Twin Commander logo aerial shot of Twin Commander airplane


690A/B/C dorsal fin (top) and 690D and 695 dorsal fin (bottom)

One of the many interesting variations among the various Twin Commander models produced is the dorsal fin. Some models have a short fin, some long, some in-between. The fins look good and accentuate the lines of the airplane, but there can be a problem with moisture retention.

Over the years, some Twin Commander models with the longer dorsal fin have developed excessive corrosion of the skin under the fin. It's been determined that the affected aircraft had the fin installed using a fay and/or fillet seal around the periphery of the fin. In some cases the sealant application caused moisture to be trapped inside the dorsal fin, which led to corrosion of the aluminum skin. A factory maintenance alert has been issued to ensure that aircraft at risk are checked.

Twin Commander Aircraft also has engineered three Custom Kits (CK 193, 195, and 196) that greatly reduce the potential for corrosion under the dorsal fin.

The maintenance alert classifies corrosion damage in the affected area as either light, moderate, or severe. The formal definitions are:

LIGHT—Characterized by discoloration or pitting to a depth of approximately 0.002-inch maximum.

MODERATE—Appears similar to light corrosion except there may be some blisters or evidence of scaling and flaking. Pitting depths may be as deep as 0.010-inch.

SERVERE—General appearance may be similar to moderate corrosion with severe blistering exfoliation and scaling or flaking. Pitting depths will be deeper than 0.010-inch.

The alert specifies that, at the next scheduled maintenance event, remove the dorsal fin and inspect the fuselage skin underneath for corrosion. If only light corrosion is found, follow these steps to correct the condition:

  • Remove corrosion by light hand-sanding. Do not exceed the depth of defect.
  • Corrosion Convert (Alodine) reworked area.
  • Prime complete area under the dorsal with epoxy-based primer per manufacturer's instructions.
  • Reinstall the dorsal fin and fillet seal outside edge to aircraft skin using cabin pressure-type sealant as required to conceal any gaps.
  • If moderate or severe skin corrosion is found, replace the skin and then follow steps 3 and 4 above.

Be sure to notify Twin Commander Aircraft LLC, and please provide the total time on the aircraft. The information provided will assist in establishing an inspection interval for dorsal fin corrosion.

CK 193 for models 690A/B contains shims and other parts that are installed under the existing dorsal to provide channels for moisture to drain out of the cavity. It will be available at the end of August. CK 195 and 196 provide for a replacement dorsal fin. The new fin is constructed from composite laminate material that is much stronger than the plastic dorsal it replaces. The new dorsal fin also incorporates channels to disperse moisture. CK 195 is for Twin Commander models 500S, 681, 685 and 690; CK 196 is for the 690A/B. Contact your Twin Commander-authorized Service Center for more details.

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Eagle Creek delivered the sixth G950 Twin Commander at EAA's AirVenture 2015 in Oshkosh, Wisconsin. (L-R) Garmin's Dan Lind, Creighton Scarpone, and Jim Laster; Eagle Creek's Matt Hagans; 690B owner Abe Abuchowski; and Garmin's Phil Straub and Jim Alpiser.

Eagle Creek Aviation Services has delivered the first Model 690B Twin Commander with a Garmin G950-equipped cockpit. Dr. Abraham "Abe" Abuchowski took delivery of the aircraft at EAA's AirVenture 2015. This is the second Twin Commander that Abuchowski has owned.

Eagle Creek has now completed and delivered six Garmin G950 Twin Commanders including three Model 1000s, two Model 900s, and Abuchowski's 690B. The new amendment to Eagle Creek's original STC for the G950 conversion for the 900 and1000 adds all 690As and Bs (S/N 11249 and 11269-11349), 840s, and 980s, making approximately 400 more Twin Commander models eligible for the G950 modification.

"These are some awesome, awesome avionics in an awesome airplane," commented a beaming Abuchowski at the delivery ceremony at Eagle Creek's show-center display at AirVenture. "The Garmin suite makes flying so much safer and easier because it is an integrated system—the new Garmin radar, collision avoidance—everything. It improves my situational awareness, and the screens are so sharp and vivid. I'm like a kid in a candy store!"

"Completing the last phase of the STC process is something we at Eagle Creek are very proud of," commented Eagle Creek CEO Matt Hagans, "and completing the first 690-series airplane for Abe, who is a loyal, repeat customer, is personally rewarding."

"Congratulations to Eagle Creek Aviation Services for raising the bar in terms of providing customers with the very best, most contemporary Twin Commander," said Twin Commander Aircraft President Matt Isley. "And congratulations to Abe on his second Twin Commander."

"Eagle Creek knows Twin Commanders and the Garmin flight deck inside and out," noted Phil Straub, Vice President and Managing Director for Garmin's aviation products, who attended the AirVenture delivery ceremony. "And now they are putting the two together in a way that really pleases customers."

The Twin Commander Garmin G950 is a complete Garmin 1000 system with the exception of the flight control system. Among other features the Twin Commander 950 suite includes:

  • Genesys/S-Tec 2100 Digital Flight Control System
  • Synthetic Vision Enablement
  • Garmin GWX-70 Weather Radar
  • Garmin GTS-825 TAS Traffic System
  • Jeppesen ChartView Enablement
  • TAWS B
  • Garmin GDL 69SXM satellite receiver for Sirius XM weather and data
  • Garmin GTX 33ES - ADS-B Out-compliant Mode S transponder
  • Garmin GDL 88 for ADS-B In
  • Mid Continent MD302 backup attitude indicator
  • New LED electroluminescent panels

Abuchowski's 690B is the first Garmin conversion to be equipped with the new GDL 88 for ADS-B In

For more information see:

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H-D Advanced Manufacturing Company (H-D), which specializes in high-precision severe-duty components, has acquired Twin Commander Aircraft LLC parent company Firstmark Corporation. The acquisition was effective June 30.

Operations and staffing at Twin Commander will not change as a result of the change in ownership, according to Twin Commander President Matt Isley. "We will continue to provide the same high level of engineering and parts support through our Service Center network," Isley said.

The acquisition by H-D brings "significant resources benefitting Twin Commander and its customers through investments in people, facilities, equipment and strength of leadership," he added. "This partnership will continue to strengthen Twin Commander's commitment to the integrity and longevity of the global Twin Commander fleet."

Pittsburgh-based H-D manufactures highly engineered mission-critical products for the energy consumables and motion control markets. The company was founded in 2012 as a partnership among The Riverside Company, Hicks Equity Partners and Weinberg Capital Group. Firstmark is the eighth company H-D has acquired since its founding, and provides it with a new aerospace technology sector.

"Firstmark is led by an excellent management team, and we look forward to working with and supporting Matt Isley and David Devine (executive vice president responsible for Firstmark's Creedmoor, North Carolina, operations) in establishing a leading Aerospace Technology business, with Firstmark at its core," noted H-D CEO Chris DiSantis.

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