Prior to the true narrative of Boeing Contractor, Lead abuse, I shared with you a few days ago, there was the Horror (Dooror Horror) also provided by Crabby Sparky the EE, cross trained as an aircraft structures engineer.
Airplanes are essentially pressure vessels like an air compressor tank with wings. The tank in this case is held together, and in shape, by the aircraft structure. The frames and stringers all attached substantially to the skins.
The massive moments, compressive stress, tensile stress and shear stress involved in lifting hundreds of thousands of pounds off the ground on the wings are fearsome to understand. Shear is driven into the skins, requiring they be well attached to the structure and also nice and smooth. Meaning no gouges, drill runs, hole tear outs or other sharp features to concentrate stress.
Ground Air Ground (GAG cycles) is a term referring to the take off and climb to altitude (usually 35,000 feet give or take) requiring pressurization of air cabins to 18 psi (Japanese do 20 psi for passenger ear comfort) and then a return at ground level to 1 atmosphere.
Sheets used in aircraft when I was at Boeing were .063 in. thick. It was a BAC and drawing requirement to maintain 2/3 (if I recall) of that thickness to avoid hard spots (too much stress over the reduced cross section). Further the edges of skins are required to be flat, smooth and perpendicular to the lower and upper faces of the skins. I learned all of this in engineering school. EE don’t. This was at that time clearly all spelled out in BAC5300 if I recall. Pretty sure that’s the number.
As an aside, in Kansas several years ago, the Professional Engineering Exams were updated because Mechanical Engineers way out performed the Civil, Electrical Chemical etc., due to the broad and in depth curriculum involved in the BSME pursuit. The only degree harder to attain is Medicine which essentially covers the BSME curriculum with Organic chemistry and the biology of life and organs.
Dick Nott, my supervisor, told me, and I quote: “Just do what they tell you until you get your stamp.” (great training instructions, Dick, especially where none of the leads accepted responsibility) So I went, observed, examined, analysed, wrote dispositions the way I was told, and presented them for approval and a stamp from the certified. The EE was certified. Material Review Board (MRB) Certification required for continuing as an aircraft engineer in Liaison or going to one of the Airlines. The FAA, here, before I explain the horror should, as the flying public also, should, understand the fact that Crabby Sparky had what you claim as certification, to theoretically provide airworthiness, while I did not. Crabby decided what is airworthy. You should all be afraid.
The door: Crabby EE Sparky and I went down to look at a door for the 747 Jetliner. The doors, are pressure rated structure, had an outer skin and an inner skin with a port for the door mechanism. The tag from the computer was sent for irregular skin edges (supposed to be smooth and perpendicular to the skin surfaces (think square edge) as I learned at KU). These had hand ground facets at various angles to include point transitions between these facets. These edges looked like a diamond cutter’s work along the inner skin port edge. OMG!
I said: “These are not good, we can’t accept this.”
Crabby Sparky: “No, these are OK.”
I said: “Aren’t they supposed to be perpendicular and smooth? Look there are sharp spots in the edge.”
Crabby Sparky: “These are OK, we buy them like this all the time.”
I said: “Are you sure these are alright?”
Crabby Sparky: “Yes, I’ll help you write it up.”
So I wrote it up the way he told me as per my instructions from Supervisor Dick Nott and Sparky signed off on the disposition.
The next morning I found the tag sent back with a note from Dan (very good engineer, mechanical) saying: “Mr. Queen when I looked at this door they were knife edged.” They were. Just like I learned in e school and tried to tell Sparky.
Now, thanks to Dan, no knife edged door skins ever left BWAG with my name on the tag.
One wonders how many doors did leave knife edged since Sparky had told me “We (who else did he train?) buy them like this all the time.”
Knife edged doors such as the ones Sparky told me were alright would produce cracking given enough GAG cycles. Once a crack opens it propagates a bit with every pressurization and then depressurization, then again and again. Once the crack reaches maturity the result is catastrophic failure. Sudden decompression (@ 18psi) and ejection of people (keep your seat belt fastened) from the cabin out into the wild blue yonder as happened during Aloha Airlines Flight 243 several years back. GO HERE for the story on Wikipedia. Tomorrow I will be back to the gospel. Coming later this week: “Mad 737 Max Beyond Pressure Dome.” Yes a play on Mel Gibson, Mad Max Beyond Thunder Dome.
Chris Queen. 3/18/2019. That’s all for today. Having a very good time bringing you these truthful disclosures from the annals of the Lazy B. Please hit the Follow key above and to the right for future updates. Please leave me your valued comments below in the form. Please see my books Misquoting Logic (Amazon HERE) and Misquoting Calculus (Amazon HERE).