The Problems of Keeping Older Aircraft Airworthy

Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules

MIflyer

1st Lieutenant
6,600
13,115
May 30, 2011
Cape Canaveral
My first job after college was a USAF mechanical engineer at Oklahoma City Air Logistics Center, Tinker AFB, OK. A big part of our work was keeping "Older" aircraft flying, and at that time Older meant 15 to 20 years, late 50's to early 60's hardware. Even at that time we had problems with companies that had produced hardware for airplanes like the F-106 having gone out of business or bought out by other companies, and technical data lost or incomplete. For example, the F-106A had a switch that automatically transferred fuel when the fighter went supersonic, retrimming the airplane when the center of lift moved aft. It was a very reliable little piece of 50's technology, and a consequence of that was we did not buy parts to repair it or even know how to fix it. The company that held the tech data admitted they were missing the data required to make the parts and suggested substituting an electronic box that they had developed to fix the post stall gyration of the A-7D. Unlike the older gear it used solid state transducers instead of bellows and integrated circuits to detect when the airplane got to mach 1.05.

Then there was the F-106 cooling turbine, the most complex one around and also the least reliable. We started a project to see if we could substitute an F-4 cooling turbine.

I did have to "design" a part for the H-19 helicopter. It seems some of our allies were still flying them. The "design" process consisted of getting a part out of supply and making a USAF drawing of it.

The thing was, we had teams working in pneumatics, hydraulics, electronics, structures, etc, as did the other Air Logistics Centers for the aircraft they were responsible for. We examined failed parts to detect possible problems and areas for improvement We supported Mishap Boards. We looked at ways to reduce costs. One day we all but grounded the entire F-105 fleet when, after a fatal mishap, we found that some genius at OC-ALC had decided to stop time compliance change outs of the Auxillary Fuel Tank Pressure Regulators beacuse it was "Too Much Trouble" to do so. So we had an unknown number of those regulators that might just be about to blow up an airplane. And one day we grounded ALL of the KC-97's from further operations and sent them to the boneyard because one of the oldest engineers found out that there was a severe corrosion problem with the landing gear attach points.

Now, for the WW2 warbirds, 80 years old rather than 15 or 20, who is doing that ALC job? Nobody! Individual shops may be looking at things they know about but NO ONE is surveying the whole remaining fleet and trying to anticipate what might occur and what might be done to fix it.

I have found out that for my 1946 Ercoupe new 5.00X4 nosewheel tires now cost $650 each. I am looking into modifications to enable the use of the far more common 5.00X5 nosewheel tires, but since that has implicatons for the whole landing gear it will take some engineering work to implement.
 
My first job after college was a USAF mechanical engineer at Oklahoma City Air Logistics Center, Tinker AFB, OK. A big part of our work was keeping "Older" aircraft flying, and at that time Older meant 15 to 20 years, late 50's to early 60's hardware. Even at that time we had problems with companies that had produced hardware for airplanes like the F-106 having gone out of business or bought out by other companies, and technical data lost or incomplete. For example, the F-106A had a switch that automatically transferred fuel when the fighter went supersonic, retrimming the airplane when the center of lift moved aft. It was a very reliable little piece of 50's technology, and a consequence of that was we did not buy parts to repair it or even know how to fix it. The company that held the tech data admitted they were missing the data required to make the parts and suggested substituting an electronic box that they had developed to fix the post stall gyration of the A-7D. Unlike the older gear it used solid state transducers instead of bellows and integrated circuits to detect when the airplane got to mach 1.05.

Then there was the F-106 cooling turbine, the most complex one around and also the least reliable. We started a project to see if we could substitute an F-4 cooling turbine.

I did have to "design" a part for the H-19 helicopter. It seems some of our allies were still flying them. The "design" process consisted of getting a part out of supply and making a USAF drawing of it.

The thing was, we had teams working in pneumatics, hydraulics, electronics, structures, etc, as did the other Air Logistics Centers for the aircraft they were responsible for. We examined failed parts to detect possible problems and areas for improvement We supported Mishap Boards. We looked at ways to reduce costs. One day we all but grounded the entire F-105 fleet when, after a fatal mishap, we found that some genius at OC-ALC had decided to stop time compliance change outs of the Auxillary Fuel Tank Pressure Regulators beacuse it was "Too Much Trouble" to do so. So we had an unknown number of those regulators that might just be about to blow up an airplane. And one day we grounded ALL of the KC-97's from further operations and sent them to the boneyard because one of the oldest engineers found out that there was a severe corrosion problem with the landing gear attach points.

Now, for the WW2 warbirds, 80 years old rather than 15 or 20, who is doing that ALC job? Nobody! Individual shops may be looking at things they know about but NO ONE is surveying the whole remaining fleet and trying to anticipate what might occur and what might be done to fix it.

I have found out that for my 1946 Ercoupe new 5.00X4 nosewheel tires now cost $650 each. I am looking into modifications to enable the use of the far more common 5.00X5 nosewheel tires, but since that has implicatons for the whole landing gear it will take some engineering work to implement.
I love the techie techie talk. Certainly of older days. Please continue.
 
I agree fully with your comments that no one is doing a fleet wide analysis of defects on warbirds and worse still when a warbird owner/maintainer finds a problem with their aircraft they never, or almost never, report it to the FAA SDR system so that others can learn from their experience.

Shared knowledge is the greatest safety tool in aviation. Many improvements and AD's come from the SDR database and most new regulations come from problems that have been learned the hard way.

I have been a firm believer in the SDR system since 1967 when I was doing an annual on an early Cessna 172. I had just learned about the SDRs as part of getting my A&P and so had a quick look through the latest few issues and there was one about tailplane front spar cracking caused by pilots sitting on the tailplane to get the nosewheel off the ground for moving around hangars and tarmacs. I checked the aircraft I was inspecting and holy shit - it had a cracked spar that could only be found, as the SDR said, with a mirror and strong light. Naturally I reported it, along with many others who found the same defect, and an AD followed soon after which eliminated the problem.

That SDR booklet possibly saved my life, and/or the lives of others who used the same aircraft.

Over the years I have found a number of other problems from the SDR booklets and web pages.

The other problem is that some aircraft have design features that can cause long term issues. Some have cavities that are not drained or ventiated so that condensation collects and causes corrosion.

Others have complex components that cannot be visually inspected for corrosion. Look at the Spit mainspar as a perfect example Multiple tubes of various lengths rammed one inside the other with a solid block rammed in last and then the whole thing bent a short distance from the attach bolts. How do you inspect that for corrosion - especially where the many bolts pass through it (with modern electronics it is actually relatively easy to inspect but the cost of the inspection is not cheap and the person doing the inspection really needs to know what they are doing or they will miss defects). How do you inspect it for stress cracks in the bent section? Several ways but again not cheap.
 
Last edited:
Others have complex components that cannot be visually inspected for corrosion.
A friend of mine was killed at Edwards AFB i the early 1980's when the Douglas B-26 they were using as a Control Configured Aircraft (programmable flight controls) lost a wing. The cause was a manufacturing defect that had occurred when it was built in 1944. I do not know if that defect could have been found without extensive dismantling.
 
That is actually not hard to find with modern tech like I believe needs to be used on Spitfire spars and a lot of other components in various aircraft. Way back I was involved in replacing a main gear pivot housing on a DC-9 which was detected by NDT to have cracks in it. A known problem on Srs 30 freighter aircraft.

They recently replaced a LH outer spar cap on the Beaufort being restored at Caboolture here in QLD because the NDT on the wing spar found an inclusion (air bubble) in the extrusion.

The problem with a lot of these tests is you need a sample for the technician to train on. Fortunately the Caboolture crew had several spares.
 
Last edited:
Slowly.

Tearing that wing apart after it was almost finished set it back a fair while and several of the volunteers have fallen off the perch.

These photos are from a couple of years ago. I should have a lot of more recent ones but I cant seem to find them, Might be getting old..

1718525811685.png

1718525890758.png


1718526003180.png
 

Users who are viewing this thread

Back