifespan is measured not in years but in pressurization cycles. Pressurizationcycle refers to the amount of time that the aircraft is kept under pressurefrom flight. Each time an aircraft is pressurized during flight, its fuselageand wings are stressed. Both are made of large, plate-like parts connected withfasteners and rivets, and over time, cracks develop around the fastener holes.Engineers call it metal fatigue.
Claire: Yes, if you’ve ever taken a paperclip and bent it back and forth until it breaks, you know at least a littlesomething about metal fatigue. It’s the cyclical application of pressure on themetal of the paper clip that eventually causes it to snap. The same can happenwith aircraft.
Nick:Each pressurization cycle involvestakeoff and landing. The fuselage is most susceptible to fatigue, especially onshort hauls where an aircraft goes through pressurization cycles every day. Onthe other hand, aircraft used on longer flights experience fewer pressurizationcycles, and can serve for more years.
Claire: How to determine the metal fatiguelevel that can cause dangerous damage to an aircraft?
Nick: There is a parameter called Limit ofValidity, or LOV. It sets the standard for metal fatigue test evidence.Basically, LOV is a measure of time a particular aircraft has before widespreadmetal fatigue becomes an issue. The manufacturers and operators of aircrafthave this information. Airlines are really relying on the manufacturer'smaintenance programs. The manufacturers design the aircraft to be trouble-freefor a certain period of time. There are maintenance actions to preclude anycatastrophic failures, but that's not to say the aircraft might not experiencemetal fatigue before those times. When you get to a certain point in theaircraft's lifespan, you need to inspect or replace certain parts.
Claire: Moreover, manufacturers must alsoadhere to several airworthiness directives set by authorities, for example, FAAin America. The AD focus mainly on identifying areas which are mostlysusceptible to widespread metal fatigue. They require manufacturers to makecostly inspections and repairs before the thresholds for airworthiness arereached.
Nick: Last week, we saw a variety ofwarbirds and vintage aircraft flying in Airventure Oshkosh. The models areantique and classic, but the airplanes look new. Don’t they suffer metalfatigue?
Claire；I think someaircraft are maintained in good condition. They are not pressurized asjetliners. Therefore, they suffer less metal fatigue, lasting for more years.And some are restored aircraft. Restoring involves disassembly of a knownquantity, inspecting and cleaning the component parts, repairing or replacingthe necessary parts, and then reassembling the airplane. Above all, therestored airplane should comply with AD too.
Nick：Now I see howimportant a role that maintenance staff play in aviation. That brings us to theend of episode 59. Any comments or complaints are welcome to tell us. Find uson WeChat, Facebook, Twitter, Ximalaya and any podcast platform. If you like usand want to support us, just tell your favorite episode to your friend. See younext week.