Last night, Beege described the latest in a series of very bad news days for Boeing in the wake of the explosive decompression of one of their 737 Max 9 aircraft over Portland during an Alaskan Airlines flight. (If you missed it, read that analysis first.) The fleet of 737s has been grounded at both Alaskan and United and inspections of all the aircraft have begun. Technicians began finding alarming issues almost immediately, with “loose parts” being found in the panels and door plugs of other planes. Making matters worse, it now seems possible that four of the bolts that were supposed to hold the door plug on the Alaskan Airlines flight may have been missing entirely. If so, this was far worse than a simple case of wear and tear leading to a mechanical failure. This is looking like criminal negligence in the maintenance process.

Federal investigators say a door panel slid up before flying off an Alaska Airlines jetliner last week, and they are looking at whether four bolts that were supposed to help hold the panel in place might have been missing when the plane took off.

The comments Monday from the National Transportation Safety Board came shortly after Alaska and United Airlines reported separately that they found loose parts in the panels — or door plugs — of some other Boeing 737 Max 9 jets.

“Since we began preliminary inspections on Saturday, we have found instances that appear to relate to installation issues in the door plug — for example, bolts that needed additional tightening,” Chicago-based United said.

When these types of maintenance shortcomings are discovered, it’s difficult to pin down who bears responsibility. The FAA has ruled that the owner or operator of a commercial aircraft bears primary responsibility for flight safety inspections. But that responsibility is shared with the manufacturer, NTSB, and even the FAA itself. It’s a team effort to ensure that airplanes are as safe and unlikely to crash as is humanly possible. From the sound of these initial inspection reports, the airlines and Boeing have been failing at that task.

For those not familiar with equipment maintenance and operations, it might be tempting to say, “Oh, it’s a couple of loose nuts and bolts. What’s the big deal?” But in reality, it’s a very big deal indeed. Like Beege, I too worked in equipment maintenance and inspections in the military and in private contracting afterward as well. Modern planes are filled with all manner of complex technical systems that allow them to function properly. But they are also mechanical craft filled with all of the usual construction materials required to hold a machine together. Among these are the pieces of steel and other metal that are held together by fasteners and seams of various sorts. These are the literal “nuts and bolts” of the equipment and ensuring they are all doing their jobs is one of the most fundamental aspects of safety inspections.

No matter how you hold two pieces of metal together, it’s never a permanent, “fix it and forget it” operation. Welded seams need to be regularly inspected and even x-rayed to ensure the seams aren’t developing cracks. Nuts do not remain eternally locked down tightly on bolts, even if you are using lock washers, cotter pins, or even industrial adhesives such as Loctite. This is particularly true of aircraft, where all of these elements are regularly subjected to large levels of vibration and wild temperature swings, usually taking place over the course of several flights per day.

All of that hardware needs to be inspected on a regular basis. If those inspections were not taking place or were being conducted in a sloppy fashion, the airlines have been placing the public in needless danger of injury or death. And Boeing shares a portion of the responsibility. We don’t appear to be dealing with a situation where some technicians need to just go in and tighten up a few bolts and return the 737s to service. All of the airlines’ safety procedures should be reviewed before everything returns to “normal.” Where is our Secretary of Transportation in this whole mess? Shouldn’t he be chiming in?