Reims Aviation & the French Cessnas

Reims Aviation & the French Cessnas


A History of Cessna Aircraft’s Partnership in France.

The French city of Reims is best known to aviation historians for the Grande Semaine d’ Aviation de la Champagne, the first international airshow, held in August 1909. The Grande Semaine rivaled today’s EAA AirVenture Oshkosh, with some 500,000 visitors over the course of a week. The Grande Semaine featured air races and exhibition flights, and was considered by many to be a coming-out party for the commercial viability of heavier-than-air aviation.

Fifty years later, Reims was the site for another meeting of international aviation minds; this one would shape European General Aviation for several decades to come. 

Looking for opportunity

General Aviation was booming in the United States in the late 1950s. Cessna Aircraft Co. had emerged as a leader in the light aircraft market, riding the success of the Cessna 140 and 170 series into the even more popular Cessna 172. 

Cessna was looking to broaden its distribution outside the United States, and saw opportunity in the quickly-growing European General Aviation market. Cessna had established a dealer network abroad, but transportation costs and high tariffs made it difficult for Cessna to bring price-competitive products to Europe. 

Executives began the search for a European partner which could manufacture Cessna products under license. The ideal partner would have spare production capacity and a trained workforce to facilitate a rapid spool-up of production of Cessna-licensed aircraft. 

French aircraft manufacturer Societe Nouvelle des Avions Max Holste was founded in 1933 by engineer Max Holste. Avions Max Holste had produced several airplanes (both of their own design and on license) in the postwar years. However, it had not found a large market for its flagship Broussard series of turboprop transports and by the end of the 1950s, the company was facing financial trouble.

France was Europe’s most active country for General Aviation at the time, with more than 3,000 aircraft in the air. A partnership with Avions Max Holste made good sense for both sides. Cessna would gain access to a skilled workforce and manufacturing facilities in the heart of France; Avions Max Holste could delicately extract itself from its financial woes by spinning off its turboprop line to Nord Aviation, and focus on producing commercially-proven Cessna aircraft.

Negotiations were brief, spanning only a few meetings. A partnership agreement was signed February 16, 1960. The agreement was approved by the French government in May of the same year. Cessna would own a 49 percent share of a new company, Reims Aviation, with the shareholders of Avions Max Holste retaining the balance of ownership. At the time of the agreement, Reims had 280 employees. The name change became official in January 1962.

Reims Aviation was granted the sole franchise to produce Cessna products in Europe. Cessna promised Reims Aviation access to their existing Cessna International dealer network. 

To start, Reims would produce the Cessna 172 and 175. Other models would follow after the completion of the initial production run, which was slated to begin in 1963 with full production by 1964. 

The first models

Production started on time. The first Reims Cessna aircraft was completed in April 1963 and rolled off the line bearing serial number F1720001, with the F-prefix denoting an aircraft assembled in France. This “F” nomenclature carried through to the model number—the 172Ds produced by Reims would be the Reims Aviation F172D. 

The F172D was essentially a kit version of the Cessna 172D. All airframe parts were manufactured by Cessna in the United States and shipped to Reims for final assembly and paint. The engine was a 145 hp Continental O-300-D produced by Rolls-Royce in England. With the exception of their data plates and flight paperwork, the first 18 Reims F172Ds were identical to their U.S. counterparts.


The F172 was a hit, and production ramped up quickly. By the end of 1964, Reims Aviation had produced 100 F172s, and a dozen aircraft a month were leaving the small Reims factory.

At the same time, Cessna attempted to import the rebadged Cessna 175, known as the “Powermatic” P172D. The Powermatic featured a 175 hp Rolls-Royce Continental GO-300-E engine with a geared reduction drive and constant-speed propeller. The P172D was pulled from Cessna’s U.S. lineup in 1963; and only three FP172Ds left the Reims factory. 

Another P172D airframe was received by Reims and converted into a prototype for a military liaison light aircraft; powered by a Continental IO-360. This prototype, bearing the model designation FP172M, provided a proof-of-concept for the Cessna T-41B training aircraft, later produced in the United States for the U.S. Army. The FP172M project was abandoned.

The transition from kit assembler to manufacturer was rapid. Reims Aviation began to manufacture subassemblies in early 1964. Nearly all components for the F172 were being made in France by 1965. The Rolls-Royce Continental engine and spring steel landing gear were the only imported parts in 1965’s F172E models.

Though Reims was bound by agreement to make their aircraft parts-compatible with U.S.-manufactured Cessnas, Reims made small improvements in their assembly process. Most importantly, all aircraft leaving the Reims factory after mid-1964 were corrosion-proofed. 

Full production

Reims Aviation reached full production capacity in 1965. The F172’s price point (approximately $10,000) appealed to flight clubs and private owners. A French government program helped to boost sales—the program subsidized up to 50 percent of a French-built aircraft’s cost when purchased for flying club use. At the end of 1965, Reims was producing 15 F172s per month.

Even with brisk sales of the F172, Reims and Cessna saw additional opportunity in Europe. European customers clamored for a two-seat trainer: the Cessna 150. The model was extremely popular among U.S. customers. Cessna produced some 3,000 Cessna 150s in the United States in 1966 alone. However, tariffs and transportation costs made the F172 a cheaper option than an imported U.S.-made Cessna 150.

Plans were made to bring the Cessna 150 to Europe. Production of the F150 began in February 1967. In the first year of production, Reims Aviation produced 67 F150F aircraft.

Reims Aviation needed more space to meet the increased production demand, and broke ground in April 1967 on a 150,000 square foot factory at Reims-Prunay Aerodrome (LFQA). By June 1968, Reims had transitioned all production to the new facility, which soon expanded to over 200,000 square feet.

Cessna’s European dealer network had also grown to help distribute Reims and Cessna aircraft. Based in Brussels, Belgium, Cessna Europe had 38 dealers in 24 countries, including a distributor behind the Iron Curtain in Czechoslovakia. 

Reims Aviation’s CEO, former French fighter ace Pierre Clostermann, bragged in a 1968 Flying interview that Reims would soon be supplying Cessna’s European dealer network with most of its single-engine aircraft. He predicted Reims’ production would hit 1,000 aircraft a year by 1975. These bold estimates were based in part on a new product positioned to expand Reims’ portfolio beyond the F150 and F172. 

The FP172M concept, the 210 hp IO-360-powered prototype which had been mothballed in 1963, re-emerged at the 1967 Paris Airshow as Reims’ new flagship product: the Reims Rocket Model FR172E. This new high performance 172 would be produced exclusively for civilian sale in Europe by Reims Aviation. The Rocket was positioned to fill the niche between the F172 and the imported Cessna 182 Skylane. In this respect, it was similar to the fixed-gear Cessna 177 Cardinal, which was not produced in Europe. 


The FR172E Reims Rocket’s 210 hp Rolls-Royce Continental IO-360-D fuel-injected engine and constant-speed propeller produced a maximum of 2,800 rpm at takeoff and gave the aircraft a 125-knot cruise speed. The aircraft was at least 20 knots faster than comparable F172s, with only slightly increased fuel consumption and maintenance costs. 

The Rocket’s name was as much for its sound as its speed. An article in Flying described the Rocket as producing “a helluva racket—about 84 dB at 1,000 feet.” The Rocket also boasted a 2,500-pound gross weight (an increase of 200 pounds from the standard F172) and a useful load of approximately 1,000 pounds. The aircraft was in many respects superior to the early 177 Cardinals, and close in performance and payload to the Cessna 182. The Reims Rocket was produced through 1977. Reims built almost 600 Rockets in the ten-year production run.

Military customers also expressed interest in the Rocket. Reims produced eight specially-equipped FR172E aircraft in 1969 for the Irish Air Corps. These aircraft saw active duty fighting in Northern Ireland. 

Cessna’s eight-seat twin-engine Model 411 made a brief appearance at the Reims factory in 1967 and 1968. Eight aircraft were assembled from kit form and delivered as the Reims Cessna F411. 

As the 1960s came to a close, 400 employees of Reims Aviation were producing approximately 300 aircraft a year. The first five years (1965–1969) of full production at Reims were an overwhelming success. A total of 1,331 aircraft rolled off the line, compared with the production plan’s goal of 1,017. About two-thirds were F172s. The remainder was split between the F150 and the new FR172E.


The 1970s saw the continuation of F150, F172 and FR172E production, and the adoption of several other popular Cessna models.

Cessna’s 150 Aerobat was the next model to cross the Atlantic. The A150K Aerobat was produced by Reims Aviation starting in late 1969 as the FA150K. These FA150K Aerobats were powered by the same Rolls-Royce Continental O-200-A engine as the standard F150 models. A total of 120 FA150K and FA150L models were produced.

The Aerobat soon received a Reims customization and was upgraded with a Rolls-Royce Continental O-240-A engine producing 130 hp. This Aerobat, known as the FRA150L, has a high power-to-weight ratio and members of online European aviation forums often call it a joy to fly. Both L and M models were produced in fair numbers, for a total of 272 FRA150L and FRA150M models.


From 1968 to 1971, the Reims F172s differed somewhat from their U.S. counterparts. Cessna changed the 172’s powerplant to the four-cylinder 150 hp Lycoming O-320-E2D starting with 1968’s Cessna 172I model; Reims did not adopt the new engine until 1972’s F172L.

1974 marked the peak of Reims Aviation’s production. Reims’ 515 employees produced 474 aircraft at the 260,500-square-foot Prunay Aerodrome factory. The F172 was the most common aircraft, with a production rate of 150 aircraft per year at the end of 1974, followed by 105 F150s, 31 FR172s and 20 FRA-150s. 

While the fixed-gear Cardinal was not produced by Reims, the 177RG Cardinal RG retractable made a brief appearance in France. A total of 177 FR177RG aircraft were produced from 1972 to 1978. 

The Cessna 182 was not licensed to Reims in its early years, perhaps due to the success of the Reims Rocket. This changed in 1975, when Cessna granted Reims the license to produce the 182P Skylane and R182 Skylane RG. 25 F182P models, 145 F182Q models and 67 FR182 models were manufactured by Reims between 1976 and 1984.


The F150 was replaced by the F152 in 1978 and mirrored the Cessna 152s sold in the United States. Reims also produced a 152 Aerobat, the FA152. Reims manufactured 622 F152 and FA152s between 1978 and 1985.

The Reims Rocket was supplanted by the Hawk XP in 1977. The Hawk XP, also known as the FR172K, featured the same airframe and powerplant combination as the Reims Rocket, though the Rolls-Royce Continental IO-360-K engine was derated to 195 hp and 2,600 rpm on takeoff. This adjustment complied with new European noise regulations. The new aircraft was nearly identical to the U.S. model Hawk XP. Reims produced 85 Hawk XPs between 1977 and 1981.

The Cessna 337 Super Skymaster was licensed to Reims Aviation in 1969, with the first delivery in 1972. Reims produced almost 200 Super Skymasters between 1972 and 1980, divided nearly equally between pressurized and nonpressurized versions.


Approximately 60 of the pressurized Super Skymasters were equipped with special STOL modifications and provisions for carrying military ordinance. 21 of these FTB337G model Skymasters were sold to the Rhodesian Air Force. In 1980, Cessna gave full Super Skymaster production rights to Reims. However, Reims did not produce any Super Skymasters after 1980.

Reims Aviation employed 540 people at the end of 1979 and produced 373 aircraft that year.


As with many major aircraft manufacturers, Reims was hit hard by the downturn in General Aviation which started in the late 1970s. 

Production slowed to a trickle by 1983. Though Reims Aviation had 531 employees at the end of the year, only 92 aircraft left the factory. By 1986, Reims Aviation, like Cessna, was no longer producing piston singles. Reims directed its attention to the production of a new aircraft. 

The Reims F406 Caravan II, a twin-turboprop derivative of the Cessna 404, debuted at the Paris Air Show in May 1983. The Caravan II could carry up to 12 passengers at just over 250 knots, with a range of 1,030 nm. Cessna produced most of the parts in the United States and final airframe assembly took place at Reims Aviation’s Prunay factory. The first aircraft was delivered in April 1985.

By 1989, Reims Aviation was only producing one model of aircraft, the F406 Caravan II, at a rate of one per month. 


In May 1989, Cessna chose to divest from its interest in Reims Aviation; selling its shares to Compagnie Francaise Chaufour Investissement (CFCI) of Paris. As part of the sale, Cessna agreed to offer CFCI the right of first refusal to produce Cessna products in Europe if Cessna were to ever restart piston-powered aircraft production. 


The employees of Reims Aviation continued to work throughout the early 1990s, though much of their efforts were concentrated on producing parts for other manufacturers’ aircraft, including Dassault, Airbus and ATR. Reims saw a brief renaissance, reporting over 500 employees in 1991.

In 1991, Cessna considered relaunching the Model 425 Conquest I and contracting with Reims Aviation for production. Ultimately, this project fell through. A few years later, Reims’ maintenance department began to remanufacture used Reims Cessna light aircraft (primarily F172s), offering complete refurbishment for a fraction of the price of a new aircraft.

Cessna declared in 1994 that its single-engine restart program would not include a production license for Reims Aviation. In December 1995, Cessna reversed course, announcing that Reims would produce 200 airplanes a year for European and African markets. A follow-up announcement in 1997 indicated that Reims would also start to remanufacture Reims Cessna F150 and F152 airframes for use in flying clubs and flight schools. 

A trial production run was conducted in 1997 and three Cessna 172R Skyhawk kits were shipped to Reims Aviation. By September, Reims had booked 22 orders for new 172s and 182s. 

However, the CFCI investment group decided against restarting Cessna production and chose to focus on producing the F406 Caravan II and subcontracting for other manufacturers. The three 172R aircraft were returned unsold to Cessna. 

Caravan II production continued, and 80 aircraft were delivered to customers between 1985 and 1997. Most were configured for transport use, though customs and border protection agencies of several nations ordered surveillance versions. 


In 2003, Reims Aviation declared bankruptcy. The bankruptcy court split the company into Reims Aerospace, which would focus on subcontracting; and Reims Aviation Industries, which would produce the F406 Caravan II. 

The Type Certificates for most of the Reims-produced Cessna aircraft were transferred to Cessna in 2006. This allowed owners of Reims Cessnas to register their aircraft on the U.S. N-number registry with minimal difficulty. In the eyes of the FAA, Reims Cessnas are “considered domestic products for the purpose of design certification and continued airworthiness” per Type Certificate A4EU.

Reims Aviation Industries continued production of the F406 Caravan II until 2013 when the company went into receivership, leaving its 70 employees out of work. 

In March 2014, the remains of Reims Aviation Industries were sold. The Type Certificate and production rights to the F406 were transferred to ASI Innovation. Continental Motors has since partnered with ASI Innovation with the intent to restart production of the F406, but to date, no aircraft have been built.

Reims Aerospace was bought and renamed in 2011 by Austrian investors to Novae Aerospace Industry. This company continues to operate in the former Reims Aviation facility at Reims-Prunay Aerodrome, producing parts for Airbus, Dassault and others.

Vive le avion!

Reims Aviation’s partnership with Cessna followed the same arc as Cessna’s business in the United States. 1965 to 1975 were the golden years at Reims Aviation, followed by gradually waning demand in the mid-1980s. By 1986, both Reims and Cessna had abandoned light piston singles; choosing instead to focus on multi-engine aircraft.

Over the course of its 23-year run of producing Cessna singles, Reims Aviation helped bolster the growth of European General Aviation by bringing affordable aircraft to the European market en masse. 

Reims Aviation built more than 6,300 aircraft, including 12 different Cessna single-engine models and four twins. Reims Aviation no longer exists, but thousands of Reims aircraft continue to ply the skies over Europe and around the world.

Scott Kinney is a self-described aviation geek (#avgeek), private pilot and instructor (CFI-Sport, AGI). He is a technical editor for Cessna Flyer. Scott and his partner Julia are based in Eugene, Oregon. They are often found buzzing around the West in their vintage airplane. Send questions or comments to .

Sources Online:
Marais, Frédéric. “Novae Aerospace Industry, ou le spectaculaire redressement d’un avionneur historique de Reims.” Traces Ecrities News, May 9, 2017.

“GECI Aviation, an organisation making a place for itself on the world twin turboprop aircraft market.” GECI Aviation. April 5, 2010.

“Divestiture of Reims Aviation Industries and bankruptcy of GECI Aviation.” GECI Aviation. April 28, 2014.

Pope, Steven. “Continental To Build Former Cessna Cabin Class Twin.” Flying, March 27, 2014.

Flying. Apr. 1965, Jan. 1966, Sep. 1967, Apr. 1968, Jun. 1969, Jun. 1970, Jun 1977, Oct. 1979, Sep. 1980, Aug. 1983, May 1989, Jul. 1989, Dec. 1991, May 1993, Dec. 1994, Jan. 1996, Mar. 1997, Sep. 1997. [Note: many back issues of Flying, including all cited above, are available free on Google Books,]

FAA listing of Reims Cessna
TCDS documents (past and current):


Jane’s All the World’s Aircraft. New York, NY: McGraw-Hill, 1967, 1968, 1971, 1972, 1976, 1980, 1985, 1988, 1996, 1999.

Murphy, Daryl. The Planes of Wichita: The People and the Aircraft of the Air Capital. Bloomington, IN: iUniverse, 2008.

Schoenberg, Eyvinn Hansen. Plane Talk: Cessna Export Tales. Philadelphia, PA: Xlibris, 2003.

Simpson, R.W. Airlife’s General Aviation: A Guide to Postwar General Aviation Manufacturers and Their Aircraft. Shrewsbury (UK): Airlife Publishing, 2000.

Simpson, Rod. The General Aviation Handbook. Hinckley, MN: Midland, 2005. 

Smith, Ron. Cessna 172: A Pocket History. Stroud (UK): Amberley, 2010.

Shiel, Walt, Jan Forsgren, and Michael R. Little. T-41 Mescalero: The Military Cessna 172. Lake Linden, MI: Slipdown Mountain Publications, 2006.


The High & the Writey: Never Kick a Frozen Chock


Field-tested rules about what to do, and what not to do.

I officially entered Old Pilot status a few years ago and with that designation comes a responsibility to preach to you, the choir. 

You could—and up until now, you have—gotten along fine without my advice and bloviating about all things aviation. Let’s assume though that even though your flying life has been going along OK without my unsolicited guidance, the bon mots that I am about to “mote” you with will be the cream cheese icing on your aeronautical carrot cake.

Please relax. There will be no test after I list my rules. There isn’t even a requirement that you follow any of them. Many of them might seem insipid and not very well-thought-out. 

Rest assured that each one has been tested, in the field, by yours truly. These rules are the result of multiple times I have been scared, cold, hot, nauseated, or just plain marinating in a Crock-Pot of stupidity.

Much like the Federal Aviation Regulations, most of these guidelines tell you what you should not do, rather than what you should. The first set of rules are ones that I learned in my callow youth as a lineboy, ramp rat and semi-employed CFI and charter pilot. Following those will be rules that will interest you if you fly or ever wanted to fly airplanes for a living. 

Things I learned as a lineboy/CFI

• Never kick a chock. When I was a lineboy I mastered the skill of kicking a chock across a hangar floor with it ending up against an aircraft’s wheel. It was later that I learned that chocks can freeze solid to the ground in cold weather and be full of angry wood bees in warm climes.

• Another hard-learned lineboy rule: Never walk through a totally dark hangar. Rotor blades from helicopters, wings of airplanes and random aircraft antennae will seek you out, smack you in the head and knock you down as you pick your way back to the hangar door.

• Never prop a stranger’s airplane. I know this rule seems harsh, but I have propped hundreds of airplanes over the years and have kept all 10 of my fingers by only helping pilots I know and trust.

• If you can’t stand up and/or keep falling on the ramp, it is probably too icy to taxi your airplane on it.

• Always check your own fuel caps, oil caps and access doors.

• There is always time for a clearing turn.

• You should never hurry. If you are on the ground and get confused, set the parking brake and take some time to figure it out. If you are in the air, ask for holding or delaying vectors. Never fly on ATC’s schedule. They are never at the crash scene. You always arrive first.

• Never let a dispatcher, FAA briefer, your boss, your student or an air traffic controller decide your fate. You are in command—so, command.

• If you are on the line crew and are changing jet fuel nozzles, always turn the truck off before you try to change over from over-the-wing to single point. (It took me a couple of Jet-A showers before I learned this one.)

• Never hold a garbage can up to a big airplane in an attempt to dump the toilets. This looks like a good idea at the time, but trust me, it isn’t pretty.

• There are usually two kinds of air hoses in an airplane maintenance shop. One is a low-pressure air hose and the other is a high-pressure nitrogen hose. One hose will fill up your air mattress and bicycle tires. The other, if not used properly, can blow your fingers off.

• Speaking of shop hazards, I have made it a personal rule that I never handle hydraulics or high-wattage electricity. Any time a mechanic says, “You can service that yourself; just stick your head in the wheel well, and…” I defer to the A&P and ask him or her to take care of it. I like my head—and a few dollars is a small price to pay for me to keep it attached to my neck.

• Never, ever be the first to volunteer for anything. Let another pilot try flying through that hole in the line of thunderstorms or attempt that 35-knot crosswind takeoff.

• You should never comment to other people flying with you on how well you just traversed that area of thunderstorms without much turbulence. Karma will rear up and kick you in the butt if you do, and you’ll immediately get a terrible ride. I have tested this rule a lot and it has worked every time.

• Always write down your last frequency somewhere. Nowadays most radios are flip-flop, but you should never have to search for a frequency longer than a minute or two, even if you must break out and look at a navigational chart to do so.

• Whatever facts about your flight that you don’t know—and you will not know a lot—can always be looked up.

• The best pilots are self-doubting pilots. Never trust a pilot who thinks he or she knows everything.

 And now, a few things I learned while flying in the airline world:

• You should realize that you never look as good at the layover motel’s swimming pool as you think you do.

• You can never be senior enough.

• If you ever do get senior enough, avoid trips that go through ATL or DFW.

• You should always take the time to admire the pictures that are shown to you by flight attendants of their cats, girlfriends and boyfriends.

• Absolutely nobody wants to hear stories about your dog, your kids—or your political opinions.

• No matter how expensive, big and fancy an airplane you are flying, it will still feel like crap to you when you are flying at 3:00 a.m. I learned this one flying international on the Boeing 777.

• You will never get back the Christmas mornings you flew a trip instead of spending it with your spouse and kids. It is a cost of doing the job, and it hurts.

• The company you fly for is not a family, and it is certainly not your family.

• The most scared person on my flight crew almost always wins when it comes to deciding whether to take a course of action or to deviate around weather. Scared copilots have kept me from doing something stupid dozens of times in my career.

• You never know which flying trip will be your last, so enjoy them all as much as you can.

What are your unshakable flying rules? Send them to me in care of Cessna Flyer, and we’ll all get in the hangar and discuss them at the next Rules Committee meeting.

Kevin Garrison’s aviation career began at age 15 as a lineboy in Lakeland, Florida. He came up through General Aviation and retired as a 767 captain in 2006. Currently Garrison is a DC-9 simulator instructor and a 767 pilot instructor; his professional writing career has spanned three decades. He lives with the most patient woman on the planet on a horse farm in Kentucky. Send questions or comments to .

Hone in the Range: Lycoming Oil Pressure

Hone in the Range: Lycoming Oil Pressure

Engine oil provides lubrication and cooling for an aircraft’s engine. Ensuring your oil pressure remains “in the green” is one of the most important things you can do for your engine’s health and longevity. 


Oil pressure in an engine is like blood pressure in a human. Both are important indicators of internal health, and both should be kept within proper parameters to ensure longevity.

Operating pressure

The normal oil pressure range for most Lycoming engines is between 60 to 90 pounds per square inch (psi). This range is indicated by the green arc on the oil pressure gauge. The maximum oil pressure allowed for short durations is 115 psi on most models. The maximum allowable pressure has increased over the years from 100 to 115 psi. The top red line on most oil pressure gauges is 100 psi. The lowest allowable limit for oil pressure with the engine operating at idle with hot oil is 25 psi, which is indicated by the lower red line on most oil pressure gauges.

Lycoming generally sets the operating pressures for cruise rpm on their factory-rebuilt engines to between 75 to 85 psi. Most new, rebuilt or overhauled engines require a slight adjustment of the oil pressure to finalize the setting once the engine break-in process is complete. 


Oil flow through a typical Lycoming engine

Lycoming engines use a “wet sump” oil system. This simply means that the oil sump is mounted under the engine and oil flows by means of gravity back to the sump after it has been pumped through the engine. The sump is completely open on the top so that all areas of the engine can drain back into it, and it functions like a large drain pan. “Dry sump” systems have a separate dedicated oil tank. Oil is routed to the tank once it has completed its course through the engine. 

The Lycoming oil pump is located in the accessory housing. It consists of an aluminum outer body and two steel impellers, one of which is gear-driven off the crankshaft. (See photos 01 and 02, this page and photo 03, page 35.) It produces oil pressure in direct proportion to how fast the gears spin. At higher engine rpm, the pump produces more oil pressure than at low engine rpm. 

Oil is drawn up through the suction screen in the sump and through the oil pump impellers. The oil is then routed to the thermostatic bypass valve (also called a vernatherm valve). 

Oil continues to flow to the oil filter adapter on the accessory case and through the oil filter (or screen if the engine is not equipped with an oil filter). From the filter, oil is routed to the oil pressure relief valve. The oil pressure relief valve is located on the top right side of the crankcase. It relieves excessive oil pressure by opening a drain port to the sump to bypass some of the oil flow if oil pressure gets too high. 

Oil then travels to the crankshaft bearings and through predrilled passageways in the case to lubricate the internal engine parts through either pressure or splash lubrication. After completing its course, the oil drains back to the sump.


Thermostatic bypass valve

The thermostatic bypass valve is similar to a thermostat in an automotive engine cooling system. (See photo 04, page 35.) The valve remains open when the oil is below 180 F, allowing the oil to bypass the passage to the oil cooler. As the oil heats up past 180 F, the vernatherm expands and eventually contacts its seat, forcing oil to pass through the oil cooler.

An engine that has abnormally high oil temperature may have a thermostatic bypass valve that is not expanding as it should with increased temperature, or that is not seating properly due to a worn seat. The valve seat wears over time and typically gets a worn groove that gets slightly worse every time it closes. If the valve gets excessively worn it allows some oil to bypass the oil cooler even when the oil is hot. (See photo 05, page 35.) Some of the older bypass valves had retaining nuts that were improperly crimped during manufacture. Lycoming issued Mandatory Service Bulletin 518C that contained instructions for performing a heat treatment using a special Loctite to permanently secure the nuts in place. Valves that have had the Loctite treatment are typically inscribed with an “L” near the part number to indicate they have been repaired. 

As of August 2016, Lycoming no longer recommends this repair. Mandatory Service Bulletin 518D supersedes 518C and states that valve repair/rework is no longer allowed. Older-style valves with loose crimp nuts should be replaced.

Engines that suddenly develop an oil temperature problem may have one of the older-style valves with an improperly crimped nut that has come completely loose. Lycoming Service Instruction 1565 provides the procedure for replacement.


Oil pressure relief valve

The oil pump is a direct drive pump. This means that the pump impellers spin in direct relation to engine speed and produce oil pressure that also varies directly with engine speed. 

At high engine rpm, the pump produces far more pressure than the engine is designed to handle. Therefore, a pressure regulator must be incorporated into the system to keep pressures high enough at low engine speeds to protect the bearings and low enough at high engine speeds to prevent rupturing or damaging any of the engine components. 

The oil pressure relief valve (or oil pressure regulator) is located on the top right side of the crankcase; behind the number three or the number five cylinder, depending on whether it’s a four- or six-cylinder engine. (See photo 06, page 36.)

The oil pressure relief valve is very basic in its method of relieving excessive oil pressure. It consists of an aluminum housing with a strong spring, which presses against a steel ball. The spring keeps the ball seated. 

As oil pressure builds beyond the amount the spring is adjusted to maintain, the ball is forced off its seat by the excessive pressure. This exposes a passageway (bypass) that directs excess oil back to the sump, relieving some of the oil pressure. 

There are three types of housings. The latest style has an adjustable spring seat that can be cranked in or out as needed by means of an attached castellated nut on the end of the shaft. 

The older styles were adjusted by removing the housing and spring and adding or subtracting washers behind the spring to increase or decrease pressure. (See photos 07 and 08 on page 36 and photo 09 on page 38.)

The oldest style housing was short and had an adjustment of zero to three washers maximum. (See photo 10, page 38.) The longer housing allowed up to nine washers maximum to increase spring tension. (See photo 11, page 38.) Each added washer increases oil pressure approximately 5 psi. On the externally adjustable models, one turn in (clockwise) increases oil pressure approximately 5 psi. 

There are also springs of varying tensions and lengths which can be interchanged if the above adjustments do not yield the desired results. Some of the springs are color-coded to help differentiate them from one another. The most commonly used ones are the white LW-11713 springs (thick, heavy springs that are used to increase oil pressure at all settings), the 68668 (purple springs that are short and have much less tension than the others), and the 61084 non-color-coded spring that is standard equipment on most regulators. (See photo 12, page 40.)

One of the more common problems with the oil pressure regulators is with the seat that the steel ball contacts every time it closes. The seat is simply a machined aluminum section of the crankcase itself on most engine models, and over time it can become worn, especially if the ball is not contacting the seat dead in the center. 

If oil pressure varies excessively with engine rpm, especially at lower engine speeds, the regulator ball and seat may not be closing properly. Poor contact allows some of the oil to bypass back to the sump when it shouldn’t. (See photos 13, 14 and 15 on pages 40 and 42.)

If the cast aluminum seat has an irregular wear pattern in it, Lycoming recommends rigging up a makeshift tool out of an old ball welded to a steel rod that is thick enough to be struck with a hammer, then inserting the newly made tool squarely against the seat and giving it a couple of sharp hammer strikes to reform the seat, allowing a tighter fit between a new ball and the seat. 

The field method of repairing a worn or non-concentric seat that most mechanics employ is to use the same tool mentioned above, but instead of striking it with a hammer, they use a tiny bit of valve grinding compound on the ball to re-lap the seat. Care must be taken to prevent the compound from getting into any of the oil passageways during the process, but overall this method tends to work well to reform the seat and regain a good seal between the ball and seat. (See photo 16, page 42.)

Some of the earlier engines did have a replaceable seat insert that could be changed out and replaced if it was worn, but the most common seat is the cast aluminum type mentioned above. 


Oil pressure gauge

The oil pressure gauge on many airplane models consists of a mechanically-actuated “Bourdon tube.” The Bourdon tube is a somewhat rigid, coiled, hollow tube. 

The tube is connected to a small oil pressure line and as oil pressure increases, the tube is stretched to a straighter, uncoiled position. The amount that it stretches varies directly with the pressure. An attached needle and gear mechanism allows the varying pressure to be read on the oil pressure gauge. 

These mechanisms can get dirty and stick, or the gearing mechanism can get worn and not indicate correctly. A shaky needle is often caused by a worn gear mechanism in the gauge.

Some aircraft use an oil pressure transducer or sending unit that looks similar to the oil pressure switch used for Hobbs meter installations. It is a unit that has an oil pressure line piped into one side, and electrical wires connected to the other side. Pressure is converted to an electrical signal and wires are run to a gauge that displays the oil pressure reading.

The oil pressure in most Lycoming engines is taken off the top rear accessory case. The oil pressure fitting has a reduced orifice in the outlet to the gauge. This helps prevent catastrophic oil loss if the oil pressure line or gauge begins to leak. Carbon or dirt can sometimes clog the orifice and cause an abnormally low oil pressure reading. 


Troubleshooting oil pressure problems

Most oil pressure problems can be adjusted back to normal with the regulator or traced to a malfunctioning regulator or gauge. Sometimes, the trouble is a little more difficult to repair. 

The first step in correcting abnormally high or low oil pressure should be to double-check the pressure reading with a separate pressure gauge to confirm that the oil pressure really is too high or low. 

Check the oil temperature, too. Low oil pressures will produce increased oil temperatures, and vice versa; overly high temperatures thin the oil and can cause a lower-than-normal oil pressure reading.

Excessive internal engine clearances due to excessive wear or a bearing failure can become so great that the output of the pump is insufficient to fully pressurize the oil system. This is typically a worst-case scenario and lower oil pressure readings occur gradually over time. 

Excessive oil pump clearance between the impellers and the housing can also cause degraded oil pressure output.

Oil viscosity plays a role in oil pressure as well. A slightly lower than normal oil pressure may be caused by using too thin an oil depending on where the plane is operated. 

A clogged suction screen or partially blocked passage between the screen and pump can also cause low oil pressure.

A higher-than-normal oil pressure reading, especially one that occurs suddenly, can be indicative of a blockage somewhere in the system, usually downstream of the pump. Conclusion

Oil pressure readings should be consistently monitored so that any deviation from normal operation can be detected and remedied quickly. Consistent, normal oil pressure from startup to shutdown helps assure that an engine will run reliably for a long time.


Know your FAR/AIM and check with your mechanic before starting any work.  

Jacqueline Shipe grew up in an aviation home; her dad was a flight instructor. She soloed at age 16 and went on to get her CFII and ATP certificate. Shipe also attended Kentucky Tech and obtained an airframe and powerplant license. She has worked as a mechanic for the airlines and on a variety of General Aviation planes. She’s also logged over 5,000 hours of flight instruction time. Send question or comments to . 


Lycoming Mandatory Service Bulletin 518D


Lycoming Service Instruction No. 1565A