War weary airplanes, who decided and on what criteria

[FLYBOYJ]

It would not be army if there were not rules and lots of forms i think. And i think it is strange we cant find the "rules"

Oh they're out there!!!! You'll have to look in the old AAF regs and TOs. Many of the outdated regs pertaining to aircraft maintenance are hard to find (at least in my experience).

 

[FLYBOYJ]

I presume aircraft are like most things in engineering. A structure can be repaired if it is damaged following procedures but those procedures apply to a structure not previously repaired and a separation is required between repaired areas,a point is reached where it is easier and safer to replace the whole thing. Aircraft made on an assembly line are not so easy to work on, I would imagine getting a burned out/shot up fuselage back to A1 condition would be a nightmare for the electrics and hydraulics.

You're correct to a point. As far as "assembly line aircraft" not being easy to work on, it depends on the aircraft. Part of the design team on some aircraft involve maintainability engineers.

 

[FLYBOYJ]

thinking about this...they must have abandoned this idea or at a certain number of hours do major overhauls because the B52s have been flying for a LONG time. maybe flyboyj has the answer for that one

In this case, the USAF has worked long and hard with Boeing to extend the B-52 life. As I have mentioned many times, this is done at Tinker AFB

 

[Shortround6]

thinking about this...they must have abandoned this idea or at a certain number of hours do major overhauls because the B52s have been flying for a LONG time. maybe flyboyj has the answer for that one

I read somewhere that some B-52s had the wing to fuselage joints replaced 4 times and that was over 15 years ago
What the AIr Force will spend to repair old air frames in peace time when congress is NOT buying new planes is a lot different than what would be spent on repairing planes in war time with a steady stream of new aircraft arriving in theater.
You not only had flak damage you had "taxi" damage and not all landings were smooth ones. After a certain number of hard landings (and not hard landings are equally hard) an air frame could take on a bit of tilt to one side or the other

Just taxiing a heavily loaded (over loaded) aircraft on sod fields might strain things.

 

[nuuumannn]

Modern aircraft are designed with maintenance criteria set by the manufacturer and a maintenance schedule is laid down for each type based on the manufacturer's recommendations, although operators can and do make suggestions based on operating experience. After the war there was a thing set up called the Maintenance Steering Group, who made calls regarding repeat maintenance of critical rotable items during scheduled maintenance. Operators found that during maintenance, parts were being replaced that didn't need to be under the manufacturer's recommendations, so the MSG went back to the manufacturers of each component and the aircraft manufacturers and suggested longer time between overhaul of specific rotable components. The B747 benefitted from this all and the main benefit to maintenance firms is cost; if a part doesn't need fixing, don't touch it.

A bit off topic, but I presume wartime aircraft had similar TBO requirements, but under the stresses of wartime operations these might slip, particularly if operating on forward bases away from the supply chains. I'm not too sure about requirements during wartime, but many things would be taken into account. If, for example your unit is running short of aircraft and supply of new components is limited, you'd do what you can to keep the thing flying with whatever repair was deemed necessary. These days the rules are far more stringent, of course, but even in wartime, keeping the maintenance schedule would have meant longer life out of your airframes and engines. If your unit was near supply chains, then the easier it was to stick to maintenance schedules as laid down by the manufacturer and if aircraft or components are too badly damaged, then replacement might not be an issue.

In peacetime the logistic supply chain means that any major repair can be carried out in accordance with the manuals, really, but during the war, that wasn't always the case.

 

[soulezoo]

And sometimes time and maintenance limits are exceeded unsafely.

Example: C-141's were originally spec'd for 27k hours of airframe time. The conversion to "B" models increased fuselage length and overall capacity (and weight). TCTO's were issued as the aircraft aged for "wingbox" modifications and special inspections as the box started to crack in certain places and any number of aircraft started to have weight restrictions placed on them.... but still they flew.

I was a flying crew chief on one old 141 (over 44k airframe hours) during the Bosnia/Kosovo conflict. This aircraft had a defective wing box with the weight restriction in place. We had just flown cross country (USA from west to east) and upon landing I start my walk around. as I come around the nose from port to starboard I start to smell jet fuel. I see a huge puddle on the ground and start to look up. At the forward wing root from under the "sail panels" is a stream of fuel coming down the side of the fuselage 3 feet wide. And I mean streaming down... From the rear wing root was another stream about 18 inches wide and another puddle of fuel collecting there.

Long story short... I could not find the source of the leak. A 5 man fuel cell crew was dispatched from McGuire AFB and they worked all night long with sheet metal crew at the base I was at tearing that bird apart to find the leak. They found nothing and buttoned up the plane and signed off the forms with "no discrepancy found".

I flew to Europe and back with another 50 or 60 hours of flight time on that mission without another sign of a leak. And no one could ever offer a satisfactory explanation. It was at that point I knew I was done flying 141's. That particular tail number was retired shortly thereafter.

So to the point of the OP, it tends to be a complex decision with greater amounts of politics and need in play over safety and engineering.

 

[soulezoo]

In peacetime the logistic supply chain means that any major repair can be carried out in accordance with the manuals, really, but during the war, that wasn't always the case.

This while according to common sense is true, it is not always the case. See my above post.

During the Clinton years, maintenance money was so strangled that we often couldn't get light bulbs for the plane. Often had to bring toilet paper from home for a mission. I could go on and on, but what happened in terms of widespread maintenance neglect was a travesty and often at the expense of safety... yet the mission went on. "Just make it work".

What was priceless was to see the faces on space A pax as I beat the hell out of the aircraft with a hammer to make it work. Sometimes in flight....

 

[chuter]

I'd guess the "War Weary" designation was strictly on condition, as opposed to predetermined cycles or hours. I've seen a number of aircraft with bunches of "working" (if they're working then what's wrong with 'em?) fasteners that might be impractical to replace if new aircraft were continually being supplied. So you remove a long line (or lines) of rivets on, say, a spar flange (is the aircraft shored?); are the holes needing oversized? Probably. Is there enough ED (EM for Boing - lol) for the larger fasteners? Do you have the larger fasteners? Has engineering approved wholesale replacement with larger fasteners in this area? The plane will still fly (hey! it flew yesterday!), it's not like oH, heck! the rivets are all of a sudden all loose! So, at some point someone decides the rivets in certain areas on a plane are getting a little too loose to trust to combat flying. ---> and/Or <--- There are difficult to repair cracks adding up or the repairs on those cracks don't inspire full confidence due to maintenance or engineering limitations ... you get the idea.

I don't think corrosion was seen as a huge issue back then (that's my biggest moneymaker - then cracks.)

 

[pbehn]

I don't think corrosion was seen as a huge issue back then (that's my biggest moneymaker - then cracks.)

The war only lasted five years during which there were over 20 marques of the spitfire, how many planes do you work on under 5 years old?
Someone posted a stat on the US air force, I cant remember the percentage but I think that today most US pilots are flying planes older than themselves.

 

[drgondog]

War Weary as labeled by AAF was a threshold based on airframe hours - different from 'unsafe to fly' based on other factors like major bending of an airframe with damage type such as severely deformed longerons in the fuselage. Many WW Mustangs for example, were pressed into operations when a maximum effort was required. WW was a judgment, not an objective flight safety criteria.

There were no sophisticated Zyglo or X-Ray Penetrant methods to detect stress cracks ordinarily hidden from sight unless major inspections are performed at scheduled hours. Basically most WW bombers had a far higher threshold than fighters because of the Design Limit differences and many WW B-17s and B-24s were older models replaced by better equipment and no longer required for operations.

That said WW wasn't applied to observable abnormalities such as skin buckling, popped rivets, etc - which were a sign of the airframe exceeding design limits pointing to near failure and destruction. These a/c were inspected by Engineering officer and most frequently Salvaged Class 26. Don Gentile's Mustang "Shangri La" was an example of the Salvaged Category.

 

[stona]

Modern aircraft are designed with maintenance criteria set by the manufacturer .

Servicing procedures were at least considered in the design of WW2 aircraft.
A&AEE criticisms of the Whirlwind (I appear to be bashing this aircraft, but it is just an example I have to hand) included perceived problems in this respect.
For example, Fred Rowarth, Chief Engineer at the A&AEE was unhappy that because the ducted exhausts were constructed with more than sixty nuts and bolts, regular examination of the exhaust manifolds would be impossible. To check the level of the hydraulic fluid required removal of the entire nose cone. It was impossible to reach the rearmost pairs of the Peregrine's spark plugs without removing the coolant header tank. There were more.
The fact that these criticisms were made shows that at least some consideration was given to the maintenance of aircraft, not just the Whirlwind, if and when they entered service.
Cheers
Steve

 

[yulzari]

The war only lasted five years during which there were over 20 marques of the spitfire, how many planes do you work on under 5 years old?

You know I could have sworn that my father served in WW2 during 1939 (France), 1940 (France, Egypt). 1941(Egypt, Iraq, Iran, Syria), 1942 (Egypt, Libya, Morocco, Algeria) 1943 (Tunisia, Italy), 1944 (Italy), 1945 (Italy) which I make 7 years.

 

[pbehn]

You know I could have sworn that my father served in WW2 during 1939 (France), 1940 (France, Egypt). 1941(Egypt, Iraq, Iran, Syria), 1942 (Egypt, Libya, Morocco, Algeria) 1943 (Tunisia, Italy), 1944 (Italy), 1945 (Italy) which I make 7 years.

I wasnt meaning to cause offense just discussing the European air war which kicked off for real in 1940 and ended in early 1945 when the LW were just about out of planes pilots and fuel.

My father joined up in 1942 but was not de mobbed until 1948, his three years peace time in the far east looking after released POWs affected him more than his 3 years active service in a destroyer engine room..

 

[drgondog]

Obviously depends on whether his TD started in Sept 39 and ended VE Day May 45. The math favors a minimum of 5 years and 9 months

 

[chuter]

The war only lasted five years during which there were over 20 marques of the spitfire, how many planes do you work on under 5 years old?
Someone posted a stat on the US air force, I cant remember the percentage but I think that today most US pilots are flying planes older than themselves.

Haha - that was a rather rhetorical statement on my part, just giving my personal experience for perspective. I work on newer (months old) planes about once a week, usually mods (scimitars on 737s). By contrast we've had an overnight 747-4 in for bilge cleanup after a fluid spill in the aft pit that's been hanging around for the last month and a half because of massive corrosion found there (two months out of its second Chinese overhaul) and it has only 14 months service left.

 

[chuter]

War Weary as labeled by AAF was a threshold based on airframe hours - different from 'unsafe to fly' based on other factors like major bending of an airframe with damage type such as severely deformed longerons in the fuselage. Many WW Mustangs for example, were pressed into operations when a maximum effort was required. WW was a judgment, not an objective flight safety criteria.

There were no sophisticated Zyglo or X-Ray Penetrant methods to detect stress cracks ordinarily hidden from sight unless major inspections are performed at scheduled hours. Basically most WW bombers had a far higher threshold than fighters because of the Design Limit differences and many WW B-17s and B-24s were older models replaced by better equipment and no longer required for operations.

That said WW wasn't applied to observable abnormalities such as skin buckling, popped rivets, etc - which were a sign of the airframe exceeding design limits pointing to near failure and destruction. These a/c were inspected by Engineering officer and most frequently Salvaged Class 26. Don Gentile's Mustang "Shangri La" was an example of the Salvaged Category.

Interesting. I recall the 56th FG at one time having P-47s declared WW with hours ranging from 324.15 to 684.15 hours. If WW was strictly related to time and stress damage was strictly Class 26 then there must have been some type of time modifier. And Zyglo (woohoo) ! I've done Zyglo, but it's been 25 years - lol. That process was invented in 1942 which improved on the older non-flourescent penetrant technique. I am always amazed at how it seems almost all the techniques and tools I use on/with metal at work were developed during WW2.

 

[pbehn]

[QUOTE="chuter, post: 1291082, member: 8848"+ Quote]. I am always amazed at how it seems almost all the techniques and tools I use on/with metal at work were developed during WW2.[/QUOTE]

True of many fields of engineering, I worked in metallurgy which also leapt forward in the war years especially submerged arc welding and impact testing from lessons learned on the Liberty ships.

 

[XBe02Drvr]

thinking about this...they must have abandoned this idea or at a certain number of hours do major overhauls because the B52s have been flying for a LONG time. maybe flyboyj has the answer for that one

I've seen wreckage pieces from two different B-52 crash sites that looked like wing structure and had cracks with patches riveted over them and patches over the patches. Aerolasticity, right? And these were supposedly young airframes.

 

[Airframes]

Interesting statement by Bill, regarding Gentille's P-51 'Shangri La'.
'Legend' has it that the broken-backed wreck was bull-dozed into a pond, and that it might still be there. Was it actually salvaged, in the true sense of the word, as opposed to 'salvaged' meaning scrapped ?

 

[drgondog]

Shangi-La became a hanger queen. Not dumped into a 'pond'