199309-1972-85 Twin Commander 690 Series

less than Cheyennes, King Airs, and Con- quests of similar vintage. There are reasons for these lower asking prices. Some have to do with the airplane's somewhat justified reputation as a mainte- nance hog with out-of-sight parts prices and terrible parts availability. This prob- lem is now being effectively addressed by the new owners of the twin Commander's type certificates, Twin Commander Air- craft Corporation (TCAC [19003 59th Drive, N.E., Arlington, Washington 98223; telephone 206/435-9797]). Problems with the -5 engine have also dogged the 690s. One involves the stator for the third-stage power turbine wheel. The stator's central seal had a history of rubbing against the turbine wheel, causing damage to both stator and wheel. No acci- dents or uncontained failures of the tur- bine wheel ever occurred due to the bad stator, but the potential was there. AD 93- 05-09 requires that these stators be replaced with one of a newer design that eliminates the problem. Garrett has a pro- gram, offered through its authorized ser- vice centers, which offers replacements for $4,975 per stator, or $9,950 for both engines; there's no labor charge. The Bendix pneumatic-sensor fuel con- trollers were also a service issue. These were used up to the 1979 model year and could cause power fluctuations. The prob- lem was traced to a combination of mois- ture, freezing temperatures, and polluted outside air entering the sensor and block- ing its normal movements. A 1973 SB fixed this by routing bleed air through the unit, and almost all affected airplanes have had T-22 • SEPTEMBER 1993 this work done by now. Garrett switched to Woodward mechanical fuel controllers in 1979, partly in response to complaints by operators who had bad experiences with the Bendix units. Woodward controllers were also offered as a retrofit to earlier 690s. Though the Bendix wrongs have been righted, the memory lingers. Wood- ward-equipped 690s, 690As, and 690Bs are worth about $25,000 more than those with Bendix fuel controllers, according to the Bluebook. Now that the 690 series is two decades old, a great reckoning faces many twin Commander owners: They're looking at engine overhauls. At about $141,000 per engine, this can have a devastating effect on resale value or the wallet, depending on the attachment of owner to airplane. Garrett has come to the rescue with its Century+ (Century Plus) program. Under this program, the -5's original, 3,600-hour TBO can be extended to 5,400 hours. There's a cap on the cost of the TBO exten- sion, which is $73,550 per engine. Garrett emphasizes that this is a not-to-exceed price, which means two things. The total cost may be less than the cap, and the cost is less than what an overhaul might be. It also means that the prospective buyer of a 5,400-hour- TBO twin Commander must be prepared to pay more. The TBO extension amounts to a big work package and incorporates many of the maintenance items mentioned earlier. Included are new first- and third-stage stator assemblies, a new compressor assembly, modifications to turbine wheel- bearing mounts, new torsion shafts, and new gears for Woodward propeller gover- nor gears. Another Century+ program puts a cap on the -5's 1,800-hour, scheduled hot-sec- tion inspections. That price is $45,825 and, like the TBO extension, includes parts, labor, and testing. One more Garrett program now in the works is essentially an engine swap. This would replace the -5s' hot sections with those of Garrett's 820-shp TPE331-10-501K engines. Details aren't firm on this plan as yet. If it comes about, the 690s and 840s eligible for the upgrade would pick up about 25 knots in cruise, climb 200 to 300 fpm faster, and burn just 4 percent more fuel in return. What's more, the cost of the -10's hot-section inspection would be about half that of a -5's. The swap would amount to a transfor- mation of a 690-series airplane to a Com- mander 1000, which can cruise at just under 300 knots. The 690 series has a strong, stout air- The main gear rotates 90 degrees to fit into the nacelles. The cabin includes a one-step entry, a forward potty, and "picture windows." AOPA PILOT' T-23 8 .. · frame, but there is a fly in the . _ ointment. It's a big one: The main wing spars have to be inspected for corrosion. The twin Commander spar problem first surfaced after a July 25, 1990, accident in Sweden involving a 680E model. The acci- dent was attributed, in part, to fretting cor- rosion of the main lower spar cap. A stiff- ener at the back of an engine firewall apparently rubbed against the lower spar cap, which led to cracks, which led to a fracture of the spar cap. TCAC issued an S8 requiring an inspection of the critical area and the cleanup of any corrosion. This problem affected the oldest twin Com- manders, the piston-powered models built before 1960. But it was soon learned that another type of corrosion affected other twin Com- manders-more specifically, the 500, 680, 681,685, and 690 models, up to the 690B. The corrosion in these models was also found at the lower spar cap. There are two principal reasons for the corrosion's affect- ing this critical area. One was the breakdown of the zinc chromate treatment that Rockwell applied to the spar components during assembly. The other is the lower spar's design, which uses a stainless-steel strap to strengthen the spar's ability to withstand large, posi- tive-G flight loads. Evidence shows that as the zinc chro- mate breaks down, the aluminum spar cap comes in contact with the stainless-steel strap. Over the years, dissimilar-metals corrosion can set in. Notice we said can set in. According to a March 1993 report of378 inspections by TCAC service centers, 59.5 percent of the airplanes showed no corro- sion. Only 3.4 percent of the airplanes showed corrosion levels greater than 100 percent of allowable service limits. To solve the problem, TCAC issued SB 208A, which set up a spar inspection schedule and guidelines for replacement of the spar cap and stainless-steel strap. If no corrosion was found or there was less than 50 perceJ1t of certain corrosion limits, 208A requires repetitive inspections at 12- month intervals. If there is more than 50 percent of the corrosion limits, replace- ment of the spar cap and strap is required. Of course, replacement negates the need for further inspections. TCAC came up with a replacement spar cap kit that includes a new cap and strap. The replacement procedure involves removal of the cap and strap, cleanup of the old zinc chromate layer, and applica- tion of an epoxy resin coating to the cap. The stainless-steel strap is given an elas- T-24 • SEPTEMBER 1993 tomeric coating, and the cap and strap are reinstalled. These new coatings will last much longer than a zinc chromate treat- ment, should prevent the cap and strap from ever coming in contact, and should eliminate the possibility of dissimilar-met- als corrosion. The Federal Aviation Administration liked TCAC's SB and issued AD 91-08-09, which made its provisions mandatory. A proposed AD is now in the works that would stretch the inspection intervals up to 36 months for a corrosion-free spar and 30 months for spars with less than 50 per- cent of allowable corrosion limits. Because inspections are mandatory- and expensive-many twin Commander owners are now ending their problems by installing the new spar kit, which termi- nates the AD. A TCAC program offers a new cap and strap for free. There's a $70,000 labor charge for the turbine twin Commanders and a $50,000 charge for the "short-wing" piston-twin Shrikes affected by the AD. A spar kit offered by Aviadesign of Camarillo, California, will also take care of the problem. The kit, called the "Saunders Super Spar," is available as a supplemental type certificate (STC) and employs a design quite unlike the TCAC stock replacement. According to Aviadesign's David Saunders (who designed spar straps for older King Airs), the kit uses aluminum spar caps with stronger metallurgy, fewer built-in stresses, and better temper than the stock caps. In addition, Aviadesign's kit uses an external aluminum strap attached to the spar cap but mounted on the lower wing surface. Saunders shuns the use of stainless-steel straps, calling them "the bad guys in the first place." The Aviadesign kit costs $79.500 and includes parts and labor. For further infor- mation, contact Aviadesign at 375 Durley Avenue. Camarillo, California 93010; tele- phone 805/981-3940. As if this weren't enough. another pro- posed AD would require that the spar caps of certain 690Bs be inspected for defective grain structure. TCAC has yet another SB to address this problem, and Aviadesign has an STC'd fix. In this case, the situation has to do with a batch of bad extrusions. About 80 690Bs have the questionable spar caps, which apparently were manufactured under poor quality-control conditions. The bad caps have fine-grained aluminum with what's called an equi-axed structure, which is quite unlike the large-grain, elon- gated structure a spar requires. Without the correct structure, stress corrosion (1 •Classic lines, an all- business cockpit, and more than a few quirks distinguish the turbine Commanders. AOPA PILOT· T-25 G ·., cracking can take •.. '=I" place-as it has .. ' , in a few 690Bs. If you have a bad spar cap, then replacement is necessary. About 30 TCAC spar kits have been installed. It takes about 1,300 man-hours (around two weeks) to do the job. So far, some 14 Aviade- sign kits have been completed. So the 690 series has its share of spar problems, and any prospective buyer must be aware of them. Ready for another poten- tially big problem? It's the fuel cells. To comply with the spar cap SBs or AD, you have to inspect the spars, right? To do this, you have to remove the 690 series' rubber fuel cells. There are 22 of them, and after 10 years or so, you can bet that some have cracked or otherwise become unusable. Sometimes the act of removing them will crack the cells. At any rate, new cells are about $3,000 apiece. Overhauled ones are some- what less. (The Propjet 840s have a big advantage in this depart- ment. They have wet wings, so no rubber cells.) Actually, the 690 series' fuel system is very, very simple. All 20 wing- mounted cells feed into two fuselage- mounted cells. There's a simple on/off fuel switch (plus the usual emergency shutoff valves at the engine firewalls) and a single fuel-quantity gauge. There's no crossfeed and no transfer pumps. For pilots, the fuel system is exemplary in its user-friendliness. However, for an out-of-practice mechanic, relpoving and replacing those fuel cells can be a nightmare. As we go to press, the FAA an- nounced another notice of proposed rulemaking concerning the Comman- ders' wing flap cables and master pul- leys. The intent is to establish an AD mandating an inspection of these com- ponents and replacement of any dam- aged cables, cable guides, or pulleys. Now that we've explored all the 690s' warts, it's important to remember that TCAC supports the airplane very well through its network of authorized ser- vice centers. The Aviadesign kits can be T-26 • SEPTEMBER 1993 installed at three approved facilities. Garrett has done an exemplary job in addressing the -5's problems in as eco- nomical a fashion as possible. Pilots new to the twin Commander should, of course, receive type-specific training. The simulator-based training offered by FlightSafety International in Oklahoma City is an excellent way to become familiar with the airplane's normal, abnormal, and emergency pro- cedures. One quirk, though-the hydraulic nosewheel steering-will take a little real-airplane practice to master. Push softly on a rudder pedal, and the hydraulic steering system turns the nosewheel. Push just a little harder, and there's plenty of braking action. The neophyte twin Commander driver is easily spotted by his lurching turns and sudden stops. The airplane featured in the pho- tographs accompanying this article is a 1975 690A operated by Horizon Auto- motive Group of Roseburg, Oregon. This is a firm that manages a network of West Coast Honda and Mazda dealerships and has interests in the lumber and wine business. The com- pany bought its Commander from Eagle Creek Aviation Ser- vices at Indianapolis' Eagle Creek Airpark. The purchase price was $500,000. Horizon looked at Conquest Is, C90 and E90 King Airs, and Cheyenne IIs during its air- plane search. It found the Con- quests and King Airs too high priced. The Cheyenne cabin was too small for Horizon's tastes, and there was also con- cern about the Cheyenne's longitudinal stability. Horizon bases its Comman- der-N72VF-at Santa Ana's John Wayne/Orange County Airport in California. Typical mission profiles include fre- quent trips to Roseburg, Port- land, Coos Bay, Bend, Eugene, and Astoria, Oregon. Hori- zon's pilot, Gordy IIer, Jr., says he usually carries two passen- gers and that trips to Oregon take just two hours. He usually flies between 22,000 and 28,000 feet and trues out at 270 knots. What does he like about the airplane? "It's a good single- pilot airplane," says IIer. "And its stability makes it great for instrument flying." IIer, whose previous experience includes stints as a Learjet captain, says "It's real nice to be back in a high-per- formance airplane," when asked about the 690A. What do the passengers like most about N72VF? "The speed," says lIer. "Since we can do our trips so fast that they're not standing up a lot." Horizon's Commander has just about everything a prospective buyer should look for in today's turbine twin Commander market. First off, the 690A itself is desirable because it's old enough to warrant a lower asking price, yet has some of the more important improvements. For example, the 690As were the first to . have electrically heated glass wind- shields and known icing approval. The straight 690-its predecessor-uses an alcohol spray bar and has an antiquat- ed-looking instrument panel. Secondly, the 690A has a 5.2-psi pressurization system; the 690's is 4.8. Finally, the 690As came with more soundproofing than the 690s. N72VF has had the spar replacement (performed by Eagle Creek, an autho- rized TCAC and Garrett service center), plus a new paint job and interior. It also has the SAOO-hourTBO conversion and Commander-Aero's "Aerodyne" wing- lets, which give the wing tips the look of a Propjet 840. When the interior work was done, extra soundproofing was installed. The high-pitched scream of the Garrett tur- boprops has always been a sore spot with many operators. With the pro- peller arcs so close to that flat-sided fuselage, extra soundproofing is essen- tial for achieving bearable interior noise reductions. N72VF's inside noise level was such that a passenger on the rear bench seat claimed he could hear cock- pit conversations. By the way, that rear bench seat is more or less directly beneath the air- plane's center of gravity. This means that passengers seated there are sub- jected to a minimum of rolling and yawing in turbulence-another reason why passengers think it's the best seat in the house. Our flights included a sampling of instrument weather, and we can attest to the airplane's excellence as an instrument platform. On our returns to the Eagle Creek airport, we flew the localizer approach with no trouble at all managing systems, power, or config- uration. In spite of its rocket-ship image and high performance, it should be easy for the pilot of a piston twin to transition into a 690. Prior to landing, the hydraulically actuated landing gear can be lowered when speed slows to 200 KIAS. Then power is reduced to 200 shp per side (there are no torquemeters; power information is provided on gauges reading in horsepower), followed short- ly with the first increment of flaps. Pattern speed works out to approxi- mately 120 to 140 KIAS, and final should be flown no slower than blue- line-llS KIAS.Over the fence, our air- speed was about 100 KIAS,followed by somewhat graceless, but acceptable, touchdowns. Veterans, however, show off by making greasers with the nose angle as high as a Skyhawk's. No doubt about it, the airplane has fine manners. Anyone considering a 690-series Commander would soon realize he or she is getting a whole lot of airplane for the money. You may not have the interior room of a King Air or the speed of an MU-2, but you will have one of the classiest airplanes around, with record-setting performance and considerable ramp appeal. 0 MEET THE NEW OWNERS New life for a classic design Ted Smith designed the first pro- totype of what was to become the twin Commander in 1946. His company, Aero Design and Engi- neering Corporation, certificated the design in 1952. Through the 1950s, the company cranked out several powerful, high-wing piston twins. All of them were powered by geared Lycoming engines rang- ing from 260 to 340 hp, and one of them, the 680E, was the world's first pressurized light twin. In 1958, the Hockwell-Standard Cor- poration bought Aero Design. The company name was changed to Aero Commander. Hockwell-Stan- dard merged with North American Aviation in 1966, to form North American Hockwell. In 1981, Gulfstream American bought North American Rockwell. During this whole period, the twin-and beginning in 1976, single-en'gine-Commander line grew and diversified, and sales of turbine twin Commanders alone totaled 2,122 air- planes. Because of the ownership changes, twin Commanders have been known as Aero Commanders, Rockwell Commanders, and Gulfstream Commanders. But they're all the same basic airframe. But in 1985, Gulfstream (Gulfstream Aerospace, by then) stopped making twin Commanders. For four years, twin Com- mander owners and operators languished under dwindling product support from the Gulfstream organization. Price and avail- ability of parts, always a very sore issue T-28 ' SEPTEMBER 1993 TCAC General Manager James Matheson with twin Commander owners and opera- tors, worsened during this time. Many felt that a dearth of maintenance solutions to the technical problems of their aging air- planes would make it unsafe or uneco- nomical to fly their twin Commanders. This all came to a happy end in Decem- ber 1989, when Twin Commander Aircraft Corporation (TCAC) of Arlington, Wash- ington, bought the type certificates for all twin Commanders from Gulfstream. TCAC, a branch of Precision Aerospace, now heads up a worldwide network of 41 TCAC-authorized twin Commander ser- vice centers (27 of which are in the United States) and a parts inventory worth more than $11 million. Most of the service cen- ters have experience with twin Commanders dating back to the Rockwell days. TCAC General Manager James Matheson sums up the company philosophy by saying, "We're try- ing to create a renaissance here." By that, he means attacking parts-availability problems, dras- tically lowering parts prices, and ensuring that TCAC strengthens its technical support and engi- neering capabilities. One example of this isTCAC's spar cap replacement kit, men- tioned in the accompanying article. TCAC also publishes "Captain Commander's Bargain Bulletin," which lists the latest reductions in parts pricing. In one issue, reductions in the prices of some 25 different parts were announced. Heated windshields are down from $25,980 to $23,695. Boost pumps are now $1,735, down from $3,006. Starter-generators were $6,999 apiece; now they're $6,450. Even the land- ing-gear bungees are marked down. They were $4.25 each; now they're down to $1.20. TCAC also sponsors an annual sympo- sium for its authorized service centers. "When Gulfstream let the twin Com- mander go," Matheson says, "there was still a great personal attachment of owners to their airplanes but also a strong feeling that the airplane had no real parent. That's what Twin Commander Aircraft is all about. We're in it for the long run." -TAH ( (