Missing The Point…. Missing The Airplane


Missing The Point…. Missing The Airplane

Opinion / Editorial by David H. Marion; Recently, the Aircraft Owners and Pilots Association (AOPA) polled its members and readers of its daily e-newsletter and asked them “what is the most important issue for general aviation in 2018?” Of course, they didn’t really want to know what anyone else thinks so much as with which of their myopically preconceived notions members might agree. (I can’t tell you how many times that has been the case and my own first thought is usually something else completely unrelated to any of their inherently uninspiring poll choices.) The fact of the matter is that they did not allow actual, unrestricted, or original input from their members. Instead, they listed their own narrowly limited list of potential issues and asked us to choose only from that list…

Their choices – and the relative proportion of responses made – were as follows:

  • ATC Privatization – 61.18%
  • Getting younger generations interested in flying aging aircraft – 19.91%
  • Airport access and fees at FBOs – 13.05%
  • Airspace restrictions – 4.22%
  • Other – 2.64%

Here’s what I really think; both the AOPA editors and the majority of their readers missed the boat by a mile… or rather the aircraft. To me, the only valid or significant information in that poll was the phrase “aging aircraft.” Even the bureaucratically cumbersome FAA has enough of a clue to be concerned about aging aircraft, but apparently not AOPA. Maybe if the parts and services for their annual sweepstakes giveaway aircraft weren’t donated and they had to pay full price or actually scrounge for each of them, they’d have a better idea about how onerous and daunting restoring and even just maintaining an aircraft actually is in the real world these days.

Is there anything else more fundamentally important to aviation than aircraft? Along with pilots and sky, that is – you can’t have “aviation” without those three things. As far as I am concerned, nothing else is as fundamental; everything else is basically ancillary. The Montgolfier brothers, Otto Lilienthal, and the Wright brothers were all deeply involved in aviation during its infancy – when it was still in its purest forms, but they did not have any concept of Air Traffic Control, airspace, avionics, liability insurance, Federal Aviation Regulations, or even airports for that matter.

The entire induction air inlet system on a Piper PA-31 Navajo. The darker gold box in the lower right hand corner is the air filter housing. The silver valve assembly is the problematic alternate air valve just before the air enters the turbocharger.

And FYI – although unmanned drones seem to be all the current “rage”, in my opinion they are about as worthless as Microsoft Flight Simulator and neither of them are part of “real” aviation. They are just weak reflections of aviation that miss its point, its reason for being, and they totally fail to capture its true nature and purpose. Drones exemplify the essence of aviation about as well as a black & white television represents the real world. The true nature and purpose of aviation, in my opinion, is to allow humans to soar – in terms of both body and soul. Birds, bats, insects, and even squirrels can fly, but they are not engaged or involved in aviation.

So, quite recently I have been involved with a couple of projects at work (at my “day” job) that illustrate my point regarding the primacy of aircraft – and that, in my opinion, the biggest issues in general aviation in 2018 (or any time) is keeping aircraft airworthy and as affordable as possible – both of which are becoming increasingly difficult and unlikely as time goes on.

One of those work projects was a “firewall-forward” engine overhaul on an old (1976 model) Piper PA-31 series Navajo. The other was an Annual inspection on a 1968 Cessna 310N. In both cases, numerous parts and components were worn out or damaged and needed to be replaced, but some of the necessary replacement parts seem to be no longer available from the OEM’s or from anywhere else for that matter. While Cessna (Textron Aviation) nominally still supports the 310 series, a big part of the problem with the Navajo is that Piper has washed its hands of the type and officially no longer supports it. Just like Microsoft and Windows XP – and that operating system isn’t even as old as those aircraft are.

Close-up of the Piper alternate air valve showing the actuator shaft and its very worn mounting brackets. The assembly at the very top is a magnet that helps to hold the valve closed.

I once had a Director of Maintenance, under whose supervision I worked for many years, accuse me of “always wanting to make an old airplane new again.” I’ll gladly own up to that charge – it’s true. Just like Scotty on Star Trek, my idea of fun and relaxation is to study technical manuals (albeit for aircraft, not starships.) So too, one of my biggest fantasies is to be able to do my own aircraft major restoration project like my friends Addison and Ryan Pemberton in Spokane, Washington did with their 1942 Grumman JRF-6B Goose.

I expect however that 98% of aircraft owners do not have the initial desire much less the technical and monetary resources to do something like that with their own aircraft – even if those aircraft are significantly newer than the Pemberton’s Goose. For that other 98% however, it is not unreasonable for them to expect to be able to obtain all of the parts that they need to keep their aircraft airworthy. Unfortunately, it is increasingly becoming the case that they cannot. Or if the parts are still available, they cost an absolute fortune.

On the Piper Navajo that I mentioned, one of the problematic parts was the fiberglass and aluminum air duct assembly between the induction air filter housing (which is built-in to and part of the cooling baffles) and the turbocharger. That duct assembly incorporates an “alternate air” valve in case the inlet filter somehow gets blocked or clogged. It is comparable to the carb heat valve on a carbureted engine, which can suffer blockage from ice accumulation in the carburetor’s venturi.

The Cessna alternate air valve assembly which functions as an end cap for the main induction air filter housing. The smaller port on the lower right is where the ducted “alternate air” enters the air filter housing when the valve is open. When closed, it dumps out the notched cut-out.

When activated by the control cable coming from the cockpit, the alternate air valve opens, bypassing the normal air filter and allowing raw, unfiltered air to enter the turbocharger and the rest of the engine’s induction system. The control cable attaches to a lever arm which rotates a simple shaft and cam assembly, which in turn pushes against and opens the valve door itself.

The door is normally held closed by a magnet. In this particular case, the hinges or pivot brackets for the control arm were so worn out that the shaft assembly literally rattled in place. The shaft was worn down to about 80% of its original diameter and the pivot holes in the triangular mounting brackets were egged out to something like 150% of their original dimension. Neither individual repair parts nor a whole replacement duct assembly are still available from Piper from what we have been able to determine.

Our parts department staff contacted all of our usual, “approved” aircraft parts sources without any luck. They also researched specialty component repair shops (Certified Repair Stations) and eventually found one – just one in the whole country – who claimed that they could repair the old, worn out “core” duct assembly that came off this particular aircraft… (wait for it) for the price of $2,000 USD and with a 10-week lead time for turnaround.

Now any competent, even non-aviation oriented, machine shop could fabricate a new arm and shaft assembly and new mounting brackets out of basic steel stock, but the FAA rules for going to someone like that are a bit complicated. (Ref. FAA Advisory Circular AC 23-27 for example.) As a mechanic, I could fabricate the parts myself in order to patch or “repair” the duct assembly, but I could not “sell” any such repair parts that I fabricate like that. I also do not have as much capacity to work with or fabricate steel parts like these from raw stock materials as I do with typical aircraft-grade aluminum sheet metal parts.

Close-up of the worn out control arm, shaft, and bearing assembly – in which there are no more needle bearings. It was so worn and sloppy, they all fell out.

As a professional aircraft mechanic, I am also not allowed to go to a non-aviation machine shop and get them to make the necessary parts for me – but the aircraft’s owner could. He still can’t sell any such parts to someone else, but as long as he is somehow directly involved in the process by contracting with them, providing them with technical specifications, design guidance, or whatever, it is legal for him to get someone like that to fabricate the parts for installation and use on his own aircraft.

But of course, neither the aircraft’s owner nor I (nor any other mechanic really) commonly has access to any formal specifications or blueprints (i.e. “approved data”) for the original “certified” parts like those. The best we could do is to use our own judgment and common sense to copy them based on what we see or can measure ourselves. To some inspectors at the FAA, that would be reasonable, but to others maybe not so much.

On the Cessna 310N in question, coincidentally quite similarly too, one of its own alternate air valves was a worn out piece of junk as well. On the Cessna, the engine’s induction air filter is housed in a canister-like assembly in the back of the engine compartment. It is fed with fresh air from an intake built-in to the leading edge of the wing inboard of the nacelle. The main induction air flows through a flexible duct in the wing to the engine compartment and the filter canister before being fed into the engine.

The alternate air however is fed through a smaller duct to the same canister, but it originates from a circular flange on the cooling baffles behind the no. 1 cylinder on the engine itself. The alternate air control cable from the cockpit attaches to a lever at the end of a shaft which penetrates the end cap assembly of the canister. The end cap assembly can be removed to permit replacement of the air filter inside the canister.

The alternate air valve itself, at least as originally designed and installed on this version of the Cessna 310, is a curved, rotating panel arrangement mounted on and offset from the core rotating control shaft of the alternate air valve. The whole valve is supported in the end cap of the canister by a single roller bearing assembly riveted to the center of the end cap.

These 2 photos show the range of slop in the valve; the green box shows the valve seated and the green line the normal orientation of the control shaft. The red box shows the valve unseated even in the closed position and the red line the angle at which the shaft falls out of proper alignment.

Follow all of that so far? Because of the weight of the steel valve and its leverage against the pivot bearing, they both eventually wore out. It is obvious that at some point, the damage was so excessive, the little, individual roller bearings fell out of the main bearing assembly housing – leaving the control shaft to rotate and slap loosely against the not-so-smooth bearing frame. (In my professional opinion, this problem is something that should have been noticed, caught, and rectified years ago; it is that bad!)

This original alternate air valve assembly was so problematic for Cessna that they eventually (and actually long ago) designed and put out a whole different design to replace it. The replacement air filter housing and integral alternate air valve came in the form of Service Kit no. SK402-27. In place of the ducted air entering through the curved valve in the side of the end cap assembly, they installed a relatively simple, flat, butterfly valve in the center of a whole new end cap. It allowed ambient, unducted air from the surrounding engine compartment to enter the air filter canister when the control was activated.

Even so, this particular aircraft is now 50 years old and it was never modified with the new-style alternate air valve, so even the idea of repair parts for the old, original curved, side-ducted alternate air has faded into the mists of ancient history. Even more unfortunately, the new-style alternate air valve assembly in the form of SK402-27, or even individual component parts thereof, are equally no longer available as well. And even if they were, the price that I saw quoted from one source (in spite of the fact that it is not even available at any price) was for $1,836 USD.

Note that although it is almost never “mandatory” to replace parts in accordance with a Service Bulletin or Service Kit, unless they are incorporated into or referenced by an Airworthiness Directive of course, aircraft owners ought to keep in mind that 20 years down the road, after those repair or modification parts are even more scarce and harder to come by, the price most likely will have skyrocketed tremendously. You are almost always better off getting and installing them sooner rather than later – especially if they fix a problem and prevent eventual collateral problems.

These 2 photos show the interior view of the Cessna alternate air valve in its proper orientation (in green) and the degree to which its worn out shaft and bearing allow it to fall out of position (in red.)

Nothing about this current parts cost and availability situation should be considered acceptable – to the FAA, to aircraft owners, or to mechanics and repair shops. We’re talking about relatively simple metal structures that are easy to fabricate for anyone with basic machining or manufacturing capabilities. Even in terms of “economies of scale” for limited aircraft production numbers (at least as compared to automobiles for example) or in terms of product liabilities issues, that is still outrageous to me.

One of the biggest initiatives by the FAA in recent years has been to alter the paradigm of formal certification under Part 23 for new parts and even whole aircraft designs. It went into effect only as recently as last August 2017, so there really has not yet been enough time to be able to assess its impact on the industry. I do feel however that even without a crystal ball, I can easily foretell that general aviation will never be so affected by the issues of ATC privatization, airspace restrictions, or FBO fees as it will by a lack of active pilots, young or old.

Even beyond that issue however, general aviation won’t survive a lack of airworthy and affordable aircraft. With new aircraft costing 10 to 20 times or more than old ones, the brunt of the load of the basic existence of general aviation will continue to be carried by older aircraft. At least until the cost and scarcity of parts to maintain them forces them to be grounded and retired or scrapped. I think that should be a major concern to everyone involved in the industry.

Dave Marion is the Technical Content Editor at Seaplanemagazine.com. As A&P and IA with 30 years of experience in aircraft maintenance, he is also a Commercial Pilot with Airplane, Single & Multi-Engine, and Instrument ratings. He has a BA from Colgate University in 1984 and also graduated cum laude from Embry-Riddle Aeronautical University (DAB) with a BS in Aviation Technology in 1990. He can be reached along with all of the editors via E-Mail: [email protected]

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