A Cautionary Tale: Forced Landing After Engine Overhaul

by HPA · October 25, 2017

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A Cautionary Tale: Forced Landing After Engine Overhaul

This is the story of an aircraft incident – not an accident. An accident, according the NTSB definition, is a flight operation in which “any person suffers death or serious injury, or in which the aircraft receives substantial damage.” So technically, if you (and your passengers) walk away uninjured from a forced landing after an engine failure, the amount of damage sustained determines whether the NTSB considers this an accident. The blown engine, or any of the scrapes, bends, dings and dents incurred after touchdown may not be enough to “upgrade” the incident to an accident.

Hopefully, knowing in advance that this story has a happy ending won’t lessen the impact of its lessons. As with most of these stories, there is a chain of smaller causal events to be followed that ultimately caused the larger incident – like tracing the Nile back to its source, or a hurricane back to a butterfly fluttering its wings. So, sit right back and you’ll hear a tale…

The Butterfly Flutters…

A colleague of mine (let’s call him Keith) owns a retractable Cessna 182, and he uses it in his aeronautical consulting business. One blustery winter day in February, he flew the plane to an uncontrolled field in eastern North Carolina with a passenger on board. The strong, variable winds were not favorable that day for the single runway, and Keith knew that he would need to use his best crosswind technique to cope. “I was focused on getting the plane on the runway, but honestly, never considered that I needed to keep flying after the wheels were down,” said Keith. On rollout, the adverse winds were strong enough to lift the tail of the aircraft, causing the two-bladed prop to slightly impact the tarmac.

Lessons? For starters, Keith admits that maybe he shouldn’t have flown at all that day, knowing that the winds at the destination were so unfavorable. Further, the C182 tends to be a bit nose-heavy, and the W&B that day with two passengers up front and none in the rear might have exacerbated that tendency. Couple that with a strong gusty wind that may have momentarily turned to a quartering tailwind and – prop strike. “Maybe if I kept more back pressure on the rollout, it might have made a difference,” Keith laments.

Generally, aircraft engines that experience a sudden drop in RPM due to prop strikes require a mandatory disassembly and inspection of all rotating engine components. Consequently, Keith did not fly his aircraft home that day; he called his insurance company and started the process of looking for a shop to inspect his engine.

The Overhaul from Hell

As part of his business, Keith often attends aircraft industry trade shows; AirVenture (Oshkosh), NBAA, etc. At one such show, he visited the booth of an engine overhaul business (“Acme”), was impressed by their promises of rapid turn-around, and filed them away mentally. After the prop strike, Keith contacted Acme to get a quote for the mandatory inspection and further inquired as to what it would cost to upgrade the inspection to an overhaul. “I was getting close to TBO anyway; this looked like a golden opportunity,” says Keith. It was, because the insurance company was already obliged to cover the costs of engine removal and installation. Acme was signed on for the work, and the engine was removed and shipped to their shop.

As the promised time for the completion of the overhaul neared, Keith began to anticipate the day he could fly his plane back home. (I know, because my calendar had a series of cancelled appointments to fly him to North Carolina in my aircraft.) Keith kept getting positive status reports from Acme about the overhaul progress, only to be disappointed by the next report. The Acme manager Keith dealt with apparently couldn’t be trusted to tell him what was really going on, and Keith had no idea why. Financial problems? Personnel issues? Keith said at the time, “I believe (he) is a very poor manager and has no idea when things will get done, yet he promises yesterday. Worse – I realized this week that he flat out lies.” The engine was eventually delivered back to North Carolina, 3 months later than promised.

Every good story has an interesting character or two. This story has “Luther”, the good ol’ boy mechanic at the airport where Keith had the prop strike. Pilots who have used Luther in the past have described him as competent and knowledgeable, but loquacious. Now that the engine was back, Keith was calling Luther for status updates on the installation, and getting more than he bargained for. From an email I found, Keith wrote, “He’s been talking for 30:25 now. I’m not sure he’s winding down yet. Good grief.” Clearly, Keith sent the email while Luther was still talking his ear off.

Keith was finally able to fly the plane back home, but the troubles with Acme continued. Another email from Keith, “It appears the carburetor has to go back to Acme. Check valve is bad and It’s leaking. The overhaul from hell continues…”

“I’m not going to make it.”

The carburetor issue kept the plane on the ground for a while, but the C182 was airworthy again in October, and Keith was itching to fly. What ensued is best described in Keith’s own words:

Today was a fantastically beautiful day… Clear skies, light winds, and 65 degrees. I went to the airport at around 1:30 to check the plane, clean up the hangar, fuel the plane, and do a short flight to make sure all is ok before flying to the Boston, MA area… After fueling the plane, doing the remaining preflight checks, I took off, enjoying the early stages of fall colors. I reduced power to the top of the green arc on manifold pressure going through 800 feet and flew north. At 1300 feet I made a roughly 90-degree left turn…toward (a nearby airport) to do a landing, then return. I started to reduce the RPMs for a slow cruise. The engine began to run a bit rough. As a result, I turned back toward (my home airport). The engine got rougher as the seconds ticked by. I made a radio call… saying ‘Nxxxx is returning to the airport, engine is running rough, this is not practice.’ I receive two replies saying they were going to get out of the pattern and the airport was mine. A few seconds later the cockpit was filled with smoke and the engine was silent. After decelerating to best glide speed and shortening the range to possible landing sites I was assessing, my next radio call was, ‘I’m not going to make it.’ By the time that call was made I was at 800 feet. The airport was not an option and I had selected a road in the back of an industrial park, the last few blocks of which had no buildings. It was clear that making the road was in question. … I kept the flaps and gear up until I was sure I had the road made. That was quite low. I put the gear handle down and lined up on the road (missed the yellow line by around 4 feet). Alas, the main gear locked, but the nose gear did not. Shortly after the nose wheel touched it collapsed… The plane slid to a stop on the road. I was fine.

Next radio call I heard was ‘good job buddy’ from one of the pilots that had cleared the airport, then some chatter about where I was and that it appeared I should be ok. I called to say I was. For the next four hours, I stayed away from the media trucks with some help from the police. I talked to (local) Police, Fire Department, and Rescue. I also talked to State Police, a few people at the FAA, and the insurance company. What a day.

The training worked. My only real question about options is: If I had put the gear down a few seconds sooner would the nose wheel have locked and would I have still made the road? I walked away, that’s a blessing. It’s also a blessing that I was alone.

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Aftermath

Of course, the most interesting lessons here involve the post-mortem inspection of the blown engine. There were only 52 hours on the engine since its overhaul when it failed. The aircraft had a fresh annual. What happened?

The culprit was the cylinder #1 connecting rod, which became disconnected from the crank when a bolt sheared, punching a couple of holes in the crankcase in the process. Keith’s recorded engine monitor temperatures confirm this, but also mysteriously showed cylinder #4 stopped firing first. There was no explanation for this.

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Surprisingly, no smoking gun was found in the analysis to prove that the “overhaul from hell” was directly responsible. Acme was indeed experiencing some financial trouble during this period, but there is no evidence that they used non-PMA approved parts to cut costs. The connecting rod attachment point uses “stretch” bolts, a type of engine bolt that is purposely torqued until it deforms to maintain its clamping force. Because they deform, the bolts can’t be re-used. Improperly torqued stretch bolts may deform to the point of inviting premature failure, but this is hard to prove. There is at least circumstantial evidence that the working conditions at Acme during this period were not conducive to performing the highest-quality work.

Whatever the cause, the lesson is that infant mortality for ANY engine; new or reconditioned, is a real thing. Infant mortality is a reliability engineering term that refers to the early failure rate of some products, as illustrated by the “bathtub curve” shown below. In the early life of products adhering to this hazard function (and aircraft engines do), the failure rate is higher than normal, but rapidly decreases as early sources of potential failure – defective parts and installation errors, for instance – are surmounted. Keith’s engine failure occurred at the back end of this curve; most of these types of engine failures happen during the first dozen hours or so. To stack the odds in their favor, pilots should follow the break-in instructions for engines meticulously, remain vigilant for any warning signs, and stay close to airports during the break-in period.

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Figure 1 The ‘bathtub curve’ hazard function (blue, upper solid line) is a combination of a decreasing hazard of early failure (red dotted line) and an increasing hazard of wear-out failure (yellow dotted line), plus some constant hazard of random failure (green)

 

Believe it or not, to repair the engine Keith went back to Acme, recently re-organized as the “New Acme”, minus some the former employees Keith had dealt with. The repaired engine was installed in February, a full year after the original prop strike occurred. A new, shorter three-bladed prop replaced the old two-blade. Keith was flying within a few weeks, and has put hundreds of hours on the engine since, without incident.

“Good job, buddy.”

Paul Volk is a pilot, engineer and aviation enthusiast with over 4200 hours of flying time. His experience in avionics development and avionics-related research has been at the vanguard of technologies such as ADS-B, cockpit-based decision aids and FAA NextGen capabilities that will affect the future of general aviation.

How it Started

One of my best friends in high school, (Doug Gray) was a private pilot. He offered to take me up for a flight in a 1967 Cessna 150, N6228S. We took off from Calhoun, Georgia, and he took me on a scenic tour of the area, I was hooked. I later found out that my English teacher, (Jan Haluska) was also a flight instructor and the school was offering a ground school course the next year, which he taught, along with flight training with the goal of becoming a private pilot. I managed to talk my dad into funding the training, at the time the total cost was right around $500. Cessna 150 rental rates where $12 an hour, and the 172 we used for cross country was $15 an hour including fuel.

Training Begins

It started August of 1977. The fall semester rolls around, and I am enrolled in ground school, and if memory serves me, we met twice a week. First came the paperwork for my student pilot certificate, which at the time was included with the 3rd class medical. I loved ground school, especially learning navigation, plotting courses on the sectional, again this was before iPads and GPS, so we did a lot of dead reckoning and VOR navigation for cross countries. At the end of the course, I made an 83% on the Private Pilot written exam, remember this was before we had the question-and-answer books that on future test I would consume before taking a written.

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Flying

The fun really began on August 22, 1977, it was my first flight. To my surprise we used the same Cessna 150, N6228S that my friend Doug Gray had taken me for a ride in. The Cessna 150 had a standard VFR instrument panel, with one NAV/COM, and one VOR CDI. No intercom, so no headset, at the time I didn’t know what I was missing. I didn’t get my first headset until I started my instrument training in 2003. I was a big guy, I was 6’ 4” and weighed 245 lbs. but I do not remember being uncomfortable in the 150 even with the instructor in the right seat.

First flight lasted .8 hours, and we accomplished orentation, shallow turns, stability, and effects of flight controls. Over the next few months we added steep 720’s, slow flight, stalls, turns around a point, S-turns, emergencies, landings, (short field, soft field and normal).

Learning

At this point I want to talk about a training experience that still stands out. We were close to solo and were practicing takeoffs and landings. Turning base to final Jan got very upset at the way I was cross controlling the aircraft. Cross control is when you are in, say a left turn, and use opposite rudder to line the nose up with the runway. So, he had me depart the pattern and head east to the practice area, and climbing up to 5500 feet MSL, he had me slow down to just above stalling speed, start a left shallow turn and add right rudder. As the airplane stalled I had the strangest sensation, no roller coaster has ever come close, instead of blue sky in the windscreen I was looking at brown ground, and as far as I could tell we were upside down, through the terror of the moment Jan talked me out of the spin, controls neutral, oposite rudder, pull slowly out of the dive. As we leveled off he asked me what altitude we were at, as I remember it was around 2,800 feet MSL. Then he asked me what would happen if I experenced this on base to final in the traffic pattern. The answer was obvious, I would be a pile of wreckage off the end of the runway with a very short-lived aviation career. Needless to say this cured my cross-control tendencies.

Another training event the sticks out in my mind was the first time we did takeoffs and landings at the High School runway. The runway was 1,500 feet long, not sure of the width, but it seems like we had about 5 feet on each side of the wheels when on the center line of the runway. Landing from the south you also had to go between a cutout in the trees to be able to stop in time on the runway. After getting confortable landing here every runway since seemed huge. I remember landing at Chattanooga (KCHA) on a night cross country and commenting to Jan, that I felt like I could of landed sideways on the runway, it felt that large.

Very soon after this I started wearing old shirts to all my flight lessons, the reason for this occurred on February 8, 1978. The lesson that day was stalls, takeoffs and Landing. As we were taxing back in Jan told me it was time for my first solo. I was very excited, and after some last minute advice from Jan, including watch for floating on landing the plane will be light with him not in the right seat, complete 3 takeoffs and landings to a full stop. It was a blast, and at the end of my shirt was shorter in the back because Jan cut the tail out of it signed and dated my solo [an aviation tradition]. Total flight time accumulated on the day of my solo was 18.1 hours. I was now officially a pilot with solo priveleges.

In my next article I start cross country training, when Jan decided that it would be best accomplished this in the 172. Checking out in N5970R was like moving into a 747, this started a love affair with one of my faviriote planes to date. Since this time I have flown over 900 hours in many different models of the 172 and feel like I am stepping into an old friend every time.

More about Randy here: https://www.flyhpa.com/team/randy-delong/

 

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