Preventing Loss of Control: Maintenance Issues

Preventing Loss of Control: Maintenance Issues

Loss of control is a hot topic among the NTSB, FAA and other aviation organizations that promote aviation safety. 

 

Last year, the NTSB named the prevention of loss of control in flight in General Aviation as one of its “Most Wanted” transportation safety improvements. The NTSB report issued in 2015 stated that “between 2001 and 2011, over 40 percent of fixed wing GA fatal accidents occurred because pilots lost control of their airplanes.” 

This is unacceptable and mostly preventable. All pilots should be aware of the possibility of loss of control and take the time to review actions to prevent it. 

One way is to study flight manual procedures specific to the aircraft you fly. Another is to be aware of common situations that can contribute to loss of control. As a former air carrier pilot, air taxi pilot and mechanic with inspection authorization, I will focus this article on equipment and mechanical malfunctions that can also contribute to loss of control. 

 

Preflight actions

As aircraft control systems, flight management systems and electronics have advanced to make the task of flying easier, it is still necessary to have sufficient skills not only to fly the aircraft but to do all of the tasks we learned to do as a student pilot. 

Preflight actions, and proper flight planning—such as checking the weather, notams, aircraft preflight, weight and balance checks and the use of checklists—are all part of the job of flying. Without regard to who actually does all these tasks, as pilot in command, you are responsible for your actions in the operation of your aircraft. Even if it’s just a local flight and you are in hurry, don’t shortcut the process. 

How does this relate to loss of control? Preparing to fly a plane is a process of building blocks, and each item on the preflight list is important to the safe operation of an aircraft. The winter season can bring about additional challenges as cold weather, snow and ice can contribute to accidents because of a rushed or skipped preflight. 

Consider the flight crew that attempted to take off with control locks in place and crashed. Did someone actually do a preflight check and didn’t notice the gust locks were in place? And then, in addition, missed an important item on the pre-takeoff checklist—flight control check? 

Several years ago an aircraft was destroyed when a screwdriver was used in place of the control lock mechanism normally found with Cessna aircraft. While the control lock mechanism is not a required piece of equipment for flight, it is definitely not safe to use a screwdriver as a substitute. You can certainly duplicate the original Cessna-supplied control lock, or make one of your own—just be sure that it is marked is such a way that it is not overlooked during preflight. 

I have written in the past about checking an aircraft after maintenance, and again it is the pilot in command that has the last word as to whether an aircraft is acceptable for flight or not. Occasionally, errors are made and flight controls are improperly rigged, with the worst scenario being a control rigged in reverse. 

This actually happened a few years ago, when an aircraft elevator trim control was rigged in reverse. The aircraft was taken up for a test flight with the pilot not realizing this significant error. The autopilot was engaged, altitude hold selected; and the elevator trim and elevator control opposed each other until the autopilot disconnected in an extreme out-of-trim condition with suspected full elevator input to oppose the mis-rigged trim. The aircraft was not flying high enough to allow sufficient time for the pilot to correct the problem and the aircraft crashed. 

While this would be a difficult error to detect on a preflight without the help of a second person, it is something you must be aware of any time an aircraft flight control has had recent maintenance performed. Do you as a pilot not only move the flight controls on preflight, but actually confirm that the controls work in the proper direction? Which way should the aileron move when the control wheel or stick is moved? Are you sure? 

We will never know the exact details, but it’s entirely possible that these items in the building-block approach to flight were completely bypassed. 

How about the elevator and rudder, and the way that they move in relation to the control movement in the cockpit? Are the controls smooth, or are there unusual noises or resistance to full control movement during a preflight ground check of the flight controls? 

Winter weather can add environmental concerns such as snow or ice, which can build up on flight controls when the aircraft is parked and restrict full control movement or even jam a control in a partially deflected position. 

When preflighting your aircraft in
winter, check flap travel incrementally;
if the flaps are obstructed by snow or ice, or one flap is blocked from movement by ice, the flap actuator mechanism can be damaged and lead to an asymmetrical flap condition preventing full control of the aircraft on takeoff.  

 

Flight control maintenance

Lack of proper flight control maintenance can lead to unauthorized patches or repairs; broken, cracked or missing parts (such as elevator and rudder tips); and slack control cables. 

Good housekeeping

Errors occurring during maintenance can usually be identified by a thorough preflight. A missing cotter pin on elevator cable attachments, a tool or part left behind after maintenance, and any missing or incorrect fasteners attaching the tailcone to the fuselage will likely be detected during a thorough preflight. 

An extreme example of just plain bad housekeeping that cost two people their lives is attributed to a WD-40 can found lodged in an aircraft tailcone after an accident. There have been other bad housekeeping situations, too, such as plastic water bottles and even a flashlight discovered on the cockpit floor ahead of the rudder pedals. 

Never be casual about a preflight, especially after maintenance. 

Primary flight controls

In the case of unauthorized repairs, at least one popular aircraft manufacturer, as stated in their maintenance manual, does not allow stop-drilling of cracks in any primary flight control and does not allow scab patches, either. The control surface must be re-skinned, primed, painted and then balanced to be considered an authorized and airworthy repair. 

Flight controls must be inspected, repaired and returned to service by following all up-to-date manufacturer’s instructions exactly with no shortcuts. 

It is without question that any damage to a flight control requires maintenance, or, at the very least, an inspection by a licensed mechanic to determine if repairs are in order or the control is okay for return to service. 

While working for an aircraft manufacturer’s service center, I recall a situation where a pilot flew in with a complaint that his right aileron was binding and making a scraping sound when he operated the controls. 

The mechanics took a look at the aileron and discovered damage to the underside of the wing and aileron which was caused by the pilot. He admitted that he had struck a tree on a night approach to landing several weeks earlier. This pilot had been flying the airplane multiple times in this condition and had no idea what the extent of the damage was. 

 

Cables

Cable tension is another maintenance issue that must be considered as important to proper flight control operation. When the weather turns cool, control cable tension is reduced because the aircraft and the cables shrink slightly. Slack in the cables will create lost motion and reduction in control surface deflection. This could result in your inability to obtain a perfect landing. 

In the case of extreme weather conditions, when full control deflection is necessary (such as in a strong crosswind) control cable slack could contribute to an accident. Consider checking and adjusting control cable tension when the aircraft is exposed to extreme weather conditions.

 

Autopilots

As aircraft become more technologically advanced, autopilots, flight management systems and avionics all enter into the discussion of loss of control. In order to rely on an autopilot, it must have regular maintenance checks and service—and, as part of that service, control cable tension and proper control travel (rigging) must be within limits for the autopilot to perform properly. 

Autopilots and associated avionics certainly enhance safety by reducing the pilot’s workload, but at times, pilots—especially during single pilot IFR operations—can become task-saturated. Mix in bad weather, a long duty day, extensive holding, being low on fuel… and things can go bad quickly. You must know your equipment and be very familiar with all modes of operation. 

In my travels as an air carrier pilot I have overheard other pilots’ statements regarding autopilots including, “Why is it doing this?” and “Look what it’s doing now.” While this may be amusing to some, the pilot in command, not the autopilot, must be in control at all times. Take the time to study, ask questions and really dig into the manuals to find out why it’s doing what it’s doing. 

Many new aircraft are now being delivered with autopilots and flight management systems as standard equipment, and accident reports seem to suggest that some pilots fly into conditions that they are not capable of handling on their own. 

Autopilots have limits, and when weather conditions get bad and those limits are exceeded (such as moderate to extreme turbulence, or icing conditions), expect that the autopilot will disconnect and leave the flying to you. 

Never use an autopilot to fly into conditions that you are not capable or experienced enough to handle when hand-flying the aircraft. Realize your limits, and give yourself an out if conditions get bad so you may live to fly another day. Comply with manufacturer’s maintenance and service recommendations for autopilots to ensure that your autopilot functions correctly when you need it the most. 

Prevention is an ongoing process

Recurrent training, studying the manuals on autopilots, and knowing how to operate your avionics and flight management systems can help reduce stress, especially in high-workload IFR environments. 

Loss of aircraft control can happen as a result of many factors, but it is a given that proper maintenance, preflight actions and always performing a complete flight control check prior to each and every takeoff can go a long way toward preventing loss of aircraft control. 

Michael Berry, a former aircraft repair shop owner, is a multi-engine rated ATP (757/727). In addition, he’s a turbo jet flight engineer, an A&P/IA mechanic, airplane owner and 121 air carrier captain. Berry has 15,000-plus pilot hours. Send questions or comments to .

Resources

Further reading

NTSB 2015 Most Wanted Transportation Safety

Improvements “Prevent Loss of Control in Flight in General Aviation”

CessnaFlyer.org/forum

2016 Most Wanted list
Read more...
Creating a “Mountain Goat” 182, Step One: Off-airport Landing Gear

Creating a “Mountain Goat” 182, Step One: Off-airport Landing Gear

With a successful top-end inspection completed, STEVE ELLS guides a new owner through the first steps to make his Cessna 182 a reliable backcountry plane.

Bill hangars his 1966 Cessna 182J Skylane in the hangar next to mine at the Paso Robles Municipal Airport (KPRB).

Bill is tall, drives a pickup, is comfortably retired—and enjoys flying. He has owned his 182 for four years. It has carried him on cross-country flights to Kansas, Phoenix and San Diego. Since I’ve known him, it seems most of his flights consist of short day-VFR trips to take his wife for lunch.

Last September I saw that Bill’s hangar was open, so I stepped over to catch up. Bill told me that Greg, who was there with him, wanted to buy his airplane. 

Bill hadn’t mentioned wanting to sell. Interested, I listened. 

Bill introduced me as a guy that knew a lot about Cessna 182s. Greg wanted my opinion on the engine in Bill’s airplane, since Bill had told him it had 1,720 hours since its last rebuild. In other words, it was 20 hours past what the manufacturer, Continental Motors, printed as the recommended TBO. 

Bill told him that the engine was running fine; it always started right up, made good power, the oil analyses were always clean and that it had been well taken care of. Bill asked me to inspect the engine to determine if it was airworthy. I agreed to take on that task since the protocol is well defined.

Continental cylinder inspection

In 2016, Continental Motors released Publication M-0, “Maintenance Manual: Standard Practice for Spark Ignition Engines.” This manual is the go-to source for guidance when performing inspections, maintenance and diagnosis on Continental piston aircraft engines. (Make sure you have the most current revision. At press time, the latest iteration is dated July 2017. —Ed.)

Chapter 6-4.11 is titled “Cylinder Inspections.” Sub-chapters include visual inspections, differential compression tests, cylinder borescope inspections, cylinder-to-crankcase mounting inspections, baffle inspections and cowling inspections.

I use both a differential compression test with calibrated orifice and a borescope to determine cylinder health as mandated by M-0. Since the guidelines in the M-0 differential compression chapter differ greatly from the guidelines in FAA Advisory Circular AC 43.13-1B, titled “Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair,” these tools are essential when conducting the Continental cylinder testing. 

I own an Eastern Technology E2M differential compression tester. Aircraft Tool Supply also sells a house-branded differential pressure tester, which they call the 2EM.

I used a VA-400 rigid USB borescope from Oasis Scientific to inspect the valves in accordance with the M-0 protocol. This borescope connects to my laptop which allows me to create a file for storing photographs of everything I see during the inspection.

I performed the inspections of the cylinders in accordance with the chapter and found the compression readings acceptable at 72, 70, 72, 70, 68 and 72/80. A thorough “scoping” inside each cylinder showed no scoring on the cylinder walls, normal lead deposits on the piston crowns and no indication of any valve problems. 

In addition to the cylinder inspection chapter, M-0 also provides guidelines for determining if there are excessive combustion gases escaping past the rings. The test procedures are in Chapter 8-9.1. Bill’s engine also passed this test.

Based on these tests, I concluded that the top end of the 230 hp O-470-R engine in Bill’s airplane was airworthy. Within a week, Greg and Bill had agreed on a price and the airplane (and the hangar) changed hands. 

Greg’s goal

Greg owns a contracting business on the central coast of California. His business is thriving, and he works hard. When he can get away, he enjoys spending time at his cabin high up in the Monache Meadows Wildlife Area in the Sierra Nevada. 

He told me he yearned to get his family, including his 92-year-old mother, up to the cabin often but hasn’t been able to because of the nearly seven-hour drive to get there. Greg figures a flight in his 182 will take no more than 90 minutes. There’s just one catch: the only landing strip is a gravel/sand runway on the edge of a dry lake at 8,000 feet msl. 

I asked Greg why he bought Bill’s 182. Here’s what he said: “Lots of things. The two doors allow me to have my 92-year-old mother go along—it would be too difficult to hop over her in a Piper Warrior/Cherokee.”

“The 182 has horsepower to deal with high altitude better,” he continued. “The 182 is wider and carries a larger payload; my family are all tall and large people.”

“The high wings allow me to clear tall brush on the side of runways: Lone Pine (O26, located 40 miles south of Bishop) was scary with the Warrior I used to own.”

Greg put in a great deal of thought and flight time preparing to fly in to O26 this summer after the snow melts. Within a few weeks after the sale, he had flown to the east side of the Sierra and hired Geoff Pope, a CFI based at the Bishop, California airport (KBIH) for mountain flying instruction. He also took his 182 to the Big Bear City Airport (L35) to learn how it handles doing touch-and-goes at 6,732 feet msl. 

Big tires

During our initial conversations, I suggested that Greg set aside some cash to install a bigger nose tire since his 1966 182 didn’t come from the factory with the left and right firewall reinforcing channels. 

These channels, which reduce the odds of bending the firewall, can be retrofitted to all 1962 through 1970 aircraft by incorporating Cessna service kit SK182-44C in accordance with single engine service letter SE71-5. The kit had not been installed on Greg’s airplane. Cessna installed the channels at the factory beginning in early 1970 with Serial No. 182 60291. (For more information on firewall reinforcement, see Steve’s Q&A column in the January 2018 issue of Cessna Flyer. —Ed.)

I told Greg that his 182J was a good airplane and that it could safely operate out of the strip by his cabin if he factored in variables such as winds aloft, density altitude, weight and balance and was prudent about risk management. 

We decided that the most immediate step in converting his 182 for safely flying into high-altitude unimproved strips like the one near his cabin was to install bigger tires. 

 

Nose fork upgrade

The standard sized nose tire for 182s like Greg’s is a 5.00-5 tire with a 6-ply rating. During my search for bigger tire solutions, I found that the Cessna parts manual does show the parts for what’s called a Heavy-Duty Nose Gear installation for a 6.00-6 tire, but it requires a different hub and nosegear barrel assembly. 

During Greg’s research, an acquaintance suggested that a Cessna 310 nosegear strut and fork would work. 

Due to the time and expense of searching out parts and approval for the installation of surplus or salvage parts, we decided to seek the advice of Jim Hammer at Airglas Engineering in Anchorage, Alaska. 

Airglas sells an STC-approved large nosegear fork that can be installed on all existing nose landing gear barrels. Large nose forks are available for Cessna singles from the 150 through the 207 and for Piper singles including PA-28-140 through -235, and PA-32-260 and -300. The kit includes the large fork, a new axle and a new strut block. 

The Airglas website contains drop-down menus for each approved model. Topics include pictorial installation instructions, EASA approval docs, STC docs and detailed step-by-step installation instructions.

Greg and I liked what we heard from Airglas and placed an order with Hitchcock Aviation in Star, Idaho. They assembled all the needed hardware, STCs and installation instructions before shipping the package to Greg. 

Jesse Bennett, a local A&P, removed the front strut assembly and disassembled it. A machinist cut the strut tube in accordance with the Airglas instructions and installed the mounting block on the strut. Next, the fork was bolted on and an 8.00-6 6-ply tire and new tube were mounted on a new Cleveland 40-75D wheel assembly. The nosegear strut was reassembled and serviced.

That took care of increasing the footprint of the nose tire. What about the mains?

 

Working on the mains

The nosewheel assembly, two new heavy-duty double-puck black anodized brake assemblies (Alaskan Bushwheel Part No. 30-52N) and the installation and Instructions for Continued Airworthiness (ICA) manual were purchased from AirFrames Alaska. Installation approval for the wheels and brakes is by Supplemental Type Certificate (STC) SA02231AK held by F. Atlee Dodge in Anchorage, Alaska. 

Greg bought 8.50-6 tires and new tubes for the main landing gear. Parts and approval costs totaled just under $6,000. The strut modification, the installation of the new larger brakes, the block and fork, and the new tires and tubes all happened over the course of one day with hours to spare. 

The new landing gear parts add about 25 pounds to Greg’s aircraft empty weight. The bigger tires and beefier gear also increase drag—so he won’t see the normal 135-knot cruise speeds. But he will be spending more weekends with his family in the mountains; not a bad exchange.

The larger tires provide around 4 more inches of ground clearance and a larger tire footprint. The increased “float” of the larger nose tire drastically reduces the odds of nosegear (and firewall) damage due to uneven runway surfaces. 

After May, when all the snow has melted and the “runway” has dried out, I expect to see Greg gently settling his mother into the copilot seat of his “mountain goat” 182. Next stop: a cabin high up in the Sierras. 

Greg bought an airplane that fit his mission’s needs—and then modified it to increase utility and safety. As a result, he can continue to devote the time needed to care for his contracting customers and spend more “cabin” time with his family. Isn’t that what airplanes are for?

 

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

 Resources

DIFFERENTIAL CYLINDER COMPRESSION TESTERS

Aircraft Tool Supply Company
 
Eastern Technology Corp.
 
VA-400 RIGID USB BORESCOPE 
Oasis Scientific, Inc.
 
NOSE FORK AND OTHER LANDING GEAR UPGRADES 
Airglas Engineering 
 
Hitchcock Aviation, LLC
 
HEAVY-DUTY BRAKE ASSEMBLIES 
AirFrames Alaska
 
STC SA02231AK 
F. Atlee Dodge
 

FURTHER READING

Publication M-0, “Maintenance Manual: Standard Practice for Spark Ignition Engines”
Continental Motors Group
 

MAGAZINE EXTRAS

FAA Advisory Circular AC 43.13-1B
“Acceptable Methods, Techniques, and Practices – Aircraft Inspection and Repair”
 
Cessna Single Engine Service Letter SE 71-5
CessnaFlyer.org/forum under “Magazine Extras”
Read more...
Big-airplane Features for a Small-airplane Price: The Cessna 175

Big-airplane Features for a Small-airplane Price: The Cessna 175

Cessna introduced the 175 hp, four-seat Cessna 175 in 1958; with the goal of filling the gap between the 172’s price and the 182’s performance. The 175 garnered positive initial reviews. Yet only six years later, the model was discontinued. So, what went wrong? 

Just over 60 years ago, on March 22, 1958, Cessna offered its first Cessna 175 for sale. Then, as now, marketing departments used flowery language to sell the dream of “the family airplane.” 

A big and beautiful two-page ad in the April 1958 issue of Flying offered readers the “big, beautiful” new “Power-Geared” Cessna 175. The 175 promised “big-airplane stability, big-airplane comfort, big-airplane speeds”—but for a small-airplane price.

On the surface, the 175 seemed to fit perfectly in the Cessna lineup. 

At the time the 175 debuted, the 172 was Cessna’s entry-level model (the two-seat 150 wasn’t introduced until late 1958). The 182, though quite capable and roomy, was a significant step up from the 172 in both price and performance.

In 1958, a 172 cost $8,995. A standard 182 was $14,350. The deluxe 182 Skylane was $16,850. The 175, priced at only $10,995 while offering “big-airplane” features, seemed to be what General Aviation buyers desired. Flying reviewed the 175 in July 1958 and deemed it to be “an answer to a market requirement—a constructive answer.”

However, after only a few short years, the market soured on the Cessna 175. The last aircraft carrying the 175 name were produced in 1962. 

A close relative of the 172

At a distance, it’s difficult to distinguish a Cessna 175 from a Cessna 172 of the same era. This is especially true for earlier 175 models, before the 175A adopted a noticeably “humped” cowl. The 175 and 172 airframes were developed concurrently, with extensive parts commonality. 

Delays with the Cessna 175’s newly-developed Continental GO-300A powerplant meant that the 175 debuted two years later than the Cessna 172 and 182, which were both first sold in 1956. 

The 175 prototype took to the skies over Wichita April 26, 1956. The Cessna 175 received type certification on January 14, 1958. An aggressive schedule brought the aircraft to market by late March 1958. 

 

Model evolution

The 175 and 172, though extremely similar when viewed from across the tarmac, do exhibit differences, especially under the cowl and in the cabin. 

Early straight-tail 175s and 172s (pre-A models) have the same fuselage dimensions. However, the firewall position and firewall structures differ. 

The 175’s firewall is a stepped design, rather than the flat firewall of the early 172. The 175’s firewall is further rearward on the fuselage than that of the 172, allowing for a longer, more gradually-tapered cowl with larger inlets for cooling air. The cowls of early 175s appear more like those found on Cessna 182s.

The position of the 175’s firewall affects the position of other internal fuselage components. The instrument panel is correspondingly further rearward, in a wider area of the fuselage. Cessna engineers took advantage of this increased panel width and designed a new instrument panel exclusive to the 175; the early 172’s “shotgun panel” layout was not used. 

The 175’s instruments are clustered on the left side of the cabin, in clear view of the pilot. Though not a quite a linear six-pack arrangement, the 175 has a modern-looking instrument panel. The instrument panel layout was “easy-to-work, easy-to-read,” according to Cessna’s marketing. 

In 1960, the Cessna 175A—as well as the 172A—received Cessna’s new swept-tail design, paired with the “fastback” fuselage. The 175A and later models are fitted with a distinctive “humped” cowl. 

The 172B borrowed from the 175’s design: Cessna adopted the stepped firewall of the 175, a longer engine mount and cowl, and also changed the instrument panel layout to match the 175’s. 

The 172B and 175B fuselages—and in fact, the entire airplanes—are dimensionally nearly identical.

The 175’s wing structure is very similar to that of the 172, with differences in the internal inboard third of the wing to account for the fuel tanks. 

 

Fuel

The 175 has two tanks, one in each wing, that hold a total of 52 gallons of fuel; an upgrade from the 42 gallons of the 172.

Due to the location of the fuel pickups in the tanks, only 42 of the 52 gallons is usable in all flight conditions. The 175’s POH states that an additional nine gallons are usable in “level flight.” However, the 175’s TCDS carries a rather ominous warning: “The Models 175A and 175B fuel system does not comply with CAR 3.433 and 3.434 for horsepower greater than 167 at the best angle of climb which is the most critical attitude.”

 

Options

The deluxe trim model offered from late 1959 onward was called the “Skylark”—all Skylarks are 175s, but not all 175s are Skylarks. Some were fitted with Levelair T-2 or Tactair T-3 autopilots. 

The 175 could be ordered as a seaplane, also. This option boosted gross weight by 100 pounds for the 175A and 175B.

In addition, an 18-gallon auxiliary tank was available for the 175 as a factory-installed option. The tank was installed on the baggage compartment floor with a filler neck on the right side of the fuselage. An electric pump connected the tank to the right wing tank.

Powerplant

As the 175 was being developed, Continental Motors offered Cessna the exclusive use of a new high-rpm 175 hp variant of the O-300. This new powerplant, which would become the Continental GO-300, promised increased performance with a negligible weight penalty. 

According to a July 1958 Flying review of the 175, Cessna engineers debated whether the high-rpm engine design would be better served by connecting a smaller-diameter propeller directly to the crankshaft or by gearing down to a larger prop. Connecting the propeller directly to the crankshaft in a standard arrangement would be no doubt simpler mechanically, but the geared reduction drive offered the lure of more efficient operation, especially at takeoff and climb speeds. They chose to use a geared drive. 

Cessna Flyer contributing editor and A&P/IA Steve Ells explains how it works:

“The reduction gear assembly consisted of spur-type gears with the propeller shaft located above the engine crankshaft centerline. The propeller’s center was approximately nine inches above the center of the crankshaft. This arrangement enabled the installation of a much longer propeller than was possible in any direct-drive engine. The Cessna 175 landplane swung an 84-inch McCauley prop that produced more thrust than the 172’s 76-inch propeller. 

The offset of the reduction drive still provided the required flat nose tire and flat strut prop-to-ground clearance distance mandated by airplane certification regulations. An enormous 90-inch prop was approved on the 175A and 175B when on floats.

A propeller-to-engine reduction ratio of 0.75 provided 2,400 prop rpm at the takeoff power setting of 3,200 crankshaft rpm. At the recommended cruise rpm of 3,000 on the tachometer, the prop settled down to 2,250 rpm. This slower prop speed resulted in lower prop-generated noise at both takeoff and cruise power settings.”

The 175 hp GO-300A spun at a maximum of 3,200 rpm; noticeably faster than the non-geared O-300 which redlined at 2,700 rpm. The difference in engine rotational speed had a price. While the O-300 had a TBO of 1,800 hours, the GO-300s found in 175s had a TBO of 1,200 hours. 

The GO-300A of the early 175 was replaced by the GO-300C and -300D in 1959. The last 175s used the GO-300E and swung a constant-speed propeller. 

The decision to use the high-rpm GO-300 engine and geared reduction drive would ultimately determine the success of the 175 and Skylark names. 

Performance

The most noticeable difference between the 175 and 172, aside from the engine, reduction drive and panel layout, is their relative performance. 

Steve Ells found this to be the case several decades ago: 

“In 1985, I was dropped off with a box of tools at an unimproved strip across from Kenai, Alaska, on the west side of the Cook Inlet to troubleshoot engine problems in a customer’s Cessna 175. I loosened up a draggy exhaust valve with a liberal dosing of Kroil penetrating oil before flying back. 

Although the inlet is less than 30 nm across at that point, I knew if I had to ditch in the cold waters I was a goner, so I climbed up to 8,500 feet before turning toward home and the other shore. 

The GO-300 never missed a lick and I was very impressed with how much more power it seemed to have versus the 172s I have flown previously.” 

Pilots with time in unmodified straight-tail 172s know that they’re sweet-handling aircraft; they also realize that the 145 hp Continental O-300 gives merely adequate performance. Cruise speeds are typically around 120 mph tas (104 ktas). Though early 172s are light airframes (over 300 pounds lighter than today’s 172s), their low MTOW of 2,200 pounds limits payload. After filling the tanks, about 640 pounds are left for passengers and luggage. 

A stock 175 weighs about 100 pounds more than its 172 counterpart, but that is offset by a 150-pound increase in MTOW from 2,200 to 2,350 pounds. Useful load is best on the standard model (just over 1,000 pounds) and lower on the deluxe Skylark, at approximately 950 pounds. After the tanks are filled, the 175 Skylark has a slightly lower payload than the 172; in the 630-pound range. 

Cessna claims the 175 cruises in the 135–140 mph tas range (117–122 ktas), and with larger tanks than the 172, the 175 can go about 100 miles further nonstop. 

According to book numbers, the 175 also sports much-improved short-field and climb performance, nearly on par with the 182. The 175 Owner’s Manual states the aircraft can climb at 850 fpm at sea level at its full 2,350-pound mtow, while the takeoff ground roll consumes only 735 feet of runway. At lighter weights, climb rate approaches 1,400 fpm, and the 175 needs just 345 feet to get off the ground. 

 

Engine issues

The 175, at least on the surface, offered a great value proposition for buyers. The 1958 and 1959 models of the Cessna 175 sold well: 1,239 left the factory in the first two years of production.

Cessna’s 1959 ads claimed that the 175 could provide “8 cents-per-mile operation,” including fuel, maintenance, storage, insurance and depreciation. 

However, issues with the GO-300 engine soon challenged Cessna’s assertion. Many GO-300s never made it to the promised 1,000-hour TBO, and those that did often required cylinder work to get there.

Steve Ells shares his thoughts on the engine: 

“It’s often thought that the 175 lost favor with buyers because the engine was rumored to be unreliable. The GO-300 initially had a 1,000-hour TBO (amended to 1,200 in 1968), which was not uncommon for that era. One very experienced engine builder described the GO-300 to me as a powerful smooth-running engine, but cylinder problems seemed to head the list of issues. 

One plausible theory is that pilots that had been flying Cessna single-engine airplanes at cruise rpm of 2,350 to 2,500 were very reluctant to cruise at the GO-300’s preferred 3,000 rpm, so they pulled the throttle back to what they thought was the “correct” rpm. 

I believe that if the tachometer had shown propeller rpm instead of crankshaft engine rpm, the engine reputation would not have suffered as much as it did.”

The lower power settings may have “sounded” right to pilots used to standard engines, but at low rpm, the GO-300 didn’t develop sufficient oil pressure to provide lubrication and cooling. 

A 1972 Flying article entitled “Cessna’s Neglected 175” concurred: “People ran the 175s as they would have a 172… the engines warped their valves, broke rings, scored cylinders, cracked pistons. The bad-mouthing began as engines started to fold in 500 hours of a promised 1,000 [hour] TBO.”

Airflow for cooling also likely suffered at low speeds in early tightly-cowled 175s, contributing to premature cylinder issues. Later 175s suffered the opposite problem. The redesigned cowl of the A and later models brought plenty of air to the cylinders. Shock cooling became an issue in low- or idle-power descents.

The Cessna 175’s POH listed cruise speeds and fuel burns down to 36 percent power and 2,400 engine rpm, which may have exacerbated these issues by giving pilots the impression that this was a “safe” power setting.

In addition to the engine problems, the GO-300’s gearbox was prone to issues if operated incorrectly. Numerous posts on today’s Cessna 175 type forums warn pilots to always keep a load on the engine; and under no circumstances to let the propeller “drive” the engine at idle. Gradual, constant-power descents are advised.

 

Declining production

By 1960 and the 175A model, sales had slowed: 540 175As were produced in 1960. Only 225 175B aircraft were sold in 1961.

The 1962 175C model, sporting a Continental GO-300E driving a constant-speed propeller, offered performance and payload improvements. Despite better climb numbers and a greater MTOW of 2,450 pounds, the 175C didn’t sell any better. Only 117 175Cs were produced.

When a 175 isn’t a 175 any longer

In 1963, with a marketing sleight-of-hand, the model that would have been the Cessna 175D morphed into the “Powermatic P172D Skyhawk.” Ostensibly, Cessna calculated that the 172 brand was stronger and the change would help dissociate the airframe from the troubled 175/Skylark name. 

Cessna upped the MTOW to 2,500 pounds, which gave the P172D an impressive 1,100 pounds of useful load. The P172D dropped the fastback fuselage and received the “OmniVision” rear window. It also was fitted with cowl flaps for better engine cooling. 

However, the market didn’t bend. Only 72 of the Powermatics were built; 69 in the United States and three which were assembled under license by Reims Aviation in France as FP172Ds. (The “F” prefix was for “French-produced.”) 

The 175 lives on

Cessna 175 and P172D  production ceased in 1963, after a total production run of 2,118 aircraft. The Skylark was abandoned—almost. 

In addition to the three FP172Ds which had been delivered to European buyers by Reims Aviation, a fourth airframe had been shipped to France.

In mid-1963, Reims engineers converted this airframe into a prototype military liaison aircraft. It featured a 210 hp Continental IO-360-D powerplant matched with a constant-speed propeller.

This proof-of-concept would inspire a number of variants—several of which Cessna eventually certified under the 175 Type Certificate, including the US Air Force T-41B through D (and non-USAF versions, the R172E through J) and the R172K Hawk XP (profiled in the April 2018 issue of Cessna Flyer). 

Cessna produced 2,080 of these IO-360-powered “172s” which were, at least from a certification basis standpoint, 175s.

Though the Reims Rocket is nearly equivalent to the T-41B and shares a common ancestry, it is not included on the 175’s Type Certificate, nor was the French-produced FR172K Hawk XP.

In late 1978, Cessna created a version of the airframe with a retractable undercarriage, a 180 hp Lycoming O-360-F1A6 engine and a three-bladed constant-speed prop. This aircraft, the 172RG Cutlass RG, though a 172 in name, is also on the 175 Type Certificate. 1,191 172RGs were produced between 1980 and 1985.

In total, some 3,271 of these “175 derivatives” left the Cessna factory.

The early positive reception for the 175, the later success of “souped-up 172s” like the R172K Hawk XP, and the number of STC’d 180 hp conversions of legacy 172 airframes demonstrated that there was, and still is, a market for an airplane that is a step up from a standard 172. 

However, the Cessna 175’s reliance on a new, unproven engine to achieve “big-airplane performance” was its ultimate undoing.

As a further testament to the “172-plus” concept and the 175 airframe itself, many of today’s still-flying 175s have been upgraded with one of several STC’d engine conversions. 

Next month: Cessna 175 STCs and modifications, and a flight test of an O-360-powered Skylark.

 

Scott Kinney is a self-described aviation geek (#avgeek), private pilot and instructor (CFI-Sport, AGI). He is associate 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)
Type Certificate Data Sheet No. 3A17 Rev. 46, May 14, 2007; Skylark Associ-ation International Forums, cessna175.org; Flying, Apr. 1958, Jul. 1958, Sep. 1958, Mar. 1959, Jun. 1959, Nov. 1961, Aug. 1972, Sep. 2008. [Note: many back issues of Flying, including all cited here, are available free on Google Books: books.google.com.]
 
SOURCES (PRINT)
“Airlife’s General Aviation: A Guide to Postwar General Aviation Manufacturers and Their Aircraft” 
R.W. Simpson. Shrewsbury (UK): Airlife Publishing, 2000. 
 
“Cessna 172: A Pocket History”
Ron Smith. Stroud (UK): Amberley, 2010. 
 
“Cessna: Wings for the World”
William D. Thompson. Bend, Oregon: Maverick Publications, 1991.
 
“The General Aviation Handbook”
Rod Simpson. Hinckley, Minnesota: Midland, 2005. 
 
Jane’s All the World’s Aircraft 
New York, NY: McGraw-Hill, 1967. 
 
“The Planes of Wichita: The People and the Aircraft of the Air Capital”
Daryl Murphy. Bloomington, Indiana: iUniverse, 2008. 
 
“T-41 Mescalero: The Military Cessna 172” Walt Shiel, Jan Forsgren and Michael R. Little. Lake Linden, Michigan: Slipdown Mountain Publications, 2006.
 
Resources
FURTHER READING
“Cessna’s In-between Single: The R172K Hawk XP” 
by Steve Ells. Cessna Flyer, April 2018.

Available at https://www.cessnaflyer.org/magazines/item/1036-april-2018-cessna-flyer-magazine.html

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Exhaust System 101: Inspection & Maintenance

Exhaust System 101: Inspection & Maintenance

Thin metals and fluctuating temperatures can literally “exhaust” your airplane’s exhaust system. Read on to learn how an aircraft exhaust system is constructed and get several practical tips to identify common trouble spots and prevent unnecessary damage.

Aircraft exhaust systems require detailed inspections and regular maintenance because of the highly corrosive and hot environment in which they operate. Cracks and leaking connections can cause significant amounts of damage to other engine parts, as well as possibly exposing airplane occupants to carbon monoxide. Understanding how to promptly identify exhaust leaks and repair them correctly can help owners and mechanics avoid expensive and/or dangerous problems down the road. (While owners can perform several of the visual inspections outlined in this article, consult your mechanic before performing any disassembly, assembly or repair. —Ed.)

Exhaust system anatomy and construction

Most exhaust risers and mufflers are made of stainless steel or Inconel. (For those who aren’t familiar, Inconel is a trademarked name for a superalloy used in high temperature applications. —Ed.) Some older exhaust systems also contained parts that were made of carbon steel. The pipes and muffler are manufactured with fairly thin walls to help keep the exhaust system as light as possible.

The thin-walled construction and the use of special metals in the construction of the exhaust system can make weld repairs difficult to accomplish in the field. Most items are typically sent to specialty shops that have jigs to prevent warping and have the correct replacement metals and welding rods. 

The single pipes that connect the muffler to each individual cylinder are called risers. A set of pipes that connect each cylinder to the muffler, but which are joined together into one section before reaching the muffler, is referred to as a stack. The outlet from the muffler is the tailpipe. 

Each connection of one exhaust component to another can be accomplished by welding, by use of clamps, or by slip joints. 

Welding creates a strong, but rigid and immovable joint.

Clamped connections utilize clamp halves of various sizes. The clamp halves are connected with nuts and bolts that occasionally corrode over time and require replacement. The clamps can leak and require repositioning or retightening.

Slip joint connections have one pipe inserted a few inches into the adjoining pipe. The mating surfaces fit closely together, but allow for some movement. These connections make the exhaust system removal and installation easier and permit some movement to relieve operating stresses. 

It is important to lubricate all joints using a high-temperature MIL-PRF-907F qualified anti-sieze compound such as Locktite C5-A (up to 1,796 F) or Jet-Lube Nikal (up to 2,600 F).

 

 

Heat and corrosion

The exhaust system’s job is to remove all the hot exhaust gases from each cylinder head exhaust port and deposit them overboard. Exhaust components heat up quickly, but they also cool down rapidly at shutdown. Extreme temperatures and rapid temperature changes create an environment that produces metal fatigue and cracks. 

Connections such as slip joints, cylinder exhaust flange attachments and clamps can all deteriorate and begin to leak over time. Exhaust gas is very corrosive and can do severe damage to any metal component that is exposed to a leaking area. 

 

Muffler inspection

All heat deflectors and muffler shrouds should be removed when inspecting exhaust components. 

Bulges or wrinkles on the muffler are signs of overheating and metal fatigue. The sidewalls and lower sections of mufflers are prone to deteriorate and become thin. Areas where thinning is suspected can be probed with an awl to see if it punches through the material.

A bright light or an inspection camera can be used to check the internal structure of mufflers. Straight tailpipes provide a fairly large opening that allows access for a bright flashlight and inspection mirror. 

Exhaust systems with tailpipes that have bends or that are some distance away from the muffler itself can still be inspected internally by using an inspection camera with a small-diameter, long, flexible shaft.

Broken baffles that are loose in the muffler can be an immediate danger because they can partially cover the exhaust outlet. Jagged or distorted baffles can create hotspots that can cause premature metal fatigue.

 

 

Detecting exhaust leaks

Some exhaust leaks can be found by a visual inspection. Most exhaust leaks leave a gray or black sooty residue around the leaking area. Some leaks leave a yellow-tinted stain on the exhaust system itself. However, not all exhaust leaks leave a stained area behind. 

Some aircraft require substantial pressure test to pass. Always consult the aircraft maintenance manual to ensure that the mufflers are pressure-tested to the required point. Some only need 2-3 psi and some as high as 15 psi.

One of the most thorough ways to inspect an exhaust system for leaks is by use of a shop vacuum, some duct tape and a bottle of soapy water. 

To perform this inspection, the shop vacuum hose is inserted into a cold exhaust tailpipe and thoroughly sealed using tape. The vacuum switch and/or hose attachment on the vacuum should be set to “blow,” so that air blows out the hose rather than being pulled into the vacuum. 

Once the vacuum cleaner is turned on, the air blown in from the vacuum will pressurize the exhaust system enough to check for leaks. Slip joints, clamps and the welds around the muffler itself should all be sprayed with the soapy solution. Leakage will be immediately evident as the soap solution will begin to bubble. 

If it is possible to remove the components from the aircraft, a tank of water can be also be used to check for leaks.

The flange attachments on the cylinders are prone to leaking, especially on the cylinder flange attachments that have only two studs. Most Lycoming engines and a few Continental engines have the two-stud attachment. These flanges are elliptically-shaped, with a hole on each of the small sides. The flange on these connections is inserted over two studs on the cylinder port and drawn up tight with nuts. 

A gasket is used to seal the gap between the flange and the cylinder port. Over time, the flanges can become warped and get bent upward on the ends, leaving a gap in the center, which allows exhaust gas to leak past the gasket. 

Leaks in these areas can be detected by pressurizing the system as described above or by using a small feeler gauge to check for gaps in the gasket’s mating surfaces. 

If the flanges are warped, use of a spiral-wound gasket makes the problem worse. 

 

 

Heat damage and corrosion

As previously mentioned, leaks in exhaust systems should be immediately repaired, not only because of the danger they pose from possible carbon monoxide exposure or fire hazards, but also because the hot corrosive exhaust gas may cause rapid damage to anything that it blows on. This may include components near the exhaust, like the engine mount tubes shown in the picture (top, this page). 

  

 

Cylinder exhaust ports and exhaust flanges

The effects of exhaust heat and corrosion are especially pronounced on the cylinder flange attachments. (Refer to “Detecting exhaust leaks” on Page 30.
—Ed.) The cylinder port attachment for the exhaust flange is aluminum. The flat aluminum surface has two or more threaded inserts with steel studs installed. 

The aluminum degrades and pits quickly when leaking exhaust gaskets allow exhaust gas to blow out between the cylinder head and gasket. The gap and the exhaust leak will get larger with subsequent use if left unchecked. 

If the leak is not addressed, extreme pitting can occur to the point that resurfacing the pitted area on the cylinder is required. This is a laborious repair that involves removing the uneven metal to recreate a flat sealing surface. Surfaces that are severely eroded can’t be fixed and the cylinder must be replaced. 

There is no high-temperature silicone or sealant that will help to seal the gap. Proper sealing requires mating surfaces to be in contact with the exhaust gasket all the way around the gasket seal. Silicone is not effective as a sealing agent because it can’t withstand the extremely high exhaust gas temperatures.

In addition to causing erosion of the cylinder surface, exhaust leaks in the cylinder port area allow cold air to flow directly into the cylinder port through the gap. The cold air in the hot aluminum exhaust port causes the hot aluminum surface to crack. 

These cracks are not usually detectable during a cylinder compression test because they occur in the exhaust port area outside of the exhaust valve. When the exhaust valve is closed, this area is sealed from the combustion chamber. 

There is most likely a crack present in a cylinder exhaust port that has had a leaking exhaust gasket for several hours of operation, whether or not you can see the crack by visually inspecting the cylinder exhaust port. 

The exhaust port is typically covered in hardened exhaust deposits. The only way to remove the deposits is by use of a media blast material—chemical cleaners won’t cut through it—and this requires cylinder removal. 

An untreated gasket leak that causes an exhaust port to crack requires cylinder replacement. Replacing the cylinder is an expensive repair that is preventable by detecting and correcting exhaust leaks quickly.

The flanges on the exhaust risers themselves can be resurfaced by holding them flat on a belt sander and removing the high material until the flange has a perfectly flat surface again. This can only be done if the flange material on the riser is thick enough to allow some removal of the material without weakening the flange. If too much material is removed, the thin flange will become warped quickly and begin leaking again. It may also develop a crack. 

 

Hold-down studs

Leaking exhaust gaskets also corrode the hold-down studs to which the exhaust flange is attached. The threads can become damaged and cause stripped nuts that won’t tighten properly or hold torque. 

The studs also can vibrate and loosen in the threaded cylinder inserts. In this case, an oversize stud or new insert may be needed to hold the stud in place.

 

 

Exhaust gaskets

There are two main types of exhaust gaskets that are used on the cylinder flange attachments. 

The most popular and the longest-lasting are spiral-wound gaskets, also called “no-blo” gaskets. These gaskets are made of a thick carbon steel outer area surrounding an inner sealing area. The seal itself is made of layers of alternating stainless steel and asbestos. Spiral-wound gaskets are less prone to erosion and are more effective than other types of gaskets—provided the mating surfaces on the cylinder and exhaust flange are flat and not pitted. Some mechanics will reuse or reinstall spiral-wound gaskets when they are found to be in good condition.

The other gasket types (sometimes called “blo-proof” gaskets) are thinner and made of stainless steel or copper. These softer and more flexible gaskets are installed in pairs. They don’t last as long in service as spiral-wound gaskets, but they are more pliable and work better to help seal slightly uneven surfaces. The drawback with these coupled gaskets is that they will eventually begin leaking and so must be replaced periodically. In addition, if the exhaust system is removed for any reason, these gaskets may not be reused. 

 

Cracks and slip joint leaks

Leaks due to cracks or excessive leaks around slip joints can only be fixed by removing the parts and having them replaced or repaired. It’s best to send repair work to specialty shops that have the jigs to hold the parts in place as they are welded to prevent deformation. These specialized shops also have the correct repair material, which ensures a long-lasting weld repair. 

Some manufacturers recommend assembling slip joint connections with a small layer of ultra-high temperature anti-seize compound to help ensure a smooth disassembly later on down the road. 

 

Maintenance and operating tips

Here is a list of best practices to help preserve your airplane’s exhaust system.

• Pencils shouldn’t be used to mark exhaust components during maintenance because the graphite can weaken the metal as the exhaust heats up in use and cause a crack.

• Occasionally during an engine runup and magneto check, a pilot may accidentally turn the ignition switch all the way to “off” instead of selecting one magneto. If that happens, the engine starts to die. Most pilots will realize what has happened and will try to suddenly turn the switch back to “on.” This action can cause a severe and potentially damaging after-fire in the exhaust system. If the ignition switch is accidentally shut off during a magneto check, it’s best to let the engine shut down and then restart it. 

• As with all engine components, keeping the engine as cool as possible on climbout and as warm as possible on descent helps to minimize sudden temperature changes and extends the service life of exhaust components.

 

Conclusion

Detailed inspections completed at regular, close intervals can save aircraft owners money in the long run by catching problems before they do too much damage. Basic visual checks of the exhaust system should be a part of every preflight inspection; more detailed inspections should be performed regularly with the help of a qualified mechanic. 

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

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

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