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2022-07 #10 Foreman

Remember the TF39? By now we know that GE made a bunch of them for the C5 Galaxy. We also know it is the father of the CF6-6 and -50 which launched GE into the commercial wide body engine world. We also know that Tinker AFB is a huge Air Force depot for overhauling these engines.


Somewhere in late 1982 I would guess the AF decided that the TF39 turbine mid-frame (TMF) was gonna be outsourced and Ontario won the contract. In the CF6 design there was a long sweeping duct inside the engine between the high pressure turbine and the low pressure turbine contained in a pretty massive case with 6 large struts, a hub, a sheet metal fabricated liner, the rear bearing for the HP system and the front bearing for the LP Turbine. It also was the rear engine mount system.


A little nomenclature - The TMF assembly is what we call an Engine Maintenance Unit (EMU). A basic collection of a section of parts. Along with the LPT EMU and the Turbine Rear Frame (TRF) EMU these make up the LP Turbine "Module" when bolted together. The LPTM is bolted to the rear of the core engine, specifically to the HPT module, which is bolted to the HPC module which is bolted to the Fan module.


Anyhoo - A new shop was set up, in a building not in the big Quonset buildings, pretty much in isolation, to overhaul the TMF for the TF39. I ended up being selected as the foreman for this shop on swing shift. I think Frank ran both the component repair and TMF days. It was good work and it was a smallish crew. Again in the vagaries of Unionism I would have to have several classes of people - Disassembly/Assembly, parts repair, welders. Because of the unique nature of the contract I think there was a hybrid classification made. Unions always like new job classes.


This was my first "management" job. I was no longer subject to union rules as a worker (and no longer paying $25 a paycheck for nothing I wanted) but now I am an adversary of the union - more on that later...


No longer an R27 hourly guy I was an L7 management guy. I think the base pay was like $23,000 a year pretty good money in 1982. It would have been a pay cut from hourly considering overtime but the cool thing about entry level management, and the only way they could fill production jobs was L7 foremen also got overtime! But more importantly the highest R rating at Ontario was like R29, Master machinist or master welder. I had reached a glass ceiling. I think Foreman Frank might have been a level 9 guy after like a 30 year career. Remember GE levels at the time went up to like L18 or something. In these early days of Jack Welch the book on GE was that it was the most mulit-leveled and regimented company on the planet


Bottom line is the the TMF looks pretty simple and in a way it is but there are a lot of parts. The case, struts and hub are straightforward but inside the hub sits a forward and rear sump housing that holds the bearings. This area has to be super precise at the end of the day. On the frame side is the circularity and longitudinal position of the hub rabbets and the sumps themselves are even more precise. Jet engines are oiled in a cool way that requires 6 tubes of oil and air to pass through the struts. For where the shaft passes through the bearings there is a labyrinth seal. Basically a stationary honeycomb seal, against which a rotating knife seal passes, an air gap and then another pair of seals. When this cavity is pressurized any oil wanting to come through the inner seal blows back into the oily "dry" sump.


So there is the obvious oil supply line, at six o'clock there is the oil scavenge line, there is the sump pressurization line, there is a sump drain to drain any oil (should be none to little until the seals are worn out) in the labyrinth. There is a sump vent that carries the pressurization air leaking across the inner seals back to the fan module where it is dumped into the center front of the engine. The air carries a lot of smoky/oily air and inside the fan is an air/oil separator and the separated oil from all the sumps drains through the Fan Frame into an ecology tank. There are usually at least 2 cooling air tubes. In the compressor air is bled off the engine about midway for cooling of lower temperature areas like the outside of cases and at the end of the compressor to cool turbine blades and shrouds. This air is ported into the engine in various tricky ways.


Ecology Sidebar - On the -50 there was something called an "ecology" valve. Radial engines leaked a lot of oil. Turbines leaked a lot less, pretty much zero from the sump drains but on a typical flight a couple of quarts even up to four quarts of oil could be in the ecology tank. Not dumping oil all over the tarmac was good for the survivability of airport gate blacktop. So in 1981 do we drain the ecology tank? Sure. At about 5,000 feet a pressure activated valve opens and we dump a couple or three quarts of jet oil on your neighborhood - LOL. We define "ecology" a bit different these days - LOL.


We used lots and lots of nasty chemicals - we had a gated area in the back of the place with 44 gallon drums stacked about 4 high with spigot valves. When low on MEK or Acetone someone goes about and fills up a bunch of smaller containers. The spigot valves leaked and the blacktop was just sticky goo overlaid with like runway pierced steel mats. We dumped chemical waste pretty much directly into the sewers and the ground.


Airplanes can take off at a much heavier weight then they can land at based on the landing gear structure. If you lose an engine on take off, you are full of fuel and can't immediately land without risking damage to the airplane and at least having to do an overweight landing check. So we circle around your neighborhood at about 5,000 feet dumping tons of fuel on your kindergartens. This still happens today but there is more rigor in finding unoccupied areas and oceans to rain upon. But periodically the nature of the emergency requires an immediate dump and you'll see some story about how bad that airline is. Which leads into a whole topic of image, reputation and safety - Air travel is the safest way to go by far, but when an airplane crashes we do it spectacularly and lost hundreds of souls at once.


I feel necessary to interject how seriously this business takes safety. The record is outstanding. Years ago mount Vesuvius erupted, later mount saint Helen's - When volcanic ash gets into jet engines bad things happen - like all 4 engines quit running. We learned a lot about ash ingestion. We even have standards of how many ppm of ash can be in the air before engine inspections are required. At the Vesuvious event there was a Pratt powered airplane that almost crashed. The press cornered a GE VP - Chip Blankenship - and asked him for a comment about Pratt. He said something great, "In the aviation business we compete for business but we collaborate for safety." and that is true.


Anyhoo working with a small crew in isolation was always better than large shops. I started to become a good team builder identifying people's strengths and weaknesses learning how to motivate them and make them happy workers. At the end of every strut there were end caps bolted on through which the oil and air tubes passed. The tubes were "cut loose" inside the sump and extracted through the end. On assembly they are fixtured with a dummy sump and welded back together which was precise work and I had at a couple of welders on the crew.


Hub diameters getting plasma sprayed and sent for machine, end caps getting polished and deburred. Cases getting heat treated, cracks welded and heat treated again. It was a pretty complete process and shop and we got pretty good at it.


My next lesson was not to dip your pen in company ink...


The TF39 Turbine Mid-frame - my first job as a foreman. I couldn't find an isolated picture so it's a bit of a blurry blow up. You can see the case and liner and a little detail on the bearing arrangements. Later engines will look a lot different as we strive to stiffen the engine, shorten the engine and drive more fuel economy in more thrust in and weight out.


Here is a pretty defining chart on the improvements in air safety from the 70's though 2019. If you think about it, it is truly astonishing. In an earlier post I showed you how passenger loads grew. At the same time as we are growing aviation like hell we are making huge year on year strides in safety. But in context even in 1970 where 3200 people are dying every 621 billion passenger miles. You chance of dying was still pretty slim. Even if you are on a B747 with about 480 of you friends the cumulative probability on an 8,000 mile flight reduces to like 1 accident every 162,000 airplane miles.


Later on I was talking to a bunch of B777 airline pilots. We had an engine issue and one thing we do is talk to groups of pilots to tell them what's going on, what we are doing about it and why they shouldn't worry. I would always show the statistics and say, "So based on you flying 20,000 hours in your career you will never have an engine failure." Instantly a pilot would hold his hand up and say, "I have had two." I took me a while to learn a response to this - it's obviously about statistical variation which is boring to pilots - but a more fun response is, "Outstanding. That's great news for the rest of these guys." and the rest of the guys would laugh.




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More amazing info. I'm not sure if I am correct anymore but I used to imagine that every single safety feature was because someone died. Ice on the wings, loss of all control cables at once, loss of all engine power thus no hydraulics, engines falling off, fires in the cargo bay etc, these all led to fatal air crashes but very quickly after that things were put in place to stop them, eg de-icer boots, triple redundant control cables, APUs, better sim training etc.


You once said something that has stuck with me forever - "It's always the pilot's fault". I said "Sure, but what about Chicago 1979 - the damned engine literally exploded and then fell off a…


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Dan Deutsch
Dan Deutsch
24 jul 2022
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It's everything you said. Late in the series I will talk about being on the "Safety Program Management Team" or Safety PMT. It is a super duper complicated subject and is highly statistically driven.


It works "hand in hand" with the Engineering Red Book. The Red Book is the accumulated knowledge and running rules on every design standard down to the nuts and bolts.


So metal expands under heat. It also cracks to to vibration - which lets call stress. So heat and stress. Another stress is expansion.


We had giant books containing the characteristics of metal. How much does it expand over how much heat. What is the metal's resistance to cracking etc. So if you are going to…


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