The Duncan Download Blog: Business Aviation Advice & Observations

Innovation Leads to Unique, Quick Trunnion Repairs

Posted by Diane Heiserman on Tue, Jan 23, 2018 @ 08:30 AM

Teamwork, ingenuity, and technical know-how…That’s how Duncan Aviation removes corrosion in the bores of the main landing gear forward trunnions on the bottom side of the wing. We are also the only MRO with the tooling and capabilities to perform this FAA-accepted repair procedure, and we can do it in less than a week.


Lead Machinist Mark Leppky and Master Machinist Todd Hoffman

How It All Began

Nearly 10 years ago, during a scheduled quick-turn airframe inspection, significant corrosion was found in several areas of the aircraft, including the forward trunnion bores. At the time, there were only two options: Clean the corrosion using a standard hone or remove the wing and have it shipped by truck to the OEM for repair in their fixture. The hone method works by cleaning slight surface corrosion but can easily create an oval where a concentric bore is required if you’re trying to remove extensive corrosion. The second option is more precise, but the downtime is sometimes six months or more.

Duncan Aviation’s Machine Shop researched an alternative repair. The team members designed, engineered, and fabricated a fixture in-house to ream the bores. There was just one critical hurdle to overcome: This fixture had to be mounted on the underside of the wing and hold the correct concentricity and axis alignment with no other points of reference but the hole itself. After extensive research and development, Duncan Aviation designed and developed a fixture that met all requirements and successfully removed the corrosion, staying within allowable limits.

Since then, the fixture has been called into service a number of times on other aircraft, all with the same excellent results.

Repairs on the Road

Fixture-assembled-11blog.jpgMost recently, Lead Machinist Mark Leppky and Master Machinist Todd Hoffman took the tooling on the road. The end-customer, an air ambulance operator based in South America, needed the quickest repair possible.

In preparation for the road trip, Mark and Todd inspected the kits, made extra pins, and ensured everything was packed, right down to a cotton swab. On the road, “you don’t have the luxury of walking back to the shop and getting what you need,” says Mark.

They arrived on a Monday and quickly went to work. Through a series of pins, Mark and Todd slowly removed the corrosion by hand, layer by layer, .0325 of an inch at a time. The process requires continual communication and several checks and balances to maintain accuracy. After every cut, the bore’s diameter is checked and the depth measured to make sure it remains square to the back. After the final cut, the bore was within .0002 of tolerance.

“The tolerances are very tight with no room for error,” says Mark. “You get very accurate results following our processes and doing it by hand using sharp tooling, quality fixtures, and being careful.”

The final step is to use the cotton swab to alodine and acid etch the bores before installing a custom- fabricated bushing to bring the bore back to correct diameter. By Friday afternoon, Mark and Todd were packing their kits and getting ready to head home with another successful trunnion repair in the books.

The innovation behind the creation of this wing fixture wasn’t because Duncan Aviation created new technology. It came about because our team members used manual data and regular tooling to conceive of and develop a new method for repair. That resourcefulness and innovation is what sets Duncan Aviation apart. New ideas and test capabilities are developed by taking a different approach to the same information to meet customer needs and change future expectations.


Competitive Advantage: Continuous Improvement

We're not satisfied with standing still. 


Tags: Airframe Maintenance, Learjet, Landing Gear

Duncan Aviation Releases September Duncan Intelligence

Posted by Duncan Download Blog on Wed, Sep 21, 2016 @ 09:00 AM

Have you heard the latest about the FAA's new regulatory requirements for RVSM? How about how WAAS upgrades can impact aircraft sales in Europe?

No? Then you haven't read the September issue of the Duncan Intelligence. 

September Duncan Intelligence


FAA Removes Regulatory Requirements for RVSM Maintenance

In a recent move, the FAA has removed the prerequisite that requires aircraft operators who fly in RVSM airspace to have an FAA-approved RVSM Maintenance program.


TR Added to Bombardier Learjet 20 & 30 Model Series Aircraft Maintenance Checks

The Bombardier Learjet 20 & Learjet 30 series Time Limits and Maintenance Checks have recently added a new Temp Revision to Chapter 5-10-29.


WAAS Upgrades, EASA & Aircraft Sales

If you are planning or may be planning to sell or change an aircraft registration to an EASA-member country, you need to be aware of this.


Top Seven Questions Customers Have About Aircraft Paint

Duncan Aviation Regional Manager shares the most common questions he is asked about aircraft paint.


New Duncan Aviation Test Set Helps Reduce AP Function Test Times

We designed and built a new test set that automates the testing process of the Collins AP 106/107 systems, reducing anticipated function test times.

The Duncan Intelligence is a free, technical newsletter for business aircraft owners and operators. Written in-house by Duncan Aviation's technical representatives, each edition includes technical tips and advice on topics and trends in business aviation. It is a free, monthly e-mail subscription for aviation enthusiasts around the world.

Duncan Intelligence Subscribe Now

Tags: Avionics & Instruments, Airframe Maintenance, WAAS, Learjet, NextGen, Aircraft Paint

1970s: Don Fiedler and the Duncan Aviation Avionics Shop

Posted by Kate Dolan on Thu, Dec 10, 2015 @ 11:14 AM

In 1966, Don Fiedler, who is now the Manager of New Business Development for Components, joined the very young Duncan Aviation avionics team as its fourth employee. Then called American Learjet, the company (Duncan Beechcraft) had recently relocated from Omaha, Nebraska, to the Lincoln Airport, and Don primarily worked avionics, doing repairs and installations in Bonanzas, Barons and King Airs. One Learjet 23 was located on the airport, and he worked on that as well.

Fiedler-desk.gifDon will wrap up his 50th year in the aviation industry—all of which he has spent at Duncan Aviation—with his retirement in September 2016. He has distinctive memories of every one of his five decades, and he fondly remembers the 1970s as a decade in which Duncan Aviation expanded and grew its avionics capabilities. 

“We did some avionics installs on Cessnas and some on helicopters for Harry Barr’s company called Panhandle Aviation,” says Don. “But once Donald [Duncan, the founder of Duncan Aviation] and Bill Lear finished their negotiations in the ’60s, we were one of only five Learjet service centers in the United States, and by 1970, we were doing a lot of avionics work on Learjets, too.”

Thinking of Learjets reminded Don of how much the late Bill Lear loved the hamburgers from the King’s Food Host on 15th & Cornhusker. Although the Lincoln institution was eventually franchised, there were no King’s restaurants in Wichita, Kansas, where Learjet was located.

“Whenever Bill flew a Lear to Lincoln, he’d radio ahead and ask us to have 10 or 15 King’s hamburgers waiting for him. He’d take most of them back to Wichita with him,” says Don, laughing.

After becoming an authorized Learjet service center, Duncan Aviation acquired all of the test equipment and began repairing and installing avionics equipment in Learjets. Donald Duncan was the best Learjet salesman in the country. In his lifetime, Don Fielder remembers that Donald sold more than 450 Learjets.

When an aircraft was in for an avionics installation, Don says Donald could be a bit of a mercenary about getting the work done.

“Donald would say, ‘We’re paying interest on that airplane until it’s sold’,” Don says. “One time, we had a Beechcraft Baron in here that we were selling to King’s Food Host, and we installed a complete avionics package in it, including an autopilot. I worked autopilots in those days, and I had been working on the install and checkout for more than 20 hours. I went home, took a little nap and then kept working. We finally got it working; Larry Collier and I installed it. We tested it at 1 a.m., and it was out the door the next morning!”

DonFiedler4.gifAnother time in the early ‘70s, Don remembers doing an installation on an older DC-3 for Forke Brothers Auctioneers.

“Back then we didn’t have two shifts—we had the day shift and overtime,” says Don. “It was New Year’s Eve, and we were installing new avionics on an older DC-3. It wasn’t going well, but we had to get it done. We stopped briefly at midnight to acknowledge the New Year, but then we just kept on working through the night and into the next morning.”

In 1974, the Avionics shop was split into two departments—the bench and installations. Don managed the five guys who worked the avionics bench, and Ron Hall ran install, which also had about four guys.

Soon after this split, Clay Lacy brought his aircraft to Duncan Aviation for the first time. He’d acquired a really early Learjet 25, and it had a mixture of autopilots, servos and other older avionics equipment that he wanted to modernize.

“The Learjet was a really early serial number, a prototype, and we were modifying it to match the avionics equipment that was routinely installed in new Learjet 25s in the factory,” says Don. “It needed a whole lot of work, though, and it ended up spending six months in Lincoln so we could modify, install and test all of that equipment.

“That was the start of our more than 40-year working relationship with Clay Lacy,” adds Don.

Ron Hall was the Installation Engineer back in those pre-AutoCAD days, and installations sometimes started out as drawings on the back of a napkin.

“Ron knew those Learjet prints backward and forward, and he knew what had to be disconnected or reconnected and to what. The formal drawings were in a big, bound book, but when he was making changes, he’d always make changes on copies of the original prints,” says Don. “Later, he’d go back and render a formal drawing, but he still drew it by hand. Then, we’d add that formal, final drawing to the prints that went with the aircraft.”

In the late 1970s/early 1980s, Larry Collier who was managing the avionics department at the time pushed to get a license for AutoCAD to render avionics prints.

Larry presented his idea to then President Robert Duncan, who agreed. “After that, rendering formal drawings was much easier. Before AutoCAD, Larry or Ron would have to redraw the whole print every time anyone made a change. With the computer program, they just made modifications to the drawing,” Don says.

One of Don’s favorite memories from the 1970s was related to electronics but not necessarily avionics. He remembers the bag phone that Donald Duncan had in his Cadillac. It was one of the first mobile phones anyone at Duncan Aviation had ever seen.

“He loved that phone,” recalls Pam Orr, Travel Coordinator and 39-year Duncan Aviation employee. “When Donald suffered his heart attack and died in 1981, the phone was buried with him.”

2016 is a special year. It is Duncan Aviation’s 60th year of helping business aircraft operators be safe, efficient and productive. For six decades, customers have asked us for solutions and services. We are celebrating our 60 years by telling the stories about the people of Duncan Aviation who listened and took action.

Celebrate with us by subscribing to the Duncan Download blog, following us on Facebook and Twitter (@DuncanAviation) and visiting our anniversary website at

Tags: Avionics Installation, Learjet, 60th Anniversary

Challenger! Learjet! King Air! Oh My! Gear Sets Are Landing at Duncan Aviation

Posted by Diane Heiserman on Thu, Feb 05, 2015 @ 12:16 PM

Landing-gear-shop-fullA near-record number of landing gear sets and components are in-house at Duncan Aviation’s accessories shop in Lincoln, NE.

According to Tony Curtis, landing gear team leader, seven full sets of landing gear and a “whole slew” of individual components, such as struts and oleos, have filled the shop and kept the schedule very busy. All shifts are working tirelessly overhauling or inspecting gear sets and components from Challenger 300, Challenger 604, Challenger 601, Learjet and King Air aircraft.

Although three sets have been completed and already shipped back to operators, Jon Hein, accessories service sales rep, says the workload doesn’t appear to be letting up anytime soon. “Over the next several weeks, many more sets and component parts are scheduled to arrive.”

Because an aircraft can’t go anywhere without its legs, Duncan Aviation has invested heavily in the landing gear customer more than doubling its Accessories shop area, gaining approximately 6,300 square feet of service area, doubling its work benches and adding new tooling and in-house capabilities, including an overhead crane and a new paint booth with curing room.

In 2014, they acquired the capabilities to completely overhaul and repair landing gear for both commercial and business Embraer aircraft. With the necessary technical data, maintenance manuals and aircraft landing gear parts, Duncan Aviation’s Accessories Services has received and successfully overhauled two sets of Embraer gear to comply with the 144-month landing gear restoration.

Take a moment and watch this before and after ERJ-145 overhaul video.



Tags: Parts & Accessories, Learjet, Landing Gear, Challenger

Duncan Aviation Shares Time Lapse Video of Learjet 35 Monument

Posted by Duncan Download Blog on Wed, Dec 17, 2014 @ 09:36 AM

Head down the main entrance drive of Duncan Aviation’s Lincoln, Nebraska, facility and you’ll see a Learjet 35 set atop a 20-foot stand, slightly tilted, as if frozen in time during takeoff.


The company jet flew for nearly 13,000 hours and boasted more than 10,000 landings at the time of its retirement in 2009. Though Duncan Aviation team members sold the aircraft’s engines and all salvageable parts, they kept the shell of the aircraft intact for years before it made its shift to sculpture along the main entrance drive of Duncan Aviation’s Lincoln, Nebraska, facility.

During the past five months, team members wrote messages inside the retired company jet, creating a unique time capsule that captured the experiences of anyone who piloted, flew in, worked on, purchased and delivered parts for, cleaned, fueled and towed this piece of Duncan Aviation history.

Though the Learjet was added to the campus late this year, plans for the monument began nearly four years ago. With a lot research, planning and modification of the aircraft, a piece of Duncan Aviation’s early days now sits across from the newly opened 175,000-square-foot maintenance hangars.

To view the time capsule’s interior, newly painted exterior and progression from hangar storage to three-prong stand, view the following time lapse video.

View Learjet 35  Time-Lapse Video

Tags: Announcements, Learjet

Duncan Aviation Permanently Displays Retired Learjet 35 Time Capsule

Posted by Duncan Download Blog on Thu, Oct 30, 2014 @ 01:34 PM

Nearly four decades ago, Duncan Aviation bought its first Learjet 35. Today, the retired jet made the shift to sculpture as it was placed on permanent display along the main entrance drive of Duncan Aviation’s Lincoln, Nebraska, facility.

In 1976, this Learjet 35 allowed a person to reach places and carry more than any other prior business jet could achieve. Now, those parts and components have been sold and all that’s left of the Lear is a shell.

During the past five months, team members wrote messages inside the Learjet, creating a unique time capsule that captured the experiences of anyone who piloted, flew in, worked on, purchased and delivered parts for, cleaned, fueled and towed this piece of Duncan Aviation history.


Tags: Announcements, Learjet

Learjet: Common Exchanged Parts

Posted by Diane Heiserman on Tue, Oct 29, 2013 @ 07:00 AM

Contributed by Larry Stewart, rotable manager

Duncan Aviation has built and maintained one of the largest business aircraft parts inventory in the industry. Our team of aviation professionals has the experience, contacts and connections to identify and secure some of the hardest to find business aircraft parts.

Because of our long history and experience with the Learjet aircraft, we know the most commonly exchanged parts and keep an inventory available to meet customer needs.

Below are some of the more commonly exchanged life-limited parts on a Learjet airframe that have been known to not make the next Time Before Overhaul (TBO).

stab actuator

Stab Actuator 2332540-214

The stab actuator adjusts the horizontal stabilizer to provide longitudinal trim. The actuator comes due for overhaul every 600 hours. Failures that sometimes occur are unit trips autopilot off line, & no manual trim.

Modulating Valve 6600202-1

Modulating Valve 6600202-1, -3

The modulating valve regulates the mixing of bleed air to control temperature. If it becomes stuck open or closed, aircraft cabin temperatures can become uncomfortable. The value is spring-loaded and sometimes fails to compress on run-up. It is not uncommon for these valves to leak over time.

Hydraulic Pump 6600301-3

Hydraulic Pump 6600301-3

The hydraulic pump controls the flow of hydraulic fluid through the system. Hydraulic fluid leaking at the drive shaft is a symptom of the nose seal failing to make a proper seal.

Static Inverter 6608109-3

Static Inverter 6608109-3

The static inverter powers all onboard instruments that need aircraft power. Failures include unit being intermittent, pops breaker, and low or no output.

NWS Servo 6608278-2

NWS Servo 6608278-2

The nose wheel steering servo controls the rate of turn while aircraft is being taxied. Common failures are time change, pops breaker, low torque and pulls to the right or left.

Parts & Exchanges

 Duncan Aviation is constantly adding to its inventory to ensure customers have a true one-stop shop when it comes to acquiring parts or exchange units. Search our on-line inventory for aircraft parts and inventoryavailability or chat live with a Parts & Rotables Sales Rep. Our international business aircraft components solutions experts are available 24/7/365 and can handle any business aircraft system problem with immediate parts exchanges.

Larry Stewart is a Rotable Inventory Manager located at Duncan Aviation’s Lincoln, Nebraska, facility. He specializes in the Learjet and Citation airframes. His aviation career began in 1973. 

Tags: Parts & Accessories, Aircraft Parts, Learjet

Duncan Aviation Receives Award for the Second Consecutive Year

Posted by Diane Heiserman on Wed, Oct 23, 2013 @ 07:00 PM

Contributed by Kaela Paseka, graphic design lead

Bombardier ASF Award 2013(2)

L to R: Bombardier Aerospace Vice President, Aircraft Service Centers, Stan Younger, Duncan Aviation’s John Biever, Aaron Hilkemann, Rod Christensen—Manager Airframe Service and Bombardier’s Director, Authorized Service Facilities, Chris Milligan.

On Wednesday during the National Business Aviation Association (NBAA) Meeting and Convention in Las Vegas, Nevada, Duncan Aviation was again recognized by Bombardier as a top authorized service facility for its support of Bombardier customers. Judged on a set of criteria that included quality, compliance, customer satisfaction and customer influence, Duncan Aviation’s Battle Creek, MI, facility was named the winner of the North America category of the 2013 Bombardier Authorized Service Facility Excellence Awards.

Bombardier Aerospace Vice President, Aircraft Service Centers, Stan Younger spoke to the award winners at a private ceremony at NBAA. “It is our ASFs attention to quality and their dedication in providing customers world-class service and support that is being recognized today. Each winner demonstrates a commitment to putting customers first,” said Younger.  

Duncan Aviation President Aaron Hilkemann and John Biever, Vice President Airframe Services in Battle Creek, Michigan, accepted the award from Stan Younger and Chris Milligan, Director, Authorized Service Facilities for Bombardier.

“We enjoy representing Bombardier and their products in supporting of our mutual customers. It is a great mutually beneficial partnership that has worked for many years,” says John Biever.

More than 30 Duncan Aviation representatives are attending NBAA this year, representing several Duncan Aviation services, including airframe and engine servicespaint and interior modificationsavionics and parts support and aircraft sales and acquisitions.

Stop by the Duncan Aviation NBAA booth #C8543 to congratulate Aaron, John and the rest of the Duncan Aviation team.

Kaela Paseka is Duncan Aviation's Marketing Graphic Design Lead, and is currently attending NBAA 2013 at Duncan Aviation booth #C8543. She began her career in aviation in 2006.

Tags: Conventions & Exhibitions, Announcements, Learjet, Challenger

Learjet 60: New Brake Airworthy Directive

Posted by Diane Heiserman on Fri, Aug 16, 2013 @ 01:43 PM

Submitted by Dave Schiver, Airframe Tech Rep

Learjet 60 Airworthiness Directive

AD2013-13-09 is issued to prevent failure of the braking system or adverse operation of the spoiler and thrust reverser system due to external damage.

The Federal Aviation Administration (FAA) has issued Airworthiness Directive AD2013-13-09 in regards to the Learjet 60 Brake System. This AD requires three separate Service Bulletins (SB) be accomplished within 12 months or 600 hours from August 6, 2013, the effective date of the AD.

The following are the required SB:

SB 60-32-33, Dated July 23, 2012

Installation of rigid hydraulic tube assemblies and improved MLG squat switch bracket

SB 60-57-7, Dated July 23, 2012

Installation of metal shields and brackets for the wiring and tubes on the lower struts

SB 60-78-7, Dated May 1, 2006

Improved wheel speed detect box and TR interface box

The summary and complete AD can be viewed at the following:$FILE/2013-13-09.pdf

Dave Schiver is an Airframe Technical Representative at Duncan Aviation’s Lincoln, Nebr. (LNK) facility. He specializes in Learjet aircraft. His aviation career began in 1981.

Tags: Regulations, Airframe Maintenance, Learjet

Learjet 35/55: Prevent Premature Starter Armature Failures

Posted by Diane Heiserman on Tue, Jul 02, 2013 @ 07:00 AM

Contributed by Jerry Cable, Accessories Tech Rep

Learjet/Bendix Starter 6608268-6

Our experience has taught us that a commutator and brush reconditioning program will extend the life of your armature and brushes.

Technicians in the Duncan Aviation Accessories shop, recommend a reconditioning program for the Lear/Bendix starter 6608268-6 on Learjet 35/55 aircraft. The reconditioning of the armature commutator and re-seating and re-run on the brushes every 800 hours (maximum) will divert armature commutator damage.

In cases where the armature commutator and brushes are not reconditioned, the commutator will become pitted and burnt from the diminishing electrical connection to the eroded brushes. This armature commutator damage will progress to the point of mica electrical breakdown (mica is an electrical insulation between the armature commutator bars). This mica breakdown is non-reversible in most cases, and the armature must be replaced.

A common symptom that this is occurring would be the engine is slow to spool at engine start.

Accessory Service Expansion

Scheduled to open later this summer, Duncan Aviation will open its newly refurbished Accessories Shop in Lincoln, Nebraska, that will more than double the footprint of its service area. The Accessory department will gain approximately 6,300 square feet of service area, double its work benches and add new tooling and in-house capabilities, including an overhead crane and a new paint booth with curing room.

To read more about the Accessory department expansion and added tooling, read the Spring 2013 Duncan Debrief.

These expansions come in response to customer requests and changing customer needs. As the industry continues to shift toward larger business aircraft, a trend fueled by technological advances and increased globalization, Duncan Aviation’s new expanded shop areas will be able to accommodate the volume of maintenance, modifications and completions work our customers require.

Jerry Cable is an Accessories Tech Rep located at Duncan Aviation’s Lincoln, Nebr., facility. He is a landing gear and accessory components and systems specialist. His aviation career began in 1991.

Tags: Parts & Accessories, Squawk Solution, Learjet, Maintenance Event Planning


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