Cessna Flap Tracks Inspection & Replacement

Cessna Flap Tracks Inspection & Replacement


Cessna flap tracks eventually wear out, and when they do, it’s an airworthiness issue. Here’s how STEVE ELLS changed four flap supports, more commonly known as flap tracks, on a Cessna 150.


In 1995, Cessna issued Single Engine Service Bulletin (SEB) 95-3. This 27-page bulletin, titled “Flap Support Inspection and Roller Washer Installation,” applies to most single-engine Cessna airplanes including the Agwagon series, the 206/207 heavy haulers and the 210 high performance retractable airplanes. It does not apply to 172R, S; 182S, T; T182T; 206H; T206H or 208 aircraft. Cessna considers SEB 95-3 Revision 1 a mandatory bulletin. 

The initial inspection in the bulletin wants owners to check the flap tracks for damage such as wear, gouges and cracks; and for security of attachment. It also mandates the installation of special stainless steel washers on the inner and outer side of the forward flap rollers. These washers protect the flap supports from wear. 

If the initial inspection shows that the tracks and rollers are in good shape, all that’s required is the installation of the special washers—Cessna Part No. S1450-3S10-032—which have a $2.99 list price. 

Any gouges can be polished out, providing the metal removed doesn’t exceed 0.020 inches in depth. 

Often, due to improper lubrication, dirt and other contamination between the tracks and rollers, the slots in the flap track eventually become oversized. A track is worn out if either slot in the track is wider than 0.6035 inches. 

McFarlane Aviation makes an easy-to-use gauge (McFarlane Part No. 950; cost $41.21) to determine if the flap track slots are worn beyond the 0.6035-inch limit. The following paragraph from the McFarlane website describes the wear process:

“The flap rollers wear into the flap support arms on Cessna aircraft. This wear is caused by the flap rollers due to the asymmetric extension or retraction of the flap during flight. This asymmetry is caused by the inboard or outboard section of the flap leading the retraction or extension of the flap. Many factors, including rusty or damaged rollers or flap track imperfections, can contribute to this condition. This asymmetry causes the rollers to be pressed against the flap support arms (roller end loading) which, over time, causes damage to the flap support arms and structurally weakens the flap.”

Instead of wearing the metal away, the metal at the edges of the track slots gets displaced. This displacement is often called “mushrooming.”

Assessing the flap tracks and getting the parts

Recently I helped Martin Caskey, the local hard-working A&P mechanic at C Aero Services on the Paso Robles Municipal Airport (KPRB), change all four flap supports—often called flap tracks—on the local soaring club’s 1964 Cessna 150 with a 150 hp engine. 

It took longer than we thought it would.

Our inspection showed mushrooming on all four flap tracks and accelerated wear where the flap rollers bore in the tracks at the 20-degree flap extension spot. The tracks were worn out. 

The trusty 150 had an airframe total time of 5,788.5 hours, and the flap tracks had never been changed. The flaps—manually operated in this 150—could still be deployed and retracted at will, but there were obvious signs of wear.

There’s no doubt that some of the wear was due to the fact the 150 had spent the last few years of its life pulling gliders and sailplanes aloft with the flaps at 20 degrees during high-power tow operations at best rate-of-climb airspeeds. 

Previously Martin had replaced the rollers and the associated bushings and washers by installing McFarlane Aviation’s Flap Roller Upgrade Kit (Part No. FLP-KT-1U). This kit includes the special washers called out in SEB 95-3 R1, and all the parts needed to replace all the existing flap rollers and hardware. The roller kit for our 150 cost $476.74. (McFarlane has also developed roller upgrade kits for other Cessnas that cost between $475 and $715, depending on the airplane. —Ed.)

We needed four new tracks. Again, McFarlane Aviation was the place to go. Not only did its FAA PMA tracks have improvements over the original tracks, they were markedly less expensive. 

We bought four MC0523231-14 flap tracks at a price of $237.15 each, for a total of $948.60. The McFarlane tracks are made of material that is an improvement over the original tracks. According to McFarlane, its tracks are 20 percent stronger which translates to six times the fatigue strength. They’re also a lot less expensive than the Cessna parts which retail for over $600 each. 


Removing a flap track

There’s no easy way to remove a flap track. First, the flaps must be removed; then all the upper and lower rivets that hold the flap cove sheet metal in place must be carefully drilled out. This exposes the bracketry that secures the flap tracks. 

Each flap track for our C-150 is secured by 9 1/8-inch diameter AN470AD-4 rivets. We drilled those out and removed the tracks. On the workbench we aligned the old and new tracks by running a roller back and forth in the slots when the tracks were clamped loosely together. 

Once the roller moved smoothly, the clamps were tightened. Then, using the old tracks as drill guides, holes were drilled in the new tracks.


Installing the new flap tracks

After sliding the new tracks into position in the supports, we installed and bucked new rivets. 

Following the installation, Martin and I riveted the flap cove sheet metal back in place and installed the flaps after we had cleaned and lubricated the needle bearings in each roller with grease. 

There are no specific instructions in many Cessna single engine maintenance manuals about the proper lubrication of flap rollers. The rollers in the McFarlane upgrade kit roll on needle bearings, which should be removed, cleaned and greased periodically. 

Squirting a general lubricant on the outside surface of the roller may cause the roller to slide—instead of roll—in the flap track grooves. Rolling is low friction; sliding is high friction and contributes to accelerated flap track groove wear. 

McFarlane also has a flap roller installation tool (McFarlane Part No. 970; cost $37.32) that makes it easy to align the rollers. It’s very helpful when working through the small access holes in the flap when installing the aft flap rollers.


Changing four flap system pulleys

The flap actuating cables from the manual flap handle are routed aft from the handle to four pulleys located in the belly of the airplane. The cables turn 90 degrees at pulleys; two cables are routed to the left flap and two to the right flap. 

There are two more 90-degree cable turns: one each just inside of the cabin wall where the cables are turned to run up to the wing root, and one in the wing root where the cables are rerouted to run out the inside of the wing to the left and right flap bell cranks. 

In our 150 project, the flap cable tension rigging was complicated by four worn pulleys. Martin and I decided to change the pulleys (Cessna Part No. S378-2) in the belly due to wear in the pulley grooves. 

At the end of the job, the tracks were stronger; the needle bearings in the rollers were properly lubricated; the pulleys in the system were pivoting on their bearings; and the flap cable tensions were correct. We felt that the flap system was now in better-than-new shape.

The parts costs totaled $1,654. Labor man-hours added up to 48. That may seem like a lot of money to spend on a flap system that seemed to be working, but according to the manufacturer, the tracks were worn out. To maintain airworthiness, they needed to be changed. The entire flap system in this hard-working 150 is again airworthy. 

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  


McFarlane Aviation Products
– CFA supporter



C Aero Services



Single Engine Bulletin
(SEB) 95-03 Revision 1

“Flap Support Inspection and
Roller Washer Installation”


CessnaFlyer.org/forum under “Magazine Extras”

My Engine is 50 Hours From TBO…

My Engine is 50 Hours From TBO…

When it comes to what to do when your engine reaches TBO, your choices range from doing “everything” to doing “nothing.”


The following is an excerpt from Bill Ross’ 144-page book “Engine Management 101.” Published by Superior Air Parts, Inc., “Engine Management 101” is a compilation of what Ross has learned during his 36-plus years of experience as a pilot, aircraft owner, piston aircraft engine industry leader and FAA A&P/IA.   

TBO —what does it really mean? 

Today, there are many in the industry making a case for flying the aircraft until it breaks and not necessarily adhering to manufacturer’s recommendations for continued airworthiness. To me, that’s just asking for trouble. 

How do you know when the aircraft will “break?” Will it be on short final at your home airport, or at night, in the clouds, with your family on board? Is the risk worth it to you? I certainly hope not. 

My opinion is you can safely fly past TBO without consequences if you and your maintenance provider follow the engine manufacturer’s recommendations.

The ABCs of TBOs

Let’s look at the term “time between overhauls” (TBOs). The FAA requires manufacturers to publish a TBO for each of their engines. These aren’t numbers that are pulled out of a hat. The engine manufacturers establish these recommendations based on typical maintenance and typical engine operation. 

Engines are required to have both an accumulation of actual operating time and calendar time recommendations. Mistakenly, many pilots try to “extend” their engine’s overhaul—and the cost thereof—by not flying as often as they should. The fact is, lack of consistent use is probably one of the worst things you can do to an aircraft engine. 

Aircraft engines that are sedentary for many months, and sometimes years at a time, are more likely to have internal damage than those that are maintained and flown regularly. Most engine manufacturers recommend that if the engine is going to be inactive for six months or longer, it should be preserved in accordance with their respective instructions. 


TBO: Your time has come

One of the questions I get asked most frequently about TBO is whether an owner should overhaul or replace their engine. It’s a good question, and it has more than one answer. Fact is, when your engine reaches overhaul time, you basically have six choices:  

1) Purchase a new engine.

2) Purchase a rebuilt engine.

3) Have your engine overhauled.

4) Patch the engine of leaks, address any low compressions and accessory issues. 

5) Wait too long.

6) Do nothing. (Really. That is an option.)

OPTION 1: Purchase a new engine.

When you purchase a new engine, every part is new and meets factory-new specifications with zero time, a new serial number and a factory-new warranty. 

Aside from those points, there is really no technical benefit to the new engine. It will not necessarily provide you with any more power, smoothness, better performance or longer service life than any of the other options we will discuss.  

OPTION 2: Purchase a rebuilt engine. 

Rebuilt engines are different from overhauled engines, even though people often use the terms interchangeably. The rebuilt engine is assembled at the engine’s original manufacturer using various parts from the manufacturer’s used/reclaimed stock. 

When rebuilding an engine, the manufacturer is not required to disclose the total hours (i.e., total times) on those “stock” items. Therefore, you could have a crankshaft or crankcase that has a lot of hours or several previous TBO intervals on it. 

Nevertheless, rebuilt engine components must meet factory-new fit tolerances, but specific parts can be machined undersized to meet specifications. There is nothing inherently wrong with this practice, but it could result in an unusable crankshaft at the next overhaul. 

Rebuilt engines are issued new serial numbers and granted zero-time status by the manufacturer. 

OPTION 3: Have your engine overhauled.

Historically, an engine overhaul has been the most economical option for aircraft owners. During an overhaul, your original engine is sent to a third-party overhauler, where it typically receives new cylinder assemblies, hardware, gaskets, bearings and other piece parts. 

The overhauled engine is not granted zero-time status. The engine’s total time is continued from the point of overhaul. For example, the engine may have 2,000 hours and zero time since major overhaul. The engine still has 2,000 hours total time. 

An overhauled engine, if worked up by a reputable facility, can greatly enhance the aircraft’s value. Why? Simply because it keeps the engine/airframe serial numbers as matching pairs. That means a lot to some owners.

OPTION 4: Patch engine leaks; address low compressions and accessory issues.

Patching the engine should be only considered if the internals of the engine are determined to be in good condition. That means no metal in the filter, and oil consumption is within the limits set forth by the manufacturer. 

Most aircraft engine failures that I have investigated or have performed analytical inspections after the fact, failed due to either a malfunction in the fuel delivery or ignition system. Therefore, always follow the manufacturer’s recommendations for continued airworthiness for critical items including the magnetos, alternator and the fuel delivery system. Like the engine as a whole, each of these components have specific service intervals that should be followed. 

For example, ignition systems typically have 500-hour inspections, and some have requirements for overhaul after four years in service or five years from date of manufacture. 

Remember that doing a preflight runup and magneto check at the end of the runway is not always an indicator of good ignition system health. Preventive maintenance can go a long way in providing enhanced reliability and safety.

OPTION 5: Wait too long.

One of the airplanes my father and I own had the original engine it was delivered with back in 1966. When we purchased the aircraft, it only had about 1,200 hours total time. Many of you might think, “Wow, it had lots of time left on the engine.” Which it did… 

…but we were continually repairing oil leaks, reworking accessories and worrying about becoming stranded away from home base. 

This continued for a number of years until one day I was performing an oil change. I invited my daughter to ride with me around the patch in order to warm the engine oil. We came back, landed and removed the cowling for draining the engine oil. 

When the oil began to flow, I noticed what looked like pieces of metal flowing from the drain hose. That’s not good. I pulled the oil screen and we could almost read the part numbers for the metal coming from the engine. 

I remember the look on my father’s face. It wasn’t a look of financial distress, but rather, relief. Now we had a valid excuse to overhaul the engine. The trouble here is we could have waited too long. 

Not only was it a risk to our safety to push the envelope on this engine, but also by continuing to fly it, we could have done irreparable damage to the engine that would have been more costly to repair than a standard overhaul. 

OPTION 6: Do nothing.

You read it right: the last option is to do nothing. By definition, TBO is just a “recommendation.” It’s not a law. Many engines go beyond TBO and perform very well. 

But before going that route, you need to have a thorough evaluation of the engine’s current state. Questions that I ask of owners that question me about going beyond an engine’s TBO are:

1) What is the calendar time since the engine was new or last overhauled?

2) What is the oil consumption?

3) Do you have any persistent oil leaks?

4) Have you discovered any wear material in the oil during analysis? 

5) What is the reliability of the accessories including the magnetos, alternator, carburetor or fuel injection system?

6) What price do you put on your peace of mind?

7) What price do you put on the safety of you and your passengers? 

While there are plenty more questions I could ask, these seven hit the high points when it comes to an engine’s overall health—or lack thereof.

My engine has plenty of life left!

It may well, but you should also ask yourself this question: what is the calendar time since the engine was new or last overhauled? 

Why does that matter? Remember, inactivity of an engine can be very damaging due to internal corrosion. That fact than an engine has low operational hours does not mean a thing to me.

For example, look at the ads that list aircraft for sale. I have never once seen an ad that actually stated the engine’s calendar time. You see many with 500 or 600 hours since major overhaul or since new all the time. 

What buyers should be asking is, “What is the engine’s actual calendar time?” and  “How long has the engine been sedentary?” Generally, you would like to see the aircraft flown at least a couple of times per month. 


“Oil, that is...black gold. Texas tea...”

Another critical thing that helps determine the overhaul health of an engine is its oil consumption. Does it have any persistent oil leaks? Or have you discovered any wear material in the oil during analysis? Regular oil analysis can be a very helpful diagnostic tool.

With regard to oil consumption: are you constantly filling the oil every time you fill up with fuel? If so, your engine is likely a candidate for replacement or overhaul. Increased engine oil consumption could be the result of actual engine usage, leaks or a combination or both. 

An old engine that is beginning to show these symptoms is probably getting close to needing overhaul, replacement or significant repair. The question to ask yourself is: how long can I continue to bale the engine together?

To TBO and beyond

I am not advocating that you rigidly adhere to your engine’s recommended TBO numbers, but the manufacturer is required to provide one as a point of reference. 

Clearly, you can safely fly past TBO, provided you follow the manufacturer’s recommendations for determining continued airworthiness of the engine. Those owners and maintenance providers that follow the proper maintenance guidelines will beat others to the engine’s TBO numbers and beyond through overall lower operating costs and improved safety. 

Basically, if your engine is not producing abnormal wear metal, has good compressions, does not consume oil at an alarming rate and is maintained in accordance with manufacturer’s instructions, more times than not, you can safely fly past TBO without any issues. And there are folks who do it day in and day out. 

My point here is that you can expect long life out of your aircraft’s engine if you take care of it and do the maintenance and inspections when and how the manufacturer recommends. 


Bill Ross is a graduate from the University of South Alabama and was employed by Continental Motors for 15 years holding positions in engineering, analytical, air safety and technical product support. Bill is now Vice President of Product Support for Superior Air Parts and committed to the company goal of making flying affordable. When not working at Superior, Ross can be often found flying his family’s 1941 Boeing Stearman, working on antique aircraft or exposing young people to the joys of flight and potential careers in aviation. Send questions or comments to .