172 Year Model Changes

This article is intended as an overview of the common Cessna 172 year model changes. It is NOT a substitute for the POH/AFM, STCs, or FAA approved documents applicable to your aircraft. 

Much of this is simply what I have observed from my time with the venerable 172.

I wanted to talk about some of the Cessna 172 model changes over the years. Some of these changes you may only find yourself using at trivia night while others are important operational changes that the pilot should be aware of and certainly alert to if the airplane is used for a checkride. I will do my best to point out these differences. I am going to focus on Lycoming powered 172s only, which started production in 1968. Of course, the 172 started production in 1956 however the early airplanes were powered by the six cylinder Continental O-300. I hope to cover these early Continental powered 172s at a later date. As always, your school’s procedures, Aircraft POH, and the FAA type certificate data sheet for your aircraft are always the relevant documents for operating your airplane. All of the following is UNVERIFIED and may vary slightly by year and serial. Always consult the POH for the exact aircraft you are flying for the most accurate information. Also note, while we largely discuss changes year to year, some of these changes were made mid year production and so may vary slightly. Refer to the revision date in your POH. 

Let's start with the 1968 172I. The India model was big for Cessna because it was the first year that they introduced the Lycoming O-320 engine. From 1968 until 1976 the 172 is powered by the O-320-E2D blue streak engine. This Lycoming put out 150 hp at 2700 RPM and had a TBO of 2000 hours. This was up from the 145 hp Continental that had an 1800 hour TBO. It's very easy to spot a continental versus a Lycoming powered 172 by looking at the exhaust pipes. A Lycoming powered airplane has one exhaust pipe coming out the right side of the cowling at a slight angle while the continental powered 172s have two exhaust pipes coming out straight down. Aftermarket STCs are available to this engine boosting it to 160hp. If the airplane has been modified, the STC paperwork must be onboard the aircraft with the POH and will explain to use the original performance charts as performance change is negligible. Other STCs upgrade the engine to an O-360, 180hp. This STC comes with supplemental performance charts and also must be kept in the aircraft. From 1968 until 1976 Cessnas had a fuel capacity of 42 gallons total 38 usable. In 1969, the kilo model was introduced. This airplane had an optional Long range fuel tank which carried 52 gallons total and 48 usable. A piece of trivia here… Cessna moved from the India model straight to the kilo model skipping the Juliet model. While the Juliet model was being developed, Cessna designed a new laminar flow cantilever wing, that's a strut-less wing. They also incorporated a full flying tail or stablelater. As the Juliet program developed, Cessna realized there were simply too many changes to this year model and re-designated the program the Cessna 177 Cardinal, hence the first Cardinal being produced in 1968. So Cessna skipped from the India straight to the kilo model in 1969. 

1969 kilo is easy to identify because of the redesigned rear window. They went from the slightly tapered window to a more rectangular window. 1970 there was minimal change except to the wing tips as they introduced the slight wing tip droop, still standard today. 1971 was the introduction of the Lima model at which time they moved the landing light from the left wing leading edge to the front of the cowling directly below the spinner. The landing light remained there until 1982 at which point they moved it back into the left wing leading edge due to reports from operators of reduced bulb lifespan due to the engine heat. To this day, production still remains with the landing light in the left wing leading edge. Also in 1971 Cessna changed the design of the landing gear from a spring steel type to a tubular landing gear. The tubular landing gear is easily identifiable by the metal speed fairing covering it. 1972 saw minimal changes to the lima model which brings us to 1973 and the introduction of the Mike model. This was a significant year for Cessna as they introduced the camber cuff wing to their single engine series. The new wings had a slight droop added to the leading edge profile. This slight droop allowed the wing to produce lift at a slower speed, lowered the stall speed and improved slow speed handling characteristics. There are several aftermarket STC's offered that essentially add the camber cuff to the wing. These STOL kits are an extended leading edge that is riveted over the original leading edge. They claim the camber cuff wing introduced in 1973 does not affect the top end speed of the airplane. 1974 and 1975 Mike models had minimal changes to them.

In 1976 Cessna made a fairly substantial change from the pilot’s viewpoint as they switched from the airspeed indicator indicating in miles per hour to knots. There was also an effort made to redesign the pilot operating handbook into a more streamlined flow. Prior to this, the manuals contained minimal information and were more like an information guide. The 1976 revision included significantly more information which was useful to the average student pilot when learning how to fly. The format still remains today. Also in 1976 the engine instrument cluster was moved from the right side of the panel to the left side of the panel directly above the master switch. 

That brings us to 1977 and the introduction of the November model. There quite a few changes with the November model. The biggest was the introduction of a new engine; the O-320H2AD. This four-cylinder Lycoming put out an extra 10 hp for a total of 160 hp. The H2AD motor is the only Lycoming used in a 172 that has a 6 quart capacity. All of the other Lycoming engines have an 8 quart capacity. It's easy to visually identify an H2AD 172 by looking at the location of the oil dipstick door. All Lycoming powered 172s have the dipstick access on the right side of the cowling, however, the H2AD powered 172s have oil dipstick access directly in the center top of the cowling. The H2AD motor was only used on the November model from 1977 until 1980. This engine was plagued with multiple reliability issues which led Cessna to change in 1981 to the O320 D2J, also a 160 hp engine. Many November model 172s have been modified with a D2J engine. This is easy to see if you ever come across an airplane that has an oil door in the top center of the cowling that has been riveted shut and a new one cut in the more traditional area on the right side of the cowling. 1977 also saw the introduction of the modern style flap selector which is still used today. This selector and indicator allowed the pilot to pre-select the flap position. Also of note with the introduction of the November model the fuel capacity went up to 43 total 40 usable with optional long range thanks 54 total and 50 usable. This remained the fuel capacity for all November and Papa model 172s. Lastly, with the introduction of the November model in 1977, full oil was now included in the “Basic Empty Weight” of the aircraft in the weight and balance section. Prior years, oil was not included in the basic empty weight, previously called “Licensed Empty Weight” and had to be added on the weight and balance calculation. The 1978 November model changed from a 12V electrical system to a 24V electrical system. The flap speed for flaps 10 or also changed. 

***Let me get into a discussion about flap speeds and flap settings for different types of takeoffs. I will be referencing all of the year models for this discussion. From the beginning of 172 production until the end of the November production in 1980, 172s came with 40 degrees flaps. In order to get the gross weight increased from 2300 to 2400 lbs on the Papa, flaps were limited to 30 for go around climb performance considerations. So Papa and later airplanes have 30 degrees flaps. Prior to 1976, when the airspeed indicator read in miles per hour, the top of the white arc was 100 mph; that was Vfe. At and below 100MPH, all 40 degrees could be extended. When the airspeed indicator was changed to knots in 1976, the maximum flap extension speed was placarded at 85knots, top of the white arc, at which all 40 degrees could be extended. In 1978 the maximum speed for flaps 10 was increased to 110 knots while the rest of the flaps remained at 85 knots. This is true of airplanes still in production today. Half way through the production year in 1979, the POH was revised. The POHs dated July 1, 1979 and later introduced a new short field takeoff procedure. Normal takeoffs prior to July 1979 should be accomplished with wing flaps up and short field takeoffs should also be accomplished with wing flaps up. Obstacles should be cleared at Vx. This is quite clearly displayed in the pilot operating handbook, section 4. After July 1979, the normal takeoff was changed to flaps UP or 10 and Short field takeoff to flaps 10, and this remains today. With this procedure, an obstacle clearance speed should be used to 50 feet instead of Vx. This is explained in the amplified procedures of section 4. All soft field takeoffs in any 172 should be accomplished using flaps 10. So again, the big take away is that in July 1979, the short field takeoff flap setting was changed from flaps UP to flaps 10. Also in July 1979 the normal takeoff was changed from flaps UP to flaps UP or 10. So it would be acceptable in these later aircraft to perform a normal takeoff at flaps 10, although I rarely see it done. Be familiar with this section of your POH on the day of your checkride and if any questions arise, hopefully prior to the flight, be sure to point out what your airplane calls for on a short field takeoff. You should be referencing three areas of section 4; Speeds for normal operation, Checklist Procedures, and Amplified Procedures. One final note about flaps, the go-around flap setting, which Cessna calls a balked landing, is always flaps 20, regardless of if the airplane is equipped with 30 or 40 degrees of flaps. Flaps 20 should be selected immediately after go around power (full throttle) to reduce the drag of full flaps but keep the increased lift that flaps produce. ***

In 1981 the papa model is introduced with the new O-320 D2J engine, also 160 hp. In an effort to increase the gross weight to 2400 pounds Cessna had to limit maximum flap extension to flaps 30 for go around climb performance. The papa model also came with optional extra long range tanks, called integral tanks, which held 66 gallons total, 62 usable. For the remainder of the Papa model production years there were minimal changes with the exception in 1982 the landing light was moved from the cowling to the leading edge of the left wing as previously mentioned. 

From 1986 to 1996 Cessna did not produce 172s due to product liability lawsuits. When production resumed it did so with the introduction of the Romeo model. You may hear any post 1996 airplane referred to as a “restart” airplane as this is when Cessna restarted production of the 172 line. All restart airplanes were internally primed for corrosion protection from the factory. This is easy to see by pulling an inspection panel and noticing the green primer instead of bare metal. Big changes with the Romeo model were the introduction of the fuel injected Lycoming IO-360L2A. This engine stock from Lycoming is rated at 180 hp at 2700 RPM. However, Cessna chose to de-rate the engine to 160 hp by limiting the RPM to 2400 RPM. The gross weight of the Romeo model is 2450 pounds. In 1998 Cessna introduced to the S model. The S model again had a gross weight increase to 2550 and it was at this point that they did out with the derate and allowed the full engine rpm of 2700 therefore increasing the horsepower to 180. They did this by using a different pitch propeller on the airplane. Many Rs have been converted to Ss through Cessna modification kit MK 172–7 2–01. 172S models have remained the same throughout the years with the exception of the introduction of the G1000 which occurred in 2005. Therefore, the only restart 172’s that are steam gauge powered were produced from 1996 to 2005. All restarts carry 56 gallons total, 53 useable. 

Have more and/or better info? Please share it with me and I’ll update the article.