very interisting article.although why would a newly built airplane after only flight tests would be scrapped,is a waste of time money labour and why not put the airplane on display in a museum for others to enjoy?

I have to agree with Carmine, great article, but what a tremendous waste of time, efford and money. And forget about a museum, they could have put that baby right in my back yard.

i am glad to know that you care about safety,and what the genaral public thinks.it may be very difficult and expensive to determine an air plane's flight worthiness,but sometimes we have to think outside the box.i am not sure how pressurization work in an air plane,or the process that has to be use.perharp the design and complexity of its mechanical and the sensitivity of the wireing make it difficult to perform other less expensive test.maybe the airplane companies need to consider designing their planes differently.

More info on the ultrasonic phased-array technique for NDE can be found at http://www.bercli.net/documentation/phased_array.htm (updated link).

With newer materials like carbon fiber and other composites, why can not aircraft manufacturers make use of them instead of the perennial aluminum that is less durable? Then they should also design the aircraft that sections can easily be replaced thus extending their flying lives longer. When I see aircraft bone yards split familiar aircrafts in only a few minutes for recycling a part of me is also dies with the plane especially if they have made historical flights in the past.

Boeings new airplane the 787 which has not flown yet
is made with composite materials and may not suffer from
the fatigue problems todays aircraft have.

Boeings new airplane the 787 which has not flown yet
is made with composite materials and may not suffer from
the fatigue problems todays aircraft have.

How frequent do the airliner conduct an inspection to an airplane?
Do they conduct it on daily,weekly,monthly or distance of flight basis?

I found this article very interesting.
This to me brings up another question. Why is it some airplanes last longer than others? Like, has anyone figured out why the DC3s can still fly while planes far younger are long gone?

I agree. A very interesting article.

Could anyone tell me how to get into aircraft recycling career?. As a Senior Project Manager with Aviation in my heart I would love to be managing projects to preserve aircraft.

Re. Louis, for one thing, DC-3s weren't pressurized airplanes, nor were B-17s or piston fighters. B-29s were pressurized but in a year or two's service I imagine they didn't go through nearly as many pressurization cycles as a jetliner.

In regards to fatigue cracks, it is interesting that the first DeHavilland Comet jetliners had rectangular windows - the window corners were the perfect place for cracks to propogate from, which caused the infamous catastrophic failures in early Comets.

Metals and their properties is a fascinating subject.

The answer to the question “why do some planes stay aloft longer than others?” is an easy one. Money money money! Is it worth it to keep em’ flying? Look at the balance sheet. Airlines and museums work on the same principle; they do what they can with the money they have. Of course, the military is a little different….

At first one would think with today's technologies, different materials could be used to increase the length of time planes remain in service. But after reading clay's comments, he hit the nail on the head, it's all about money...

-Stephen Personal Injury Lawyer NJ

How do airlines determine if metal fatigue has developed in their passenger-liners? Bob Eastin, an FAA specialist on aircraft fatigue, says, "[Airlines] are really relying on the manufacturer's maintenance programs. I think that it is great that they do rely on manufacturers. Why not? Mikhail at fat loss 4 idiots guide.

Yeah, the limiting TECHNICAL factor may be metal stress and fatigue, but the possible FINANCIAL limits are endless: engine fuel consumption vs upgrades vs scrappage, the structure of the original purchase [actual ownership vs lease], who owned the airframe and for how long, which airline had it last and for what purpose, etc. ad nauseum.

Most of the aircraft now in long-term storage in the desert will never fly again, though most of them are or could be made to be airworthy - just not economically.

These airplanes are technically not "worn out", but no one wants to spend the money to keep them flying commercially, because there are more economical alternatives. AA just announced a major conversion to 737-800s to replace a bunch of their MD-80s, not because the latter are so near to their technical demise, but because they use more fuel and are starting to become a maintenance nightmare. Same reasons you trade a used car for a new one....only in this case the used one never goes back on the road because no one wants it.

I have to agree with some of the other postings here. With today's technology and materials, one would think planes should last longer. If the lifespan of a plane can't be lengthen, there won't be enough museums around to showcase all the scrapped planes.

Scott
Philadelphia Wedding Photographer

In response to Louis Steiner's question about why DC-3's are still flying while many younger aircraft are not, I recall a conversion between the co-pilot of a DC-3 that a group of us was going to fly in and one of the passengers. He asked: "Is it safe to fly on an airplane this old?" to which the co-pilot responded:"How do think it GOT TO BE THIS OLD?!!"

Probably the main reason that the DC-3 is still in the air is because the aircraft is so underpowered that the airframe doesn't get a stressed as aircraft with more power. (I wonder if anyone ever though about replacing the Pratt & Whitney R-1830's with R-2800's during the war.) Also, the DC-3 is built like a tank with rivets to match. Flush-riveted, the DC-3 could probably fly 30 knots faster.

The DC3 is not underpowered. Like all designs it was built to fly at the speeds it works at. It can fly on 1 engine. I flew in a Super DC 3. It was a C 56(?)(Navy R-6D or some number). It was a Navy version and took me from Okinawa to Kyushu in 1953. It was a DC 3 with different wings and empennage, powered by R-2800s. Those engines drank gasoline and the airplane was more expensive to operate, but it flew faster. No commercial versions were sold that I know of. Ask Douglas about their swept wing Super DC-3.

During mountain travels in a motorhome, the stored water bottles fatigue from constant exposure to various altitudes and temperatures. They all eventually leak from the constant flexing. Same effect but more drastic for aircraft components. DaFlikkers

My brother is an aircraft mechanic who repairs smaller jets that fly domestic routes from Newark Liberty Airport. Due to the metal fatigue and the pressurization that the aircraft is put under, he tells me he is constantly changing fasteners and rivets on these aircraft. There is even a special technique to fasten the fasteners.

Can old airplanes be recycled into new ones? Why beverage cans or skateboards?

I understand why pressurization stresses the fuselage, but why does it stress the wings? The wings aren't pressurized, are they? EDITORS' REPLY: In a joint email we received from Deborah Hopkins of Lawrence Berkeley National Laboratory and Guillaume Neau of Bercli, LLC: "Although the wing isn't pressurized, pressurization of the fuselage might affect the stress state across the area where the fuselage
and wing are joined."

Aircraft maintenance has a lot to do with life span too.

For example the Joint STARS aircraft currently used as an intelligence gathering platform is based on old Boeing 707s, that have gone through a refurbishment to zero time them.

Fatigue strength is linear on semi-log paper, but must consider initial crack sizes (machine tool marks) crack growth rates.

Composites don't weaken by fatigue, but in compression, the stiffest part (the fibers) are pre-buckled, and so don't contribute, making them less efficient. In tension because of the complexity in putting them together and getting them to cure, the theoretical strength is significantly reduced. Then, the bearing strength of plastic composites is reduced again, so riveted or bolted composite structures take a double hit.

Some of the reason why an aircraft may be scrapped is economic: Their market niche has gone away. The BA-142 is an example of that.

You must also consider that the DC-3 remined in use because of operations cost, and the ability to perform duties that most airplanes cannot. The DC-3 even today is still a cheap medium size airplane to operate compared to a turboproped powered aircraft of similiar size like a king air for instance. In remote places like the bush of Alaska, or the Australian Outback the 3 can get into and out of rugged dirt strips carrying oversized cargo and it is big enough to be used as an air ambulance or a transport. In fact the army up in to the mid 70s used the DC-3 for a variety of purposes Such as transporting troops,hauling cargo, gunships, and as staff transports they were known as C-47s

Can anyone tell me how to get into aircraft recycling career?

In response to an earlier comment; the Super DC-3 was used by several smaller airlines. Capital Airlines was one of those. They sent three older DC-3's to Douglas who added a six foot section aft of the cockpit, installed the bigger engines and nacelles, modified the wings and vertical stabilizer and added steps to the cabin door to expedite passenger entry and exit to reduce loading and ground time. The conversion made a degree of sense on Capital's many stop flights, like The Tobacco Road routes from DC to Memphis with eleven stops, but was not a commercial success in competition with the Martin 202/404 and Convair's of the day.

How often are fuselage and wings (and any other stress areas) checked? Are these things that are checked on a flight-by-flight basis, or after a number of air miles? Whenever I've had a window view of a wing, I've often looked at the rivets and wondered how secure they must be. Have there ever been cases where rivets have come lose during a flight?

Re: Louis Steiner "...why the DC3s can still fly while planes far younger are long gone?"

The Douglas DC3 was designed in an era long before computerized finite element analysis (FEA), and designers weren't able to shave every ounce of weight from the airframes using manual design techniques. Planes of that era were often severely overdesigned for safety. This translates into long airframe life. Also, the DC3 is an unpressurized fuselage design, so it doesn't undergo the repeated skin stresses that modern airliners do.

Re: Briany Drake "Have there ever been cases where rivets have come lose during a flight?"

Not exactly, but on April 12, 1998 Aloha Airlines Flight 243, a Boeing 737-297 island-hopper, lost a large section of the fuselage roof, just aft of the cockpit. One flight attendant was blown out during the accident, but the pilot managed to land the plane safely. The plane was 19 years old and had undergone 89,090 pressurization cycles. Read about it in Wikipedia, "Aloha Airlines Flight 243".

Nondestructive evaluation (NDE) inspections are used both during production (to ensure that components start out free of defects) and during an aircraft's service life to detect cracks as small as 0.04 inch. Inspectors might, for example, take a close look at fastener holes located at the wing and spar junction. I hope that more and more inspections will be there so we will feel safe.

Under cyclic stressing, all Aluminum will eventually crack. Pressurization is necessary to fly comfortably at high altitudes without wearing an Oxygen mask. Pressurization cycles are easy to count. If I recall correctly, the Aloha failure occurred on one of the highest cycle 737's ever flown.

Wings are cyclically stressed by heavy turbulence, and high-g maneuvers. As for wing failures, the tragic wing failures encountered by two fire fighting airplanes a few years ago illustrate that failure mode. Flying low over mountainous terrain the plane experiences severe turbulence at max gross weight, resulting in very high stresses in the wing. Since the water-bombers often fly with higher fuselage weights than originally intended (water-bombers rarely carry anywhere near their internal wing fuel tank's design capacity so they can carry more water in the belly tanks), and as a result the stresses between the wing and fuselage are higher than originally designed (in turbulence, the weight of fuel inside the wing does not add to the stresses at the wing to fuselage interface.)

The resulting higher than anticipated stress levels increase the likelihood of cracks forming, and can also lead to much faster crack growth, which can quickly become catastrophic.

Airplanes are designed so that cracks grow slowly AND the cracks will be readily detected by inspection before they reach a "critical" length. Airplane inspection intervals are specified, in part, on the projected (and measured by testing), crack growth rates. These inspection intervals are typically thousands of flight hours. Occasionally a problem will be detected on an aircraft type that will require more frequent inspections to an area that has not proven to be as strong as intended. As planes get older, these inspections, which can be expensive to conduct (e.g. removing the aircraft's interior), may become increasingly frequent, and contribute to the aircraft's uneconomical operations, leading to scrapping.

Two things are working against the DC-3. First, DC-3s require periodic inspections of their wing attach areas, the "10,000 Hour Wing Pull", which is an expensive undertaking in itself. Many times an operator has paid to have the inspection performed, only to find the wing attach structure cracked, and the airplane unairworthy. Replacing cracked wing attach structure is far more expensive that the inspection. There have been several operators known to part out or scrap DC-3s when they reached the 10,000 hr wing pull interval. It is often cheaper to buy another DC-3 rather than to perform the inspection let alone any repairs that may be necessary.
Second is the phaseout of leaded Aviation Fuel. 100LL Avgas is supposed to be phased out this year. DC-3s can operate on auto fuel under an STC but their performance is hindered and their useful load is pretty seriously compromised from what I understand.
Sadly, I believe, these two factors will finally ground the astounding DC-3.

I often see at our local airport aircraft performing "touch and goes" Sometimes one aircraft will be doing this all morning. There would be no pressurization as the aircraft never climbs above a couple of thousand feet. Would these flying hours & landings count? EDITORS' REPLY: Other forms of wear and tear would be taking place.

Yes, fatigue cycles are important to limiting the life of an aircraft, but, I suspect, economics is a bigger factor for airline service. Is the equipment efficient to fly in terms of fuel consumption for revenue miles, costs for maintenence, crew requirements, is the latest avionics available for efficient useage? I'll bet these and corporate factors contribute more to retirements than pressurization cycles.

Heck yea, they can park one of them old f-4's,F-15 or F-14's out at Davis-Monthan in my front yard anytime.

I am not an aircraft mechanic, pilot, engine mechanic or related to flying in any other manner. At the same time I do fly commercial and occasional private as a passenger. I am pleased that all aircraft receive periodic inspections to make them safe. When I was in the U.S. Air force back in the 1950's, I used to fly occasionally in the C-119 cargo plane. We had to wear a parachute every time when taking off and landing, or in rough air. I never had to wear a parachute when flying commercial. There was more assurance that the wings would stay attached to the cabin on the commercial aircraft.

The early C-130 aircraft propeller blade tips exceeded the speed of sound and the area adjacent to the inboard engine's blade tips would cause the aluminum paneling to fatigue. The problem required this area to be replaced every now and then. The eventual solution was to change the gearing in the engines and re-pitch the prop so it could turn slower and still produce the same thrust. At least that was how it was explained to me. Sometimes there are solutions to longer life and sometimes there isn't. I always enjoyed flying in the C-130 in support missions.

Can anyone know what type of fuel cells or tanks are
used on the DC-10 and the L1011 older aircraft, compared
to the newer aircraft of today such as B767 & A320 etc:

Thank you!

All larger modern transport aircraft utilise an intergrated tank design; the tank is part of the wing and aircraft structure, and is sealed internally during construction. The most common configuration is one or two tanks in each wing, and one large tank in the center section between the wings. Certain long-range models, like the Airbus A340-LR will have auxiliary tanks in otherwise unused empty spaces like the vertical stabilizer.

In response to Russ's very interesting comment that the crew always had to wear a parachute in a C-119, Flying Boxcar. My first jump to qualify for airborne status was a C-119 in 1964 and whenever I was in C-119 I always wore a parachute as a paratrooper.

I am an aicraft maintenence engineer and have worked on both old (B707, B727,F1-11) and new (A330/340) aircraft and the design differences are very obvious. Modern materials and production techniques and intended usage are the factors involved in how a manufacturer builds an aircraft. When an aircraft recieves a "heavy check" it is a costly endeavor in terms of labour and parts/materials. (when an aircraft isnt flying generating revenue it is a liability).
During most heavy checks the cabin is completely stripped out to have inspection work done. A lot of attention is paid to high stress areas eg window and door openings and corrsion prone areas such as the suppporting structure of galleys and lavatories. An older aircraft will always have corrosion in some part or other and controlling this is a big task. Some of the 707s I have seen are still airworthy today but the older engines (PW JT3d) are just way too costly to run, hence the USAF re-engining most of the KC-135 fleet with GE CF6 engines.Some of those old girls would have in excvess of 100,000 pressurisation cycles on them. It is an operating cost vs replacement cost decision.

There is a lot of good info mentioned above and it's greatly appreciated. However, what comes into my mind before I get on any plane is "I hope everyone from the maint crew to pilots has done their job today and didn't take any short cuts". From a quality control stand point, who oversees the actual testing while it's being conducted and is this person an outside agent and qualified? Or better yet, is there any part of a commercial plane that receives a daily Preventive Maintenance Check (PMC) for servicability?

Technology is so advanced today that if a spaceship can be blasted off into space so to can a plane be built to last indefinately.
Plane can be designed to last in all weathers including tropical storms, lighting and thunder.
All the parts which are not being used for aviation once the lifespan is over can be recycled.

To add to the above post the Airbus is limited to 20,000 cycles and then it becomes beer cans.

All metals, except steel, will fatigue if exposed to cyclic loading. Steel will not if loaded under a certain threshold, but it is too heavy to make aircraft from. Composites have many benefits, but they also have their modes of failure. Equally sophisticated methods are used to inspect composites for delamination, deterioration due to enviromental or stress as are used to inspect for fatigue cracks on metal aircraft.

This is true that jetliners are scrapped and Classic planes are still capable of taking flights , it all depend on pressure cycles and what i think is that jetliners face more pressure cycles than classic planes due to their speed and volume and many more aspects.

http://www.pakcolours.com/blog/why-classic-planes-are-flying-and-jetliners-scraped/

Hi
I am interested in the Engineering aspects of airplanes.
(Underneath the planes skin is of most interest to me (spars, ribs, stringers, types of landing gear but particularly the methods of joining etc).

How do airplane manufacturers physically join aircaft sections together ?
1)Nose section to fuselage etc, 2) wings to fuselage 3) plugs in fuselage

I have searched the internet but have not found anything useful

Photographs during construction would be very helpful.
It would be great if they were available somewhere. Would there be sites where any resources would be avaliable for download ?
Would you be able to point me in the right direction?

Thankyou and regards
Geoff Brown
Henty NSW
Australia. EDITORS' REPLY: Great questions. The answers vary with each aircraft design however, so generalizations can't be made that will apply to all airplanes. If you list some of the aircraft you're most interested in, perhaps some of your fellow readers will have suggestions for you.

How much thrust and lift/wing area would it take to get a 4.5million pound airplane off the ground.I know there isnt one but just for wanting to know.Say it was a triangle shaped lifting body with six engines with afterburners and hydrogen injection in the hot exaust for increase in power say the size of a 747-300. Would a 6 mile runway help it to get up to fast speed and is it possible to lift 4.5 million pounds off the runway with any size wing area? if you had 800,000 lb thrust from six modified turbofans and a super long runway would it eventually climb maybe with help from jato bottles or solid boosters? love your site
tim
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As some readers have eluded to in their previous posts, economic life is becoming more of an issue than fatigue limits.

The rise in the price of oil and the incredibly competitive nature of the airline industry has meant the early retirement of some airframes.

For example, my employer recently disposed of some Airbus A340-300's which were not an ideal fit for our route structure. Who was the highest bidder? A scrap yard!

This seems incredible when just across the ramp, 50 year-old DC-8 freighters are still working hard while a 20 year old modern airliner is sent to the grave. Part of the reason, interestingly enough, is that the A340 shares many common parts with the A330. The parts are worth much more to an A330 operator than put together as an airworthy airframe and the 4-engine economics are not attractive!

On the other hand, DC-8 parts are not worth much to anybody other than the few worldwide DC-8 operators, so at this time the aircraft earns its keep for cargo companies.

The question I am interested in is, how often is an aircraft serviced. EDITORS' REPLY: It depends on the aircraft type and how it is used, among other factors.

Very interesting article and follow-up comments! I'm a "retired" airline A&P mechanic (technician, engineer, whatever term you want) with about 22 1/2 years time with an airline that used to have a bunch of hangars in MSP.
Had about 3 years in their sheetmetal department working heavy checks and overhauls (another 3 years or so prior to that, doing similar work for a colorful airline that used to have its maintenance base at Love Field). That background prepared me well, to be able to handle the pretty common occurances of what you may call "Ramp Rash", when I took a position working Line Maintenance. The Tarmac gets pretty busy and sometimes crowded with equipment. Even with everybody trying to be cautious, accidents happen. Aircraft parked at the gate routinely get hit by baggage tugs/carts, belt loaders, main deck loaders, lav trucks, galley service trucks, air conditioning and heating carts, Jetways, stairs, etc.

Normally, the damage can be inspected and evaluated, the damage removed and a repair installed (all by stringent Structural Repair Manual procedures published by the aircraft manufacturer) and the aircraft can be sceduled on a revenue flight the next morning. Other times, more severe damage would ground the ship longer or, in rare instances, an unpressurized ferry flight back to the main base would be needed (with a special FAA permit, and no passengers allowed on board.)

So, my concerns are with this next generation of aircraft that are incorporating more extensive useage of composite materials in their fuselage construction. Sure, it allows for less weight/less fuel consumption benefit, but the implementation of field repairs to ramp damage is what interests me. I think this area might make for another great article in a future issue!

The article is a good insight about the safety of an aircraft. I am an ardent watcher of aircraft crash investigations, don't know why but it's an inborn quest to know all about the life and safety of an aircraft.

Anyone know of any noise tests performed on the R-3350 aircraft engine used on the B-29 and the C-119 aircraft??

Can somebody explain why a normal airline plane will be diverted of course 45 degrees for hundreds of miles then diverted back to resume its normal flight path.
This happens in Australia regularly and not in the same area.
Ihave noticed this on ''Flightradar''