The Duncan Download Blog: Business Aviation Advice & Observations

Submitted by Jerry Cable, accessories tech rep

Here. Fix This. 

This reminder may sound obvious, but it is amazing how many accessory units are sent into Duncan Aviation with no explanation or only very little instruction. Within the last year we’ve had a starter generator show up with no paperwork. Is it here for the 2,000 hour overhaul or 1,050 bearing change? What about the actuator with a note that simply said “repair.” Repair what? What is the squawk? When does it occur? 

When this happens we run a function test and hope the results identify the issue. However, this isn’t always a guarantee. Not all squawks can be duplicated on the bench. And many times the problem is related to other aspects of the flight or external conditions and may only fail on the bench when these conditions can be recreated. Taking note of the conditions when the component or system fails, is essential to the effective and timely resolution of the problem.

When removing any units from your aircraft, whether it’s an accessory, avionics, instrument, etc., that is to be sent in for repair or overhaul, always identify the squawk or inspection that needs attention. Having the right information about the circumstances surrounding a squawk can save your tech rep many hours of troubleshooting time and yourself a considerable amount of money.

Duncan Aviation provides accessory unit repairs and overhauls for most popular business aviation airframes. All accessory test equipment is calibrated using NIST certificate traceability. This includes three stab actuator test stands and several sets of test equipment unique to Duncan Aviation.

If you’ve ever had to hunt for a specific aircraft part, component or avionics unit, you are well aware of how difficult it is to do a thorough research, locate a reputable supplier, negotiate pricing and schedule delivery. Most of the time, you are under a strict time constraints and need the aircraft part or avionics unit now and you don’t want to deal with all the issues that can complicate the process along the way; issues, such as no available inventory, managing billbacks, no traceability documents and lack of warranty support.

Kassim Khan, co-owner of Aviation Parts & Supply, an aviation parts broker supporting several corporate flight departments, has relied solely upon Duncan Aviation for 18 years to provide the parts needed to serve their customers. “The bottom line is that Duncan Aviation has never let us down,” says Khan.

Read Aircraft Parts on Speed Dial on page 29 of the Fall 2013 issue of Duncan Debrief and find out why Kassim has only one number in his phone when it comes to finding aircraft parts. 

Duncan Aviation maintains a large inventory of aircraft parts for sale. Our streamlined services and competitive turntimes satisfy hundreds of requests throughout the world 24 hours a day, 7 seven days a week. Our many awards testify to the quality of our service.

Today we are taking a break from the typical Duncan Download blog post to do something a little different. Rather than tell you all the facts about how the Duncan Aviation Accessories area has expanded its landing gear services or explain why all landing gear service facilities are not created equal, we are going to let the numbers speak for themselves.

Here's a detailed pictograph of the Duncan Aviation's landing gear services over the last 35 years.

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 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, -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 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 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 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.

Contributed by Jerry Cable, Accessories Tech Rep

When the landing gear actuators on the King Air 90 and 200 model aircraft arrive at Duncan Aviation for their six year or 8,000 cycle overhaul, the first thing performed is the actuator screw and nut end play inspection on each actuator assembly (two main/one nose). The end-play inspection measures the play between the threads of the screw assembly and nut assembly. A large majority of the time the nut assembly will require replacement due to extended wear.

The actuator screw and nut end play inspection should be performed every 1000 cycles or 30 months, whichever comes first. The allowable tolerance between the actuator screw and nut assembly is .016 of an inch, but the actuator can remain in service up to .018 of an inch but must be re-inspected every 200 cycles. If the inspection finds the tolerance beyond .018 of an inch, the landing gear actuators must be sent in for overhaul. Keep in mind that even if the Actuator passes the end play check at 1000 cycles or 30 months, it may not pass the more stringent end play check required by the overhaul manual. The maximum allowable end play at time of overhaul is only .009" before it must be replaced.

This nut assembly wear is caused because the nut assembly is made of a bronze material that rubs against the steel screw assembly. Symptoms of extended tolerance could be a loud noise when the LG is extended and retracted. If any foreign material were to get in between the threads, this assembly will bind up and the LG will no longer be able to extend or retract.

If you should have any questions about this, don’t hesitate to contact me. To schedule your King Air 90/200 landing gear overhaul, contact your Duncan Aviation accessories customer account rep.

Contributed by Jerry Cable, Accessories Tech Rep

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.

Contributed by Bob Tooker, Quality Control / Consignment Sales Rep

Safran Power UK & Safran Power USA has developed a more reliable replacement starter generator that replaces P/N 400SG138Q. This new starter generator, P/N 23091-009, is specifically designed for the Learjet 60 aircraft and is fitted with proprietary brushes that are non-impregnated and have a slanted core type design. This design is a much-improved over the straight core brushes that have been used for many years.

Some of the technical advances of the Safran Power UK & Safran Power USA slanted core brush, P/N 23080-1983, are:

The Base Carbon

The base carbon - the mechanical properties of the base carbon in the slanted core brushes have been enhanced slightly through minor changes in the processing without affecting its commutating properties. This provides an improvement in brush life at full rated load over a broader speed range.  However, because the basic materials of the brush have not changed, the basic characteristics of the brush such as RFI and voltage drop have also not changed.

Slanted Core Design

The Patented slanted core design of the brush helps reduce the commutator wear and prevents 'grooving,' which in turn maximizes commutator life.

Non-Impregnated

A non-impregnated brush has a lower brush drop resulting in a lower brush temperature and a lower minimum speed for regulation for the starter generator.

Safran Power UK & Safran Power USA has an excellent track record regarding reliability and maintenance resulting in reduced maintenance, aircraft downtime and operating costs. Duncan Aviation is the exclusive distributor and repair station of the Safran Power UK & Safran Power USA Starter Generator worldwide. For more information, download this Safran Power UK & Safran Power USA Starter Generator information sheet or call please call 800.228.1836, international +1 402-475-4125.

Bob Tooker is an aircraft parts consignment expert specializing in quality control and export documentation. His aviation career began in 1967.

Contributed by Jerry Cable, Accessory Tech Rep.

Most definitely. Yes.

Landing gear overhauls, inspections and restorations are sometimes called a commodity service. Any shop that has received an OEM Maintenance Manual and follows FAA standards is free to advertise that it can inspect and overhaul aircraft landing gear. The FAA states "a thorough inspection of the landing gear involves the entire structure of the gear, including attachments, struts, wheels, brakes, actuating mechanisms for retractable gears, gear hydraulic system and valves, gear doors, and all associated parts. The manufacturer’s inspection procedures should be followed where applicable."

But not all landing gear service is equal. There are many additional service and capability requirements related to landing gear maintenance that can cut expenses and downtime that can’t be found at every aircraft landing gear shop.

The landing gear is a behind-the-scenes inspection, most often scheduled alongside, but taking a backseat to, a major airframe inspection. However, it can have a huge impact on the entire project’s schedule if the landing gear restoration runs into major squawks. You will want to use a shop that has invested heavily in the landing gear customer and understands full well the impact a landing gear overhaul or inspection has on an airframe inspection. After all, an aircraft can’t go anywhere without its legs.

Controlling Costs

At Duncan Aviation, we take several extra steps that help reduce costs. For example, on select inspections and restorations, we ask customers to leave the harness and brake pipes on the gear when removing it from the aircraft. By leaving the gear intact, this will save customers approximately 35 labor hours when removing and installing the gear. Duncan Aviation has also established some special pricing programs that help provide assurance to customers through pricing controls. These are just a sampling of the above-and-beyond landing gear available at Duncan Aviation.

Feel free to reach out and contact Duncan Aviation's landing gear experts. We will address the most common questions and concerns that customers ask us daily regarding landing gear work.

1. How much will it cost?
2. How long with the inspection take?
3. What about corrosion removal?

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.