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Keeping it Clean!

Cleaning your Aircraft or Not?

Quite often I think about these articles just after having a repetitive experience and would like to share with others to either explain why Maintenance Operations find this necessary or to help Owners-Operators maintain their Aircraft in better working order.

Let’s start out with FAA Regulations regarding an Annual-100 Hr Inspection. You can find a reference to this Regulation on the FAA Website at this location:

Item #1 Scope and Detail of Items to be Included in Annual and 100 Hour Inspections

(a) Each person performing an annual or 100-hour inspection shall, before that inspection, remove or open all necessary inspection plates, access doors, fairing, and cowling. He shall thoroughly clean the aircraft and aircraft engine.

I underlined the cleaning process as this is likely one of the most overlooked items I see on any first time Annual Inspection or new-to-me maintenance Aircraft I have ever come across. So let’s discuss why the importance of such during Inspection.

The most obvious has to do with structural integrity. How does one look at an Airframe for working rivets or crack propagation when there is a 40 year old layer of debris beneath the sub-floor. On retractable gear Aircraft this will mask any hydraulic Fluid leaks and same can be said for oil leaks on an Engine. For such neglected Aircraft some would consider this a positive since it keeps leaks sealed & contained. Worst case conditions it will mask an important or even critical issue therefore for the preventative maintenance conscience minded individual, it presents a problem. Those pro-active minded individuals prefer to be alerted in advance prior to component failure.

When I started working on this article I had an Aircraft in mind that prompted this writing initially. I just recently had another Aircraft in where I did some rather evasive maintenance and discovered several un-airworthy items. This was not an Annual Inspection however a poorly maintained complex, high performance, 6-seat Aircraft.

With only 5 Flight hours from departure after the heavy maintenance they landed for Fuel only to discover oil dripping beneath the Aircraft just aft of the Engine Compartment. FaceTime is next best thing to having a Mechanic on the spot! Turns out the oil was actually a mix of heavy concentration of dirty belly oil & exhaust residue mixed with Fuel that was washing the contaminants loose during Flight. After checking a few areas in Engine Compartment that were recently worked on calibrating the fuel system it was determined that a main fuel line going from fuel selector to auxiliary fuel pump was failing from age & deterioration. This was a 1975 OEM Fuel Line still installed and never looked at during Annual Inspection.

  • Proper Inspection

  • Proper cleaning of sub floors would have found this Fuel Staining prior to failure

The third example here was a T210 just days ago that started out as a stranded Pilot at the Fuel pumps with a weak battery. I opened the Engine cowling to access battery compartment initially & look for anything abnormal that would cause the main battery to fail. Finding the electrolyte level absent was a pretty good indication of the problem at hand however the fresh & old exhaust staining covering the heat exchanger was a much more concerning matter than the pressing battery issue. The amount of Exhaust staining was an immediate alarm. Further examination revealed this was cumulative staining over time and this should have certainly been addressed much sooner than it was. Again, a clean Engine compartment would have shown this clearly needed maintenance action. Unfortunately, the signs were likely present at the last Annual Inspection and should have been addressed at that time.

Corrosion will cause degradation over long term exposure to elements without protection. Oil leaks and filthy bellies are not considered “proper” corrosion protection! That 40 year old accumulation of debris could and will hold moisture & byproducts that can remain hidden until expensive repairs are needed. Under the worst of circumstances corrosive elements will continue to deteriorate all the way to failure or very expensive rework is required.

A properly cleaned and maintained Aircraft will show any early signs of fluid leaks be it Hydraulic, Fuel or Oil. Concerning the Aircraft structural integrity, maintaining a clean Aircraft will allow early detection of deficiencies and crack propagation. This alerts the maintenance crew to address these issues before there is a “real” problem and Aircraft is grounded or worse. Some of these various leaks are acceptable when closely monitored till maintenance items can be addressed, parts can then be ordered in advance if needed. This also allows preparation for service work at a later date when Flight Schedule permits or at a more convenient time-frame timed at an upcoming maintenance event. The same mindset can be said for structures and minor cracks in non-critical areas that can be stop drilled to prevent further development.

Cost savings can be attributed to maintaining a clean Aircraft.

I recently went through an Annual Inspection where the exterior had likely not been washed in the previous 12 month since last Annual. If you receive your Aircraft after an Annual Inspection and there is a significant color change in appearance then this certainly applies to you as an Owner-Operator.

There is no way to properly perform an Annual Inspection on any Aircraft without cleaning it thoroughly. Several hundred hours of operation and oil dripping off the under-belly will require at least 2-individuals and 6-8 hours of cleaning generally on any single engine complex Aircraft.

If you allow food and drinks in the Aircraft especially those with small children and it is treated like an unkept mini-van throughout the year expect an additional ½ day of labor in Cabin cleaning alone. Cleaning the gummy-bears out of the seat tracks and corrosive soda spills from under the sub-floors takes up Shop Labor man-hours better spent maintaining the Aircraft for a faster turnaround time out of scheduled maintenance. When I am doing a November Annual and I lift the Carpet to find corn-chips, popcorn & Christmas cookies I can at least date those cookies to appx 11 months of undisturbed sitting & deteriorating.

I am not telling every Owner how to Operate or Maintain their “Magic Carpet Ride” throughout the year. What I am suggesting is that come Annual-100 Hr Inspection it is time to look at your Aircraft as an Aerospace Machine and preparing it for continued service without issue hopefully through next Inspection Schedule. How your Aircraft is maintained and kept between the inspection intervals determines how much time is spent during the scheduled service & inspection events.

A properly maintained & clean Aircraft with corrosion treatments will nearly last indefinitely. Aging Aircraft is a real issue today and dependent upon how these older Aircraft are maintained will determine how long they will remain in service and indirectly reflect the operating & service cost throughout the year.

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