Over 16,000 Cessna 172K, L, M and N models left the factory in the 1970s. Most of these Skyhawks are still flying, and they’re gaining value, too.
The Cessna 172 is the most successful General Aviation aircraft model of all time. It has weathered the storms of inflation, recession, crushing product liability lawsuits, and dwindling demand.
The 172 was certified Nov. 4, 1955. A premium version called the Skyhawk was first sold alongside the standard 172 in 1961. The Skyhawk came with upgraded avionics and appearance packages.
Four variants of the 172, the K, L, M and N models, and several modifications would take the 172 from 1970 through 1979.
The 172K, L and M variants all came from the factory with the 150 hp, four-cylinder Lycoming O-320-E2D “Blue Streak” engine. The N model was powered by the 160 hp Lycoming O-320-H2AD.
Certified May 9, 1968, for the 1969 model year; 2,062 produced.
In 1969, the 172 had been upgraded with larger rear side window. Additionally, the rudder was fitted with a ground-adjustable trim tab at its base. In 1970, “drooping” conical-cambered fiberglass wingtips were added to the K model.
Certified May 13, 1970; 1,535 produced.
In 1972, tubular-strut landing gear replaced the Wittman sprung-steel type gear. This change increased the footprint of the landing gear by 12 inches. The dorsal fin was lengthened to run the length of the fuselage to a point just behind the rear windows.
Certified May 12, 1972; 6,825 produced.
With the M model, additional leading edge camber/droop was applied to the wings. This new wing was called the Camber-Lift wing and promised improved low-speed handling characteristics. Tinted skylights in the ceiling were offered as an option.
In 1974, the Skyhawk II trim package was added to the lineup. According to a Cessna marketing brochure from 1975, the Skyhawk II combined “…the businesslike blend of performance, economy and comfort [of the Skyhawk] with the nine most-wanted Skyhawk options.”
The brochure lists those nine options as: “Cessna Nav/Com with 360 channels for communications, and 160 for navigation with VOR indicator, Dual Controls, Emergency Locator Transmitter, Pitot Heating System, Alternate Static Source, Omni-Flash Beacon, True Airspeed Indicator, Navigation Light Detectors, Courtesy Lights.”
Certified May 17, 1976; 6,427 produced.
In 1976, Cessna stopped marketing the aircraft as the 172 and began exclusively using the Skyhawk designation. The “Skyhawk/100,” as Cessna called it, was introduced for the 1977 model year.
The “100” moniker indicated that the aircraft was powered by a 160 hp Lycoming O-320-H2AD engine designed to run on 100LL. The previous O-320-E2D could run on 80/87 Avgas.
A Cessna dealer sales notebook lists increases in performance nearly across the board for the 1977 172 over the 1976 model.
In 1977, in-flight-adjustable rudder trim was available as an option, and pre-selectable flap control came standard. In 1978, a 28-volt electrical system was installed. In 1979, the flap extension speed was increased to 110 kias.
The 172 continued to roll off the assembly line in the 1980s, until production was halted in 1986 due to unprofitability driven by onerous product liability lawsuits. The passage in 1994 of the General Aviation Revitalization Act (GARA) did indeed revitalize the General Aviation industry. Cessna began producing Skyhawks (and other aircraft) again in 1996. The Skyhawk continues to be produced today.
In fact, as of this writing, the Cessna 172 may be more popular than ever. In an August 30, 2018 report from AOPA about the current hot market for used aircraft, the 172 is mentioned for its recent rapid appreciation (see link below).
“Prices for 40-year-old airplanes do not typically jump 20 percent in the space of a few months, but that’s exactly what’s happened to Cessna Skyhawks produced between 1968 and 1976.”
The report continues, “Rodney Martz, a senior aviation technical specialist in AOPA’s Pilot Information Center, said the recent jump in sale prices for Skyhawks produced in the 1960s and 1970s stands out as the largest percentage increase he has seen in many years, if ever.”
That, as we would say in the 1970s, is a really “far out” achievement.
Jennifer Dellenbusch is president of the Cessna Flyer Association. Send questions or comments to .
As an aircraft owner and pilot, you can legally perform some maintenance tasks, but you must adhere to strict guidelines when doing so. Steve Ells walks us through packing wheel bearings, while highlighting what’s important to stay legal.
As most readers of Cessna Flyer know by now, all aircraft maintenance tasks must be overseen or performed by an appropriately-rated person. For maintenance tasks, this means an A&P mechanic—or a technician, as some like to be called these days—is frequently both performing and signing off on the work. This mechanic must (by regulation) have up-to-date versions of the appropriate manuals, bulletins, tools and equipment necessary to complete the tasks.
However, there are also a number of maintenance tasks that owners may legally perform. These are termed preventive maintenance (PM) tasks. There’s a long list of them in Appendix A of FAR 43.
What is considered preventive maintenance?
Appendix A is titled, “Major Alterations, Major Repairs and Preventive Maintenance.” Paragraph (c) lists preventive maintenance tasks. Type “Appendix A of Part 43” into your favorite search engine (or find the link in Resources on Page 35. —Ed.).
There is a surprisingly long list of tasks allowed. For instance, owners are permitted to remove and replace batteries, replace bulbs, reflectors and lenses of position and landing lights, and replace prefabricated fuel lines.
They can also remove and replace panel-mounted communications and navigations receivers and update databases in panel-mounted avionics such as GPS navigators.
Great news, right? It is, especially if a pilot has the time and a place to do these tasks. The potential for saving money exists, but much more important is the satisfaction to be gleaned from learning how to take care of your own airplane. (For further reading, see the sidebar on Page 34. —Ed.)
Are you permitted to perform preventive maintenance tasks?
FAR 43.3 paragraph (g) says that “…the holder of a pilot certificate issued under Part 61 may perform PM on any aircraft owned and operated by that pilot which is not used under Part 121, 129 or 135 of this chapter.”
So, according to this section, if the owner and pilot is not using his airplane for hire, whether on a scheduled service, an on-demand service or as a foreign carrier operating for hire in the U.S., he/she can perform PM.
But there’s a catch. It’s in 43.13. It’s titled “Performance Rules (General).”
43.13 Performance Rules (General)
The following three points—from paragraphs (a) and (b) of the performance rules—have been abbreviated to simplify the important points the maintenance performance rules for owners.
1. Each person performing maintenance, alteration, or preventive maintenance on an aircraft, engine, propeller, or appliance shall use the methods, techniques, and practices prescribed in the current manufacturer’s maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques, and practices acceptable to the Administrator.
2. He shall use the tools, equipment, and test apparatus necessary to assure completion of the work in accordance with accepted industry practices.
3. Each person maintaining or altering, or performing preventive maintenance, shall do that work in such a manner and use materials of such a quality, that the condition of the aircraft, airframe, engine, propeller, or appliance worked on will be at least equal to its original or properly altered condition (with regard to aerodynamic function, structural strength, resistance to vibration and deterioration, and other qualities affecting airworthiness).
In other words, if you’re going to do PM, you must follow the procedures in the manuals. It’s as simple as that.
It’s important at the outset to understand that airplane maintenance, while seeming to be like automobile or other gas engine maintenance in that it must be done right, is different in a very important way. In airplane maintenance, there is a published protocol for every operation, even the tightening of a nut or bolt.
Another peculiar-to-aircraft trait is this: the strength versus weight equation must always be kept at the forefront of every operation and decision. In other words, if you believe that more is better, whether it be the size of a bolt or the amount of torque, you’re going to do more harm than good.
Gathering the manuals and bulletins to meet the requirements of the FARs is much easier and less expensive than it used to be. The secret is the internet. Manufacturers have come to realize that making their manuals and bulletins available at no cost or consolidating a double-shelf full of manuals onto a CD is a sound idea, simply because access to manuals makes it much easier for maintenance shops (especially smaller shops) to access the precise methods and techniques the manufacturer has developed for maintaining its product.
So, step one for owners that want to start working on their airplanes is to have or have access to manuals, and either have the tools or be able to manufacture the tools required to properly perform each maintenance task.
Let’s look at an example of why manuals are important.
Greasing wheel bearings: a “simple” preventive maintenance task
Greasing the wheel bearings on an airplane may seem simple. At its most basic, it can be described in the following steps: First, jack up the airplane or axle enough to get the tire off the ground, then remove the axle nut and pull the wheel/tire assembly off the axle. Next, remove each bearing, clean it and the bearing race, inspect for damage or corrosion, replace if necessary, pack with grease and reinstall. Finally, reinstall the tire/wheel assembly, tighten the axle nut and lower the tire to the ground.
Not so fast. There’s more to it. In fact, there’s quite a bit more.
To remove the tire/wheel assembly (TWA), the brake assembly must be partially disassembled. This disassembly requires the removal of two or four bolts to release what’s called the brake back plate(s). The TWA can be removed only after the back plate(s) have been removed.
Assuming the airplane has been jacked up far enough to lift the TWA, a large cotter pin must be removed prior to removing the axle nut. Then, the TWA can be pulled from the axle.
There is an inner and an outer bearing. From the earliest parts manuals, Cessna breaks out the parts in wheel assemblies. The bearings are always referred to as cups—often called the “race”—and cones—which are often called the bearings.
Here’s another thing to know that is hard to find in any manual: Bearings and races are matched pairs. Don’t take the bearing assembly you removed from the race on the valve stem side of the TWA and install it in the race in the non-valve stem side of the TWA.
What grease to use?
Pre-1962 Cessna single-engine service manuals suggested that wheel bearings be cleaned and greased at the first 100 hours time-in-service, and thereafter at 500-hour intervals, unless operated in extremely dusty or sandy conditions.
The manual specifies MIL-G-25760 grease. However, there’s also a sentence that says that the military specifications are not mandatory, but are listed to serve as a guide. It goes on to say that most products produced by reputable manufacturers meet or exceed these specifications.
Later Cessna manuals give a different MIL-SPEC number, but cite “general purpose grease.”
I personally like the 500-hour greasing interval. Unless I’m performing maintenance on an airplane for the first time, that’s the interval I use.
Cleveland, the manufacturer of brakes and wheels used on Cessna singles, suggests the use of Mobil SHC™ 100 grease.
Bearing removal, cleaning and greasing
After the TWA has been removed, the bearings are removed. This usually requires the removal of a snap ring, a washer, a felt grease seal and another washer.
Bearings are then cleaned with Stoddard solvent, applied by either an air-powered solvent sprayer or a brush. Air can be used to blow the grease out, but never spin a bearing by directing compressed air perpendicular to the rollers.
Directing a stream of air across—not between—the rollers in roller bearings is dangerous because the bearing cage is designed only to maintain the spacing between the rollers. It’s not strong enough to contain the rollers when they rotate at a high rate of speed; in other words, directing air across when bearings can result in fast-moving projectiles.
After the bearing is clean and dry, look for corrosion and/or pitting. If found, replace the bearing and matching race.
Bearings are repacked by putting a gob of clean grease in the palm of either hand and forcing the grease up into the bearing. Press the bearing down into the grease until the bearing comes into contact with your palm. Repeat this procedure until grease appears at the top of the bearing cage.
You can also buy a bearing packer and use it to pack the bearing. Look up “wheel bearing packing tool” on your favorite search engine. YouTube also has wheel bearing packing videos. (See Resources for an additional article that discusses wheel bearing service. —Ed.)
The last step is to look at the grease seals. For decades, Cleveland, the manufacturer of most GA wheels and brakes, has used felt pads to seal against sand and fine dirt. These seals are inexpensive and work well.
Recently, Cleveland has replaced the felt pads with molded rubber grease seals. These may be used in place of the felt seals.
Putting it all back together
The newly-greased bearings are reinstalled in the side of the wheel which they came from. Slide the TWA onto the axle. If it doesn’t slide all the way on, you’ve got the large steel washers on each side of the felt seal in wrong. Swap the washers around until the TWA slides all the way onto the axle.
Thread the axle nut onto the axle.
How tight should it be? I couldn’t find definitive information on how tight the axle nut should be. Field experience suggests to tighten the nut up well to seat the bearings, then loosen it until you can feel a slight movement of the wheel in and out on the axle, then snug it back down until the TWA spins without resistance and no in-out movement is felt.
Now, to reassemble the brake. Two or four bolts were removed so the back plate could be removed to free the brake disc from the inner and outer brake pads.
Whenever I have a TWA off the axle, I clean up the brake guide pins with a Scotchbrite pad. I also clean the guide pin holes in the torque plate. These guide pins must slide in and out to allow the brake to self-adjust as the brake pads wear.
The devil is in the details
The last step is often missed as it’s not in the Cessna manual. It’s found in the Cleveland Wheels and Brakes Component Maintenance Manual, Appendix A titled, “Wear Limits and Torque Values.” This manual, and all of the Cleveland wheel and brake manuals, are available for free on the Cleveland website. Start by downloading the Technician’s Service Guide. (See link in Resources. —Ed.)
This critical step in reassembly is applying the proper torque to the two or four back plate tie bolts. Overtorqueing the bolts can deform the brake housing.
The proper torque on almost every Cessna single engine brake is 75 to 90 inch-pounds (6.25 to 8.5 foot-pounds). That ain’t much. It doesn’t need to be much since these bolts aren’t in a compression application. They are loaded in shear, and as long as these bolts are snugged down to the proper torque, that’s sufficient.
Sign off your work
The good news is that owners can legally do a lot of work on their airplanes. However, as mentioned, there are catches. Catch No. 1 is that you must own or have access to the manuals. Catch No. 2 is that you must enter the work you performed in the aircraft records in a manner that’s acceptable to the Administrator. That’s FAA talk for the head of the agency.
The requirements for these entries are listed in FAR 43.9. It says if you perform PM, you shall make an entry in the maintenance records containing the following information:
1. A description of the work performed.
2. The date the work was completed.
3. The name of the person performing the work.
4. If the work was performed satisfactorily, the name certificate, certificate number and signature of the person performing the work. The signature constitutes an approval for return to service only for the work performed.
(This is a summary of FAR 43.9. Please refer to Resources for a link to the complete text. —Ed.)
Notice that the regulations do not require the entry to include the aircraft total time or tach time, but it’s extremely helpful to include that information.
An example1 of an entry for the work described above would read:
Month/day/year. “Greased left and right main landing gear wheels in accordance with information in the Cessna (model number) service manual and the Cleveland Wheel and Brake Component Maintenance Manual, Appendix A, paragraph A3.”
Signed: Joe Pilot Cert # 1245654
The point of this article is to make sure owners understand the freedom and the limitations that are part of owner-performed PM. Go ahead and do it, but make sure you do it right; by the book.
1For more about complete and detailed logbook entries, see “Deciphering Logbooks” by Kristin Winter in the November 2017 issue.
Know your FAR/AIM and check with your mechanic before starting any work.
Steve Ells has been an A&P/IA for 44 years and is a commercial pilot with instrument and multi-engine ratings. Ells also loves utility and bush-style airplanes and operations. He’s a former tech rep and editor for Cessna Pilots Association and served as associate editor for AOPA Pilot until 2008. Ells is the owner of Ells Aviation (EllsAviation.com) and lives in Templeton, California, with his wife Audrey. Send questions and comments to .
Part 43.3, Part 43.9, Part 43.13, Appendix A to Part 43
Identifying squawks and properly sequencing your Cessna refurbishment projects can save you time, money and aggravation.
So you’re now the proud, new owner of a not-so-new airplane that you plan to own for a long time. Fortunately, you properly vetted this new-to-you airplane during a thorough pre-purchase inspection, and you’re looking forward to renovating it into your ideal machine. The most important component in successfully making your dream a reality is to develop a cost-efficient, thorough and well-planned renovation.
A very important first step is to get to know the airplane before moving forward with major renovations and upgrades. I highly recommend that an owner fly their newly acquired airplane for at least a year and get it through its first annual inspection.
Even though a thorough pre-purchase inspection was done, be prepared for that first annual to possibly cost 10 percent of what you paid for the airplane. I’ve made this statement several times in the past during seminar presentations. Looking out at the audience, it’s interesting to observe the various reactions this comment generates in the expressions of those seated in front of me. Surprised or shocked looks indicate non-owners considering their first purchase. Nods of agreement come from seasoned airplane owners.
Why such an expensive first annual? Good question. It’s only natural for an owner who is planning to upgrade to a different airplane in the foreseeable future to defer maintenance issues that can be safely put off, passing the expense on to the next owner.
As you fly the airplane for that first year, it’s a good idea to keep a notebook with you. While comfortably cruising along, make detailed notes about things you would like to change to improve your experience in the airplane, as well as maintenance issues that may only be apparent in flight.
Note such items as cabin and instrument lighting, storage, passenger restraint issues, potential heating and ventilation improvements, seating comfort, instrument panel layout, etc. Over a year or so, you will be surprised to realize the number of details that you will want to include in your wish list that you weren’t at all aware of when you purchased the airplane.
I also think it’s a good idea to keep a small camera in the airplane and use it to capture images of paint jobs or interiors that you see and like; this can help you make better choices later. Designing a custom interior or paint job involves a lot of thought and planning. Having images of what you like will help the professionals you partner with to design and execute a project that will meet or exceed your expectations with no details overlooked.
The following is a list of sequenced projects that will lead to a thorough and high-quality renovation. We will cover all of these topics in greater detail in future articles to help you and your inspector find issues that could have been missed in earlier inspections.
– Overhaul or upgrade
– More horsepower, turbocharger conversion
– Converting carbureted to fuel-injected
• Improved baffles
• Alternator and starter upgrades
• Cowling modifications
• Replace old hoses
• Shoulder harnesses and belts
– Four-point vs. three-point
– Inertia-reel vs. fixed harness
– Airbag belts
– Adding harnesses to center and aft seats
• Fire extinguisher
• Ballistic parachute
– LED beacons, nav and landing lights
• Modern flameproofed interior materials
• De-icing systems
• Backup instrument systems
• How much digital automation is right for me?
• Keeping some existing analog equipment?
• What brand of equipment is the best investment?
• Instrument panel options
– Dealing with plastic panel overlays
– Converting to all-metal panels
– Panel lighting options
– Old circuit breakers and switches
– Autopilot options
– Onboard weather detection
• Gap seals
• Fixed and retractable landing gear
• Clean-up mods
• Auxiliary fuel systems
• Windshield conversions
– One-piece vs. two-piece
• Thicker windows vs. standard thickness
• Tint options
• UV-reflective glass vs. standard
• Windows with opening vents
• Stripping vs. topcoat over existing paint
• Stripping options
– Alkaline vs. acid-based strippers
– Media blasting
– Ice crystal blasting
• Getting the right design
– Design it yourself
– Use a professional
• Finishing products best for aluminum airplanes
• Best finishes for fabric-covered airplanes
• Aging airplane issues
– Leaking windows
– Corroded structural components
– Glue-covered and corroded inner cabin skins
• Approved seat modifications
– Taller seat backs
– Adding headrests to older seats
– Installing late-model seats in older airplanes
• Side panel and armrest design
– Factory configuration
– Modified or upgraded
• Storage options
• Insulation options
• Ventilation upgrades
• Lighting upgrades
– All-leather seats and side panels
– Fabric and vinyl seats and side panels
– All-vinyl seats and side panels
– Flame-proofed materials and Federal regulations
• How much interior installation can an owner legally do?
– Using kits
– Partnering with a local upholstery shop
• Typical warranty coverages for various projects
This list is not all-inclusive or cast in stone, but these various projects are loosely sequenced based on issues that could compromise previously completed work. For instance, old fuel cells that require replacement every 15 to 20 years should definitely be taken care of before a new paint job is done. The same is true for most window installations. If either of these two items are showing signs of aging and are likely to fail before that paint is in need of being done again, do the glass or fuel cells first.
All of this probably sounds complicated, expensive and time-consuming, and it is. Most owners stage these projects when it’s most convenient in their schedules or when they’ve recovered from the expense and downtime of the previous project. Additionally, many of these tasks can be partially or fully completed by an owner, saving money and giving one a real sense of accomplishment. In subsequent articles, I will describe some tricks we’ve discovered over the years that will help the do-it-yourselfers.
These kinds of restoration ventures don’t happen overnight. Air Mod was involved in completing five AOPA sweepstakes airplanes between 1994 and 2013. The time it took to complete most of these spinner-to-tailcone total renovations was close to a year, and they were not undertaken by only one shop. The “Better Than New 172” project in 1994 was a bit of a timing exception. The investment of long work days and seven-day work weeks resulted in an interior renovation that took about five months to complete, as opposed to the more common 10 to 12 months.
Be prepared to face the realities of the time it takes to transform your airplane into your dream machine. Until next time, fly safe!
Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded AirMod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .