Aircraft Accidents and Using New Technologies

While investigating an aircraft accident, I interviewed a Required Inspection Item (RII) Inspector in Tennessee; an RII is the second set of eyes to the work performed by the aircraft mechanic, making sure the proper procedures are followed.  He said that part of his normal practice while performing each RII inspection was that he would grip the part’s safety material between his fingers, allowing the sharp safety wire or cotter pin to bite into his skin.  This was his way of dismissing self-doubt, that he had the painful reminder that the installation was properly completed; that the aircraft was safe.

Some mechanics have their own ‘pinch me’ method, a small routine that allows them the peace of mind so they can sleep well at night.  It’s human nature, as well as self-preservation, that drives mechanics to forego that moment forever, the one when an accident investigator shows up at their place of business to inform the mechanic that he may have contributed to the deaths of pilots and passengers by their lack of attention to detail.

Are we, in the maintenance industry, adopting practices that blurs the distinction between ‘being positive’ and ‘pretty sure’?  Although I’m impressed by growing industries, I want to caution mechanics, particularly those coming into the industry, to tread lightly when playing with new toys.

There are articles appearing in Fortune, Aviation Week, Aviation Pros, aka AMT Society and UAS Vision that speak to the new age inspection tool: the Drone.  For someone who conducted visual inspections the old way, let me be the first to say, “I knew it was coming,” and “Are you here to fix the pains of the old ways?”  Allow me to explain.

On April 28, 1988, Aloha Airlines flight 243 suffered a mid-flight departure of the aircraft’s upper crown, a section running width-wise from floor over the crown to the floor on the opposing side; from entry door to wing leading edge; 18.5 feet (5.6 meters) vanished over the ocean.  It was a pivotal moment for every Certificate Holder’s Aircraft Maintenance program and especially their Quality Control duties.  It also forced aircraft manufacturers to reevaluate airframe time limits, particularly for flight cycles.

After this accident/event, structural inspections went into overdrive.  All aircraft structures, especially older aging aircraft, suddenly required zonal inspections called SID (Special Inspection Document) inspections.  The older version of the SID inspection required mechanics to walk the fuselage’s crown from end to end, performing visual and tap inspections along the entire length.

In order to do this, the mechanic donned a harness with straps that wrapped around the chest, back and met at the upper thighs; the mechanic was protected from falling by attaching the harness to an inertial cable tether suspended from a reel on the hangar ceiling.  This tether had one foot of give before it stopped movement, snapping the harness into a zero acceleration (dead stop), thus preventing said mechanic from falling.  With the B727, the crown was accessed by a maintenance stand surrounding the number two engine inlet, two feet above the crown.  If the mechanic stepped down too quickly, the tether would SNAP … stopping downward movement, translating the sudden stop to the harness; the harness would, in opposition to gravity, dig into the mechanic in painful ways at crucial points on the mechanic’s body.  The mechanic would then dangle, suspended until the pain ebbed, thus prompting the title, ‘Dope-on-a-Rope’, hanging like a piñata for all to see.  Pained memories aside, safety is a concern anytime you have someone walking on a smooth surface fifteen to twenty feet off the ground, the chance to easily slip off the rounded crown.

Enter the drone, an independent unit that can hover over the aircraft, even to each side, with developed high-resolution cameras taking incredibly detailed photos.  The applications are endless.  In accident investigating, a drone would be invaluable, able to capture evidence in trees, caverns or cliff faces that would otherwise put humans in hazardous situations to work with.  Even if the drone becomes damaged or destroyed, the consequences are minimal compared to human harm.

Is this what we wish to commit to, locking ourselves into a reliance on drones for our inspection needs?  To me, this is the concern: We are going down a path that may bring us back to where we went off the rails in 1988.

I have been vocal about our industry’s overreliance on technology, to the exclusion of the ‘old ways’.  A drone, just like any tool, has limits to its effectiveness.  When I was a mechanic on the Line, the dawn of digital technology was providing us with a new tool in the way of digital cameras and transmitting the images via phone or computer.  This new tool was priceless; we transmitted pictures of hydraulic leaks or broken restraining hardware, zoomed in, added light or changed the view.  When I was in Tulsa, as part of the American 587 accident, investigators in New York requested I go to American’s hangar to take pictures of a sister A300 airliner’s vertical stabilizer mounts.  For accident investigating, a drone would reduce mistakes while assuring human safety.

What the drone cannot do, however, is hands-on inspecting.  The inspection mistakes leading up to Aloha 243 would have been hampered – not helped – by a drone-like version of inspecting.  In fact, the inspection methods at the time were evolving.  Today, we are suggesting that inspections be performed using technology that further separates the mechanic from the area to be scrutinized.

What does a mechanic look for that applies to a SID inspection?  What tools should he/she use?  The fuselage at Aloha 243’s failure points were considered Pressure Vessel (PV) areas.  PV structure areas are subject to heavy stresses, caused by the airliner skin’s expansion and contraction as the aircraft climbs and descends during each flight.  These large pressurization changes are causing the stresses.

During the time between heavy inspections, the best vantage point to detect these cracks is on the exposed outer skin, as opposed to the inner skin enclosed by the cabin’s furnishings; this is acceptable because the outer skin is exposed.  Even with paint covering the PV, the trained mechanic can detect cracks or corrosion, but it has to be direct eyes on skin, not eyes on drone’s display screens on skin.  There is a reason I say ‘eyes on skin’, as opposed to, say, ‘eyes on metal’.  It is because aircraft of all types are being built with more and more composite materials and, therefore, have different detection methods than metals.

A trained eye can identify subtle signs of metal corrosion below paint that a drone could not, taking into account light, shadows or closeness to the surface.  In addition, a mechanic can check for ‘oil-canning’, a symptom that metal is separating from the structural support members.  The subtle corrosion can bubble below the surface in almost invisible bumps.  To identify these cracks or corrosion, the mechanic must be able to touch the skin, push against the skin or feel the skin for the bumps below the surface.  A drone cannot do this.  The follow up to this discovery would be for Quality Control to perform a Non-destructive inspection method, e.g. Eddy Current, to determine the extent of the damage.

With composite materials, there is a possibility for composite sheet delamination caused by a break in the resin bonding.  A cavity builds between the plies; this then allows water to invade the space between the plies, whether directly by precipitation or by other sources, e.g. humidity.  The water then continues to build.  As the liquid freezes and melts from the extreme temperature variations the skin is exposed to, the composite delaminates further.  These anomalies, invisible to the naked eye (or drone camera) can be discovered using oil-canning inspections or by a tap-test, which identifies the cavity by the change in pitch of the taps made against the skin.  To further test, one would use a non-destructive testing method that would tell if the section should be replaced and how much to replace.

I realize my articles have earned me several titles: ‘Wet Blanket Guy’, ‘Party-pooper’ or ‘That old guy who keeps saying, “Hey, you kids, get off my Lawn.”’  However, I worry that all these new toys will completely replace the ‘old ways’.  Furthermore, the mechanics entering the industry have less access to the old ways as newer inspection methods replace better methods; in the world of cost-savings, newer is often cheaper and more likely to be adopted as adequate.  I’m an old ways guy; I like to touch the repair.  It’s how I know the plane is safe.  Then I can sleep at night.

2 thoughts on “Aircraft Accidents and Using New Technologies”

  1. Steve, as a 40 year aviation safety technician veteran myself, I’m sure I can also be considered in the category known as an “old airplane guy”! I appreciate your articles which are well written based on many years of experience and wisdom. I understand and agree with your professional aerospace safety concerns. While technological advances may have some merit and useful advantages, nothing can surpass the many years of human aviation safety inspection experience which seasoned technicians have known. Their critical keen eyes and hands have probably prevented many mishaps or even disasters from occurring. Thanks for everything you do, and please keep the great work and interesting articles coming! 🇺🇸

    1. Thanks Dave, it’s something all of us ‘old airplane guys’ are doing to give the ‘new airplane guys’ a hand up in the future.

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