Top Three Causes of Aircraft Build Errors and How to Avoid Them

By Lisa Turner, EAA 509911

This story first ran in the May 2019 issue of EAA Sport Aviation.

Rick walked around the aircraft, admiring the craftsmanship and beauty of the two-place tube and fabric kit airplane.

“It’s beautiful, Ted. How long did it take?”

“About four years. I brought it out to the field last week, and I’ll be
ready for my test flight this weekend.”

“Who is your flight advisor?”

“I wanted to build it completely by myself. No help.”

“I can understand that, but a technical counselor and flight advisor
don’t help you build as much as help you do it right and not miss anything. Did
your designated airworthiness representative find any issues?”

“He didn’t look much at the airplane,” Ted said. “He just looked at my
build log and pictures.”

Rick sighed. “Well, I shouldn’t be telling you what to do, but I’d
definitely have someone who knows the airplane look it over carefully before
your flight.”

“Thanks, Rick. I’ll be fine.”

The FBO porch-sitting clique was settled in with their mugs of coffee
Saturday morning as they heard the airplane leave the ramp nearby and start
some high-speed taxi runs.

“Isn’t that Ted in his new experimental?” an onlooker said.

“Yes,” Rick said. “I think he’s about to make his first flight, and I’m

The beautiful red and white taildragger lined up on Runway 15 and
gathered speed. As it rotated, it went nose up at 5 feet off the asphalt. The
onlookers gasped as the airplane slammed back down onto the runway tail first.
Then the nose came down, and the airplane bounced forward, propelled by the
momentum. Incredibly, they saw the airplane taxi off the runway seemingly

Rick and two others ran out to the airplane.

“Are you okay?” Rick asked Ted.

“I’m okay,” Ted said, shaking. “Wow, I don’t know what happened.”

“Well, you’ve got bent gear. Let’s pull it back to the hangar.”

In the hangar, Rick pulled the operating limitations and weight and
balance sheet out of the airplane side pocket.

“Ted, this isn’t right. Looks like you are really tail heavy.”

“I put 20 pounds in the tail because I thought it was nose heavy.
Shouldn’t it balance in the middle? It was confusing.”

“Where’s the datum?”

“The what?”

Rick shook his head. “Will you get a flight advisor, please?”


This story is based on a real
event, but the names have been changed

It’s taken some time to sort out statistics on homebuilt aircraft
accidents in the 67 years since “experimental amateur-built,” or E-AB, got its
own category. Because many E-AB accidents are not reported (not rising to the
level of an NTSB investigation), it’s difficult to develop an accurate picture.
EAA, working with the FAA and NTSB, has tracked accidents for many years, but
we still don’t have the data we need when it comes to accidents early in the
life of an experimental aircraft. Digging into the details to determine the top
causes of these accidents has been difficult.

One well-known aviation writer, Ron Wanttaja, EAA 275698, decided to
dig into aviation accident detail several years ago. Recently, he wrote about
first flight accidents, suggesting that build error is a major cause. After
reading his thorough analysis, I surmised that adding informal data from technical
counselor (TC) and flight advisor (FA) experience might give us more clues
regarding build errors and help us prevent them.

Every time that a homebuilder has a “close call” and discovers a build
error, and every time that a homebuilder has an unreported accident where they
drag the machine back into the hangar only to discover a build error, we have
unreported data. This is valuable information that EAA chapters, TCs, and FAs
have anecdotally that we’ve been asked to not talk about, lest we embarrass someone.

So, I’m using all of the data collectively (and anonymously) to write
about what I think are the three top build error causes, and how to avoid them.
There’s good news in the mix as well. Experimental aircraft accidents of all
types are actually going down, even as the fleet size increases. So, we’re
headed in the right direction. Still, Ron reports that about one in every 130
new homebuilts suffers a reportable
accident on its first flight.

As you might expect, operational problems become evident right away,
usually during taxi testing and the first flight, and then later right after
the 40-hour mark. Not surprisingly, the top three problems during the first 100
hours are fuel and carburetor issues, controls and weight and balance issues,
and engine installation and associated system (fuel, oil, air, prop) failures.
These problems lead primarily to loss of control and engine failures, according
to the NTSB.

Not Enough Training or Knowledge

Examples include missing building skills and lack of technique. They
include not using correct procedures when working with materials and not
developing the kinesthetic skills required for mechanical tasks, such as torquing
a bolt or safety wiring. This also includes not “seeing” crossed controls; a missing
safety wire; or wrong, loose, or missing hardware.

How do we know? Last year I wrote an article about a psychological
affliction called the Dunning-Kruger effect. What it means is that we may not
recognize when we need help. We don’t know what we don’t know. Any tools to
help us “calibrate” our own ability and knowledge will be useful, but only if
we are open to them.

How to avoid problems:

  • Be open-minded. Is this your first aircraft project? Be careful if you’ve worked on cars, trucks, building construction, etc. You may be highly skilled in these trades, but all that means is that you are endowed with aptitude. This is a great beginning to an aircraft project, but be wary if you think you don’t need any additional skills or knowledge.
  • Even if this is a second or third aircraft, take an inventory of what you need to know for the next one. For example, I went from composite to fabric, and I knew nothing about fabric. I went to a SportAir Workshop, and I realized that if I had not gone, I would have wasted a lot of time learning on my own.
  • Engage a TC and an FA. Even if you consider yourself to be advanced, an extra pair of eyes from someone highly knowledgeable and as passionate about building as you are will improve the quality and safety of your work. It’s free.

Not Understanding and Following All of the Instructions

Examples include using the wrong hardware, using the wrong filler,
using the wrong type or gauge of electrical wire, adding structural components
not run through an engineering review, using a nylon lock nut where a castle
nut should be, etc.

You may feel that since you’re building an experimental aircraft, you
can do anything you want. You can certainly do anything you want, but unless
this is one of many aircraft you’ve built, and you’ve checked the changes out
with the kit manufacturer, it will be much safer if you follow the
manufacturer’s instructions.

How to avoid problems:

  • Study the instructions and directions. Make up your schedule for the build, and determine approximately what you’ll accomplish in that time frame. I like to make a copy of the directions and mark them up with questions before beginning. This way you’ll have fewer surprises and stoppages.
  • Engage a TC. We already talked about this. Did I mention it’s free?
  • If your kit manufacturer doesn’t have a pilot’s operating handbook template, now is the time to make your own (see Airworthy in the February 2018 issue of EAA Sport Aviation for tips). A future owner of your aircraft will thank you.
  • If you want to make changes to the design, get advice from the kit manufacturer or from an engineer. Many of the loss of control accidents on first flights were due to extra experimentation that was not thought all the way through. Don’t get me wrong — there’s nothing bad about experimenting, but realize that it carries risk. If you are doing your own design, test it thoroughly on paper before a first flight.

Inadequate Flight Testing

Examples include engine system hookup errors, not calibrating engine
information systems, fuel system switch and routing mistakes, inadequate taxi
testing, not using the correct hardware or materials on control systems, and
not having a first flight plan of action, including a safety review.

Like Ted in the story that began this article, you may feel that you
can do whatever you want when it comes to testing your aircraft. And you
certainly can. But wouldn’t you rather have the highest safety margin possible
so that any surprises you do encounter are manageable?

Most of the builders that I’ve helped have welcomed the scrutiny.
Homebuilders are a dedicated and knowledgeable group. I have not met any
builders who were purposefully sloppy or arrogant. They usually say, “Wow, I
never saw that.” Once again, the more eyes you can get on your airplane the

Screen Capture by Snagit

The quality and completeness of the test programs from the kit
manufacturers are all over the map. Many builders do not realize how critical
of a phase this is and do the minimum. If the airplane flies nicely, then
that’s it. Most E-AB accidents are either in the first hour — the first flight
— or after the signoff when the pilot decides everything is fine and stops
inspecting and testing.

How to avoid problems:

  • Should you be doing your own first flight? Don’t let your ego get in the way.
  • TCs and FAs have known for a long time that many of the flight testing programs that homebuilders use are inadequate. The excitement of that first flight seems to wash out the good intentions to stay disciplined in testing. A first step to correcting this is to use an FA.
  • Don’t count on a designated airworthiness representative to find problems. Good DARs will probe, and perhaps find things that surprise you. But this pre-work is your responsibility.

When we add the soft data from DAR, TC, and FA anecdotal reporting from
the field, we arrive at a picture of builders wanting to get it right but
sometimes not knowing how. With all the resources available to builders and
used E-AB owners, we should be able to drive the accident rate down even

The introduction of the EAA
Flight Test Manual
to a previously loose and haphazard testing phase, and
the phase in which most of the accidents occur, is revolutionary. I expect that
all technical counselors and flight advisors are breathing a sigh of relief, as
are DARs. Adding an additional layer of safety to one of the most wonderful
endeavors we can undertake in life is good.

Lisa Turner, EAA 509911, is a manufacturing engineer, A&P, technical counselor, flight advisor, and former designated airworthiness representative. She built and flew a Pulsar XP and Kolb Mark III, and is currently restoring a Waco UPF-7 with her husband. Lisa is a member of the EAA Homebuilt Aircraft Council and Women in Aviation International. For more from Lisa, read her Airworthy column each month in EAA Sport Aviation.

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