The Duncan Download Blog: Business Aviation Advice & Observations

By Kevin Miesbach, Shop Manager-Avionics/Instruments

On Monday, June 3, Duncan Aviation consolidated its Shipping and Receiving operations with all shipments to Duncan Aviation-Lincoln now going to one new centralized receiving location. This move improves the efficiency of how packages are received and moved about the company, resulting in many customer benefits.

Consolidated Shipping Services

Customers will no longer have to ship their accessory or avionics units to different physical addresses at the Lincoln Airport to reach the Duncan Aviation shop performing the work or needing the parts. That means whether customers are shipping an accessory item for repair or overhaul, an avionics unit for repair or overhaul, or sending Duncan Aviation an inventory of parts for consignment, they will be able to use the same address.

FedEx Zip Code –68500

As part of consolidation, Duncan Aviation has obtained a special zip code for use in the FedEx shipping system. All packages addressed to this zip code are delivered by FedEx to Duncan Aviation’s Lincoln facility first thing in the morning.

When sending units to Duncan Aviation via FedEx, please use the following address and zip code:

Duncan Aviation, Inc.
Shipping and Receiving
4001 N Park Rd
Lincoln, NE  68500

Reduced Turntimes

The consolidated shipping, along with radio frequency scanning technology implemented in Duncan Aviation’s package receiving process, allows for more efficient shipment receiving and dissemination. Units make their way from the receiving dock to the repair shop and ultimately the workbench even quicker than before and are able to see real-time when an expected unit is received into the system. And customer paperwork is electronically attached to the work order for a more efficient process all-around. We look forward to our customers experiencing the financial and turntime benefits of the new receiving procedures.

No AOG Shipping Charges

All Duncan Aviation customers who need AOG services and use the special FedEx zip code of 68500 no longer need to mark and pay for the “EARLY AM” service from FedEx. Technicians have already been reporting AOG units arriving earlier than the previous “EARLY AM” shipments.

Other Carrier Shipping

When sending units to Duncan Aviation via any other shipping carrier, please use the following address and zip code:

For the most efficient service, it is best to use the shipping addresses as outlined above. However, we have been assured by our carriers that if you forget and use the old addresses, shipments will still make it to Duncan Aviation and the proper shops.

Duncan Aviation's Component Solutions offers extensive aircraft parts repair and overhaul services—including loaners and exchanges—for avionics, instruments, parts and accessories, at the same time maintaining a large inventory of aircraft parts for sale. Their streamlined services and competitive turntimes satisfy hundreds of requests throughout the world 24 hours a day, 7 seven days a week.

Duncan Aviation is on schedule to complete the largest expansion project of its Lincoln, Nebraska, location. When complete, two new 40,000-square-foot maintenance hangars will be able to accommodate the larger body business aircraft that many customers are currently operating. And additional 95,000-square-foot office and shop space will be completed at the same time. The overall dimensions of the building are 630 feet by 200 feet. The hangar will stand 46-feet tall at the eave and approximately 52 feet at the peak.

A time lapse video showing the 175,000-square-foot facility currently under construction from start to its present status is now available for viewing. The sequence of images used to compose the video was pulled from a camera mounted on a nearby hangar.

View the time-lapse progress of the maintenance hangar and shop space construction in the video below.

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.

The overhead crane will cover approximately 1,200 square feet of shop space, allowing for better work flow. Fixed stands will be installed adjacent to the cranes, giving the technicians safer access to the larger landing gear during maintenance. A new 300-square-foot dedicated paint booth and a 400-square-foot new cure room are included in the expansion increasing the work capacity and improve the time it takes for accessory units to go through the paint process.

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 hangars and expanded shop areas will be able to accommodate the volume of maintenance, modifications and completions work our customers require.

Contributed by Jerry Cable, Accessory Tech Rep

Dry felt with damage to D-ring.

What-is-left-after-dry-felt-is-removed.

Corroded-felt-groove-area.

 During recent inspections, Duncan Aviation accessory technicians have found corrosion on the pistons in the Main Actuator. This area becomes susceptible to corrosion when there is a lack of lubrication on the piston rod felt wiper. Without lubrication the felt absorbs water and begins to corrode the piston and aluminum housing. If corrosion develops, the piston must be sent out to be re-chromed at a minimum of a six-week downtime or replaced with a new unit. There is no repair for the aluminum housing, it must be replaced.

When the aircraft sits idle, the actuator is fully extended. This is when the shaft should be lubricated. Lubricating the piston rod felt wiper is a Chapter Five item. Refer to the Learjet Maintenance Manual for the proper procedures and frequency.

Scheduled to open in August of 2013, Duncan Aviation's Accessory Shop at its Lincoln, Neb., location, will gain approximately 6,300 square feet with the refurbishment and expanded footprint of its service area. Read more about how Duncan Aviation is investing today to be prepared for tomorrow in the Spring 2013 issue of the Duncan Debrief.

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.

Darrell Cermak, Rotable Inventory Manager

Duncan Aviation Parts & Rotables Sales 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 Hawker 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 Hawker 125 airframe that have been known to not make the next Time Before Overhaul (TBO).

	Sequence Valves (AIR48540-1) Sequence valves are required Overhaul items and have to be overhauled at the required Chapter 5 Interval. However, sometimes they do not make the TBO due to seal failure and contamination of the hydraulic fluid, leading to internal slide and sleeve failure.
	Starter Generators (23080-005 & -064) Starter generators are exposed to a lot of abuse while operating in a constantly vibrating environment with lots of heat. These conditions over time take their toll, leading to problems, such as not coming on line, unable to be paralleled and premature brush wear.
	Maxarets (AC65216 & AC65218) The Hawker 125 series aircraft utilizes an axle-mounted Maxaret to control skid conditions. It is a required overhaul item and needs to be removed at the necessary intervals. It is not uncommon for valve wear and seal failure to cause leaking, requiring removal before TBO. When removing Maxarets, be sure to use the proper Maxaret extraction tool and procedures to avoid unnecessary damage and expensive overhaul costs.
	Valve Refrig Bypass (104968) The aircraft uses this bypass valve to regulate cabin temperature to the desired setting. Due to ever-changing cabin temperatures, this valve is always opening and closing. Failures such as inop, slow to operate and does not modulate result in unwanted cabin temperature ranges.
	Airbrake Actuator (AIR46520-2 & 21-2) Just like the sequence valves, the Airbrake Actuator is a hydraulic unit with many seals. These seals have been known to fail before the next required overhaul interval and may cause the unit to be exchanged earlier.

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 inventory availability 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.

Duncan Aviation is still a Hawker Service Center

 In light of the recent changes in the industry for Hawker operators, I want to remind you that Duncan Aviation continues to provide comprehensive Hawker aircraft service and support at all Duncan Aviaiton locations around the world. We are an industry leader in Hawker maintenance, structural repair, landing gear/component overhauls, engine MPIs, avionics upgrades, paint and interior. Our experience and capabilities are second to none. For more information about your options as a Hawker operator, contact any one of the many Duncan Aviation Hawker experts.

Darrell Cermak is a Rotable Inventory Manager located at Duncan Aviation’s Lincoln, Nebr., facility. He specializes in the Hawker 125 and Falcon airframes. His aviation career began in 1995.

Contributed by Jerry Cable, Accessory Tech Rep.

When experiencing an intermittent nose wheel steering fault, the first thought is generally, “what is wrong with the steering servo, computer, valve, actuator or strut?” But don’t overlook a very important part of the system—Weight on Wheels (WOW). This system is very easy to test and replace. It has been my experience that WOW is the cause for more than half of these types of faults.

The WOW System

Most aircraft utilize some type of WOW Sensor or Switch that activates when the aircraft is on the ground. They come in many different sizes shapes and technologies and can be in various positions in the aircraft and landing gear. The one thing they all have in common is they complete the circuitry required to do many other things on the aircraft. From thrust reversers to nose wheel steering and many in between, the aircraft relies on these switches to operate correctly. A faulty or incorrectly adjusted switch/sensor may cause vital systems to not function or function intermittently.

The Wow System

There two basic types: mechanical switches and proximity sensors. Mechanical switches are easier to test; however, they fail more often because they rely on mechanical contacts to create the circuit. Proximity sensors do not utilize a direct mechanical contact but instead use circuitry to decipher when the magnetic field is interrupted. The proximity sensors are more reliable, but more difficult to troubleshoot. Most mechanical switches are either open or closed. Yet due to the circuitry of a proximity sensor it can be partially open and partially closed at the same time. So a proximity sensor that is known to be good but set to an incorrect clearance can cause very erratic behavior of other systems.

Systems that are run through the WOW system are exclusively used either in the air or on the ground, not both. Systems that utilize the WOW system include but not limited to, thrust reversers, nose wheel steering, trim and autopilot.

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.

Contributed by Jerry Cable, Accessory Tech Rep

Challenger landing gear requires a detailed inspection at 60 months for the 600 and 601 and 96-months for the 604 and 605. It must then undergo a 120-month restoration for the 600 and 601 and 192 month for the 604/605.

The reason for these inspections is to check for cracks, wear and corrosion. Years of water, dirt, salt air, fluid and various other electrolytes have taken their toll. The gear is very susceptible to corrosion and even though steps may have been taken to lessen the effects, some corrosion still forms.

Corrosion is normally found throughout the gear but can often be repaired using standard repair schemes available in the CMM or through engineering concessions. Sometimes, however, the corrosion has exceeded the limits of those repair tolerances.

Some of the more severe corrosion found during these inspections is detailed in the following photographs.

	MLG Trailing Link CL600/601 Axle Bore corrosion found in 35% of the restorations we perform.*
	MLG Side Strut Pin CL600/601 Corrosion on OD radius found in 50% of restorations.*
	MLG Hinge Pin CL600/601 Corrosion on the ID mating with brake line swivels found in 70% of the restorations.*
	MLG Oleo Pin CL600/601 Corrosion on the ID found in 65% of the overhauls.*
	MLG Oleo Cylinder CL600/601 ID corrosion found in 50% of the restorations.*
	NLG Main Fitting CL600/601 Corrosion under steering sleeve found in 50% of restorations.*
	NLG Plunger Tube CL600/601 Corrosion, lower band mating with axle found on 75% of restorations.*
	NLG Axle Barrel CL600/601 Corrosion mating with plunger tube found on 75% of restorations.*
	NLG Steering Cuff CL600/601 Corrosion in the ID Bore found in 60% of restorations.*
	NLG Axle Transverse Bore CL600/601 Corrosion found on 50% of the restorations.*
	NLG Steering Rack CL600/601 Tooth damage going to caster mode found during 90% of restorations.*
	MLG Side Strut Rod End CL600/601 Bearing bore corrosion found in 85% of the restorations.*
	MLG Side Strut CL600/601  Bearing bore corrosion found in 85% of the restorations.*

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.

Contributed by Jerry Cable, Accessory Tech Rep

Click images to enlarge

The Hawker 125 series business aircraft utilizes an axle-mounted Maxaret to control skid conditions. The Maxaret is installed in the axle and is driven by a small splined shaft in the hubcap. These units are required overhaul items and need to be removed at the necessary intervals. To avoid potential bill backs or high overhaul costs, it is recommended that the proper tooling and procedure for removal be followed.

The Maxarets are held in place with a retaining nut in the axle. Dirt, debris and rust can also collect in this area creating a tight seal and snug fit. It is tempting to grab a hold of the shaft of the Maxaret with a pair of pliers to yank it free, but doing so will cause damage to the shaft of the Maxaret.  The damage could result in the need to replace the shaft if the drive cap can not be installed due to damaged gear teeth. The cost to replace this part is estimated at about $2000.

To prevent unnecessary damage, loosen the nameplate bolts and use the special extraction tool engaged under the heads of the bolts. See photo 3. Using this procedure only takes a few extra minutes, but will prevent any damage to the shaft of the Maxaret, avoiding added expense. The Maxaret installation and extraction tool can be purchased from Hawker Beechcraft (part number A125529).

Duncan Aviation provides accessory unit repairs and overhauls for the most popular business aviation airframes. We work on tens of thousands of accessory units providing some of the fastest turntimes in the industry and the highest quality of repairs and overhauls.

Search our accessory capabilities.

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.

Contributed by Dave Schiver, Airframe Tech Rep.

Within the last few weeks at Duncan Aviation, we’ve had discussions about tire changes on Learjets and other make/model aircraft and what criteria to use when replacing a tire. It sounds pretty simple, but there is a lot of confusing and conflicting information you should be aware of. 

CMM & AMM Mismatch

There are aircraft maintenance providers that will replace your tire using only the Component Maintenance Manual (CMM) and have the 8130 state that as their only reference data. But when was the last time you looked in your aircraft maintenance manual (AMM) to confirm that this met all the stated requirements?

The AMMs for Learjet 31, 35, 36 & 60 series call out the replacement of ALL the self-locking nuts when re-assembling the wheel halves. Yet the 20 series and 55s do not, at least not at this time. I would be surprised if this is not changed in the next revision.

Wheel & Tire Assembly

Are you aware of what criteria were used on your last tire change?

There is one P/N wheel and tire assembly that can be used across more than one model line. During your last tire change, if only the CMM was referenced and this assembly was installed on your Lear 31, it is possible it does not meet the airworthiness standards for your aircraft since the CMM does not state to replace all the self-locking nuts on every tire change as it does in chapter 32 of the AMM for that model.

Also note, we have seen other OEMs place other requirements such as eddy current and Chapter 5 Requirements on wheel and tire assemblies over and above what the CMM calls out that are installed on their aircraft.

At the end of the day, who is responsible for ensuring ALL requirements are met when installing ANY part on an aircraft? That’s right… the one doing the installation. In most cases, that is probably YOU.

Help Us Serve You Better

When contacting Duncan Aviation's Accessories Department to send a wheel and tire assembly in for a tire change, please state which aircraft maintenance manual you would like us to reference to ensure we comply with all the requirements that you, as the installer, will need.

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.

Jerry Cable, Accessory Tech Rep

Messier is aware that the current configuration and greasing procedure of the main landing gear (MLG) main fitting may not allow grease to be forced into the joint between the MLG main fitting and trailing link assembly. The lack of grease on these parts can lead to abnormal and excessive wear on the bushings. A supplemental greasing procedure and associated tooling has been developed by Messier to lubricate this joint. The procedure will allow grease to reach the affected areas, but is somewhat cumbersome to perform.

Bushing Design Improvements

Messier and Bombardier are in the process of releasing Service Bulletins that improve the bushing design to eliminate the need for a supplemental greasing procedure. It is recommended that this improvement be installed during the next 96-month or 192-month inspection interval.

The improvement not only rectifies the problem of grease passage to the proper area but also implements a new installation procedure. The installation procedure, which uses wet sealant on all areas of the bushings, will help to alleviate the corrosion problem present on many of the main fittings under the bushings.

While the bulletins have not yet been released, the improvements can be implemented and approved through a Messier concession and subsequent Bombardier SRPSA approval. Consider these improvements and the next scheduled inspection to prevent further or future problems with the MLG that could lead to costly repairs or even more costly replacement. Contact Duncan Aviation's landing gear experts for more information. 

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.

Contributed by Jerry Cable, Accessory Tech Rep

The Learjet 35/36 model and some Learjet 20s are wired in such a manner that there is potential to cause problems with the Master Caution Box (MCB), P/N 2610855-29 and 2618055-30, which may result in incorrect troubleshooting of the MCB and Glare Shield. It could also result in complete failure of the MCB.

For example: three Transistors (Q210, Q211 and Q212) are mounted in the nose of the aircraft. Transistors Q210 and Q212 control light intensity of the Pilot and Copilot Glare Shield assembly. Transistor Q211 is for a 3.4Vdc regulated voltage Power Supply for the Master Caution Box; that supplies power to the Electronic Integrated Circuit (IC) inside the MCB. The ICs are voltage sensitive with a maximum rating of 15 Volts direct current (Vdc). If transistor Q211 fails, the voltage will be driven to 28 Vdc, nearly twice the maximum voltage that the ICs can handle. This can result in the failure ICs in the MCB.

Care should be taken when installing the new MCB to ensure that unregulated voltage (above 5Vdc) is not applied to the MCB (failed Q211); causing a complete failure of the new MCB. Prior to replacing the MCB; Q211, insulator and hardware should be checked or replaced.

If in doubt, these transistors are easy to access and cheap enough to warrant changing them at regular intervals.

Recommended procedures when replacing or troubleshooting the MCB

1. Check the GROUND leads from the master caution connectors to aircraft ground. This is to insure Master Caution Box has proper grounding. Problems caused by grounding issues can be numerous; from completely inoperative and intermittent to erroneous caution trips. Troubleshooting this problem can be a daunting task but will save time and money in the long run.
2. Verify TRANSISTOR Q211 is working properly and replace if needed. A failure of this transistor will allow the unregulated voltage to be applied to the MCB, leading to a complete failure when power is applied to the aircraft.

For exact details including “pin outs,” connectors, meter readings, etc.; contact Duncan Aviation’s Accessory Electrical Team Leader Tim Smith.

Now through the end of January 2013, save $100 on your next repair, overhaul or functional test on your electrical and pneumatic units. Download the details and coupon here. 

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.