5 Most Common Repairs for the Turbo Twin Commander

a Twin Commander flying over clouds

Twin Commanders are exceptional airplanes with rugged durability and reliable performance and speed. In the late 1970s and early 1980s, Gulfstream Aerospace (the manufacturers of Twin Commanders at the time, though it was acquired by Chrysler in 1985) released several enhanced turbine powered models that they called “Jetprops”. The term jetprop is synonymous with turboprop, but Twin Commander’s jetprops represented the most advanced Twin Commanders ever produced. 

The models in the Jetprop line included:

  • Model 840
  • Model 980
  • Model 900
  • Model 1000

Of the Jetprop line, the model 1000 was the most powerful and advanced aircraft. Shortly after the Model 1000 was produced, production was halted on Twin Commanders completely. Despite Twin Commanders no longer being produced, there are still over 1,000 Twin Commanders flying or on the market today, and they represent an incredible opportunity to own and operate an exemplary airplane.

The Twin Commander brand has made a concerted effort over the last 10 years to ensure parts availability and extensive inventories for maintaining Twin Commanders. Owners and operators should not have an issue locating the right part for repair or maintenance. Here we provide a table of contents to help you navigate through the most common repairs and preventive measures to look out for, with the Twin Commander.

Pressurization Duct Leaks

Pressurization issues are unfortunately common with Twin Commanders. The pressurization ducts go from the back of the airplane, underneath the floor, to the front of the airplane. These ducts are incredibly well insulated, making it challenging to know if a leak is occurring.

All pressurized aircraft develop small cabin leaks from time-to-time that are mostly inconsequential. However, the larger leaks prevent the pressurization system from reaching max differential to provide the crew and passengers with the lowest possible cabin altitude.

Pilots should be able to spot low cabin pressure differential and request a pressurization check. However, a qualified MRO can also assess if a larger leak exists following a maintenance or inspection event.

The typical leak sources are the bases of the rudder pedals and flight control pedestals, as well as the wing roots. Repairing leaks at the rudder pedals/flight control pedestals is a relatively easy maintenance job. Not to mention, Twin Commander has developed a custom kit with new rubber boots for the pedals and flight control pedestals that do a much better job of sealing the bases and preserving pressurization.

Rudder Cable Replacement

Your Twin Commander has rudder cables going over pulley systems, and they are subject to fraying. Even with the latest service bulletin or a custom kit—where larger pulleys are in place to address the fraying issue—fraying can still occur. If the rudder cables break, the pilot won’t have rudder control.

During your 150 hour inspection, your MRO will check for any fraying or breakage by running a cloth over the cables to see if they snag. If they do, your MRO will talk with you about replacing the cables or, if you haven’t upgraded to the latest service bulletin or a custom kit, they will discuss upgrade options with you.

Fuel Leaks

Age causes airplane fuel leaks. That’s the case with any aircraft, not just Twin Commanders. However, because all Twin Commanders are older, airplane fuel leaks are a common repair issue that we see.

Fuel inherently causes dry rotting of the fuel tanks. If the airplane isn’t flown often, or if it’s left parked without a full tank, the tanks can dry out and begin to crack. Once the fuel tanks have cracked, that’s when leaking will occur. If you notice fuel leaking , your MRO should address the issue as soon as possible.

One way to extend the life of your fuel tank is to keep the airplane moving. Secondarily, top the fuel tank off at the end of a flight or at least keep the tank at ¾ full so the tanks aren’t allowed to dry up. Fuel keeps the tank moist, which allows the tank to stay pliable and healthy.

The lifespan of a fuel tank is around 20 to 30 years, so if your tank is in need of repair but is already 15 to 20 years old, you should replace it altogether.

Nose Gear Repair

You may notice that your nose landing gear shimmies. If it does, there are a handful of reasons why. The most common cause for a pilot to report a nose wheel shimmy is an out of balance nose tire. While this may be the simplest problem to diagnose and the easiest to repair, it does occasionally require a complete tire change to remedy.

If the nose gear centering cam pin has a faulty o-ring, or if the center cam pin port in the strut is elongated, fluid will seep down into the groove of the anti-shimmy pads and lubricate the pads. Any sign of leakage should be quickly addressed by your MRO and worn parts should be replaced.

Another reason why the nose gear may be shimmying is that the steering collar halves may need to be tightened to increase the spring force on the pads. The Aircraft Maintenance Manual notes a 24-step process for checking if there is the correct number of shims to get the proper amount of friction, and this process should only be handled by a qualified Twin Commander MRO.

Twin Commander Windshield Repair

Replacing a windshield is an expensive endeavor, and it’s one that should be avoided. If a windshield fails, you’re looking at an estimated $58,000 in parts costs plus around 45 hours in labor costs to replace the windshield (prices as of April, 2021, subject to change).

Delamination of the windshield is what you should keep an eye out for during your pre-flight inspections. Delamination is when the inner and outer panes of the windshield begin to separate internally which can allow air and moisture ingress to occur. If this begins to occur, you’ll notice what looks like a milky substance building up between the two panes. You may notice that the milky substance subsides when the plane is sitting out in the sun or a dry area, but you will inevitably notice its return when the environment changes.

Pilots can still operate with a delaminated windshield, to a certain degree. As long as the delamination isn’t blocking the pilot’s vision or has lead to a crack, the aircraft can still be flown. However, it’s imperative that a qualified MRO inspect your windshield to ensure further delamination doesn’t occur. 

Pre-Flight Steps to Extend your Twin Commander Windshield Life

The best way to avoid having to pay costly repairs for a broken windshield, is through preventive measures. Below are some steps you can take to avoid an airplane windshield crack and extend the lifespan of your Twin Commander’s windshield.

Step 1: Verify Windshield Heating Prior to Takeoff

The Aircraft Flight Manual recommends that if the temperature is below 5 degrees Celsius, turn the windshield heat on and keep it on any time outside temperatures are expected to be below the 5 degree Celsius mark. It is up to the pilot’s discretion for continued operation. There are varying thoughts on windshield heat operations, and when to use or not use it. Your experience in your aircraft and your training from a qualified instructor will help prolong the windshield’s life.

Step 2: Watch your Overhead Meters

During your pre-flight inspection, watch your overhead ammeter when the windshield heat cycles. If you have a fully-functional operating system, you should see a slight change in the ammeter readings or a change in direction of the whiskey compass. If you begin to see a drastic change as the windshield heat cycles, that will indicate a deeper issue that will need to be addressed.

If the windshield heat isn’t working at all, or if it’s causing the fuse system to overheat (which will be indicated by your meters), have a qualified MRO look at it ASAP so you avoid a costly replacement bill.

Step 3: Vent Excess Heat

If your Twin Commander has been sitting in the heat with the cabin door closed, the cabin will be retaining excess heat. Unlike your automobile, your aircraft will be experiencing a sudden and sometimes quite drastic heat change as you climb to altitude. As with anything, sudden shifts in temperature (i.e. going from a hot airstrip to cold air at high altitude) can cause stress issues that can shorten the life of your windshield.

If you’re in an environment with extreme heat, take a little extra time during your pre-flight and let the cabin vent the excess heat out prior to take off.

If you notice a discrepancy in your heating system at any time, have an MRO look at it as soon as possible.

Understanding the Twin Commander Windshield Warranty

It’s important to understand the warranty that comes with your Twin Commander windshield. In 2019, Twin Commander extended its windshield warranty. The warranty states that all new windshield purchases and installations completed at a Twin Commander Factory Authorized Service Center will have a 36-month pro rata warranty—almost double the length of the previous warranty available for Twin Commander windshields.

The Twin Commander windshield warranty only applies to windshields installed by Twin Commander Factory Authorized Service Centers.

Winner Aviation is a Twin Commander Factory Authorized Service Center

At Winner Aviation, we are one of 14 Twin Commander Factory Authorized Service Centers in the country. Have your Twin Commander inspected and repaired by a team you can trust. Contact us today to discuss your next inspection with us.

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