Engine, interior upgrades revitalize older Learjet 25s

Aviation International News » April 2007
March 28, 2007, 6:05 AM

The ranks of small business jets are about to swell with the imminent buildup of new sub-10,000-pound jets certified to FAA Part 23 regulations. Priced from $1.5 to $4.5 million, these jets include the newly certified Cessna Mustang and Eclipse 500, and the in-development Adam A700, HondaJet and Embraer Phenom 100.

There is nothing inherently wrong with Part 23, and plenty of jets are certified to those rules. But more stringent transport-category Part 25 regulations mandate a higher level of performance, especially during takeoff after engine failure. And if Part 25 is important to a prospective jet buyer, he might want to consider an older transport-category-certified airplane upgraded to operate in today’s airspace, with modern avionics and fresh interior and paint, at a cost that sits squarely in the middle of the new Part 23 jet price range.

A small company in Denison, Texas, has figured this out and is selling Part 25-certified Learjet 24s and 25s at various upgrade levels. Why wait for a new Part 23 jet, wonders Best Jets president Roger Humiston, when you can buy a Part 25 Learjet that outperforms the new jets by a huge margin and is ready to fly today?

Humiston’s modernized Learjets are called Best Jets 21st Century Learjet 25s, and they come in three iterations: silver, gold and platinum, all of which include new paint and interior. The platinum Best Jet–the most expensive iteration–features the Universal Avionics EFI-890R flat-panel avionics upgrade with Vision 1 synthetic vision and engines upgraded with a long-life solid-spool compressor rotor that doesn’t add to performance but dramatically lowers engine operating costs.

The gold-edition Best Jet includes the solid-spool rotor upgrade but not the Universal Avionics system, while the silver edition uses the legacy engines without the new rotor. Both the silver and gold versions include RVSM, dual Garmin GNS 530 navs and GDL69 with XM satellite weather and Bendix/King KMH 980 TCAS 1/EGPWS. A $150,000 Stage III hush kit system is included in the platinum and gold editions.

Under the direction of Humiston’s wife, Kate Woolstenhulme, Best Jets’ specialists have upgraded the Learjet’s interior dramatically, with new one-piece headliner and one-piece sidewall shells that add a modern, elegant look to the cabin. Custom carpeting, Townsend Heritage leather seats and Lou Martin window shades make the Learjet 25’s six-seat cabin equal to that of any modern jet.

Woolstenhulme and team took advantage of the location of the Learjet’s potty seat, opposite the entry door, to craft an enclosed lav using pocket doors that slide out from the bulkhead aft of the seat and a door that closes off the cockpit. The bulkhead also is thick enough to allow installation of an LCD monitor in the cabin.

There are roughly 500 Learjet 24s and 25s still in good condition, Humiston said. The shorter and better performing Learjet 24 can undergo the same modifications as the 25. Best Jets can produce 18 airplanes a year at the company’s facilities, which include the interior shop, engine overhaul facility and heavy maintenance repair station.

Humiston recently sold 80 percent of the business, including his Best AeroNet contract fuel operation, to Phoenix Associates Land Syndicate for $4.5 million in cash plus three million shares of restricted common stock and options for 15 million shares. The sale helped provide funding for the 18-per-year production process.

The advantages of buying an older Learjet 24/25 versus a newer jet come down to performance and certification. Humiston is a strong proponent of Part 25 certification and its performance guarantees, a distinction that he believes buyers of Part 23 very light jets don’t understand. Unlike many jets certified under Part 23, the Learjet airframe has no life limit. And the Learjet 25, especially Best Jets’ Platinum Edition, outperforms many jets at a much lower price while still offering modern comfort and avionics.

As an example, Best Jets is selling a Platinum Edition Learjet 25 for $4 million (certification of the Universal EFI-890R package is scheduled for the second quarter). Cessna’s Citation Mustang entry-level jet costs $2.5 million, with seats for six (one pilot, five passengers). The closest new jet in price to the Best Jet Platinum Learjet 25 is Cessna’s CJ1+, at just over $4 million.

These jets are slower than the Learjet 25 and offer similar range capability. The Mustang provides high-speed cruise of 340 knots; the CJ1+’s is 384 knots, while the Learjet 25 cruises at 450 knots. Of course, the Learjet 25 fuel flow at that speed is about a third more than the CJ1+’s and almost two-thirds more than the Mustang’s, but both Cessnas’ turbofan engines are less powerful than the Learjet’s General Electric CJ610 turbojets.

In terms of comparable performance, the two jets that come closest to the Learjet 25 and that are still available new are Raytheon Aircraft’s Premier IA and Hawker 400XP. The $6 million Premier IA seats seven total, one less than the Learjet 25, has a maximum altitude of 41,000 feet, 10,000 feet less than the Learjet 25, and about the same high-speed cruise but with about 350 pph lower fuel flow. The Hawker 400XP, at more than $7 million, seats nine, can fly to 45,000 feet and also cruises at 450 knots while burning about 300 pounds less per hour than the Learjet 25.

The Hawker 400XP’s Pratt & Whitney Canada JT15D-5s are closest to the CJ610’s power output, although the Pratts are fanjets while the CJ610s are less efficient pure turbojets that need hushkitting to meet Stage III noise standards. The Premier IA is a Part 23 airplane; the Hawker 400XP is certified to Part 25.

In practical terms, is there a market for a jet that is three decades old yet still costs millions of dollars? Do fresh paint, an elegant interior and the most modern avionics package make an old Learjet 25 worth that much money? As with any product that’s for sale, the market will answer such questions. So far, Best Jets are selling, and the company has already completed 12 airplanes.

Best Jets 21st Century Learjet 25 Upgrade Options chart

GE’s Solid-Spool Rotor

A few years ago, the U.S. Air Force had a problem. It needed to replace the aging fleet of T-38 Talons, a capable trainer powered by General Electric’s bulletproof J85, the military version of the CJ610 that powers early Learjets. When the Air Force couldn’t find a suitable T-38 replacement, top brass decided that the airplane had some life left, but there was a nagging problem with the J85, and if GE could fix that problem, then it might make sense to stick with the T-38.

The problem with the J85 and the CJ610 is the design of the compressor rotor. The eight-stage compressor rotor consists of a stack of eight discs and eight spacers, and each stage is attached to the rotor with 70 bolts. The engine runs fine with this compressor; performance is not a problem. But when a compressor blade suffers damage, from FOD or a birdstrike, it has to be repaired or replaced.

The only way to get at the damaged blade is to remove the engine from the airplane, crack open the engine core, disassemble the entire compressor rotor assembly to get to the disc with the broken blade, repair or replace the blade, balance all the discs, reassemble the rotor, install the rotor in the engine, then reinstall the engine in the airplane.

GE engineers decided that with about 8,500 J85s in the field, it would be worthwhile to design a solid-spool compressor rotor to replace the original rotor. The solid-spool rotor’s blades mount into the rotor disc, which means blades can be individually replaced on-engine, without having to remove the engine from the airplane, saving hundreds of hours of labor just to fix a little FOD problem. The solid-spool rotor has 800 fewer parts than the original rotor.

The Air Force signed a contract to buy the solid-spool rotors so the T-38 could keep flying until 2040. And GE decided that if the solid-spool rotor was such a great idea for the J85, why not offer it to the commercial market, for not only the CJ610 but also the Falcon 20’s CF700, which has the same core.

GE stopped overhauling CJ610s in the 1990s, however, so it needed to find a company willing to offer the conversion. There are plenty of companies that overhaul CJ610s and CF700s, but none expressed much interest until Roger Humiston raised his hand. Humiston had already started an FAA repair station for CJ610 work at his Best Jets Learjet maintenance and refurb facility in Denison, Texas.

Replacing the original rotor with the solid-spool rotor involves more than just swapping parts. The clearances with the new rotor are far tighter; blade-tip clearance is just two thousandths of an inch, versus 12 to 14 thousandths with the original rotor. So the new rotor and its blades need to be machined to match the compressor case using a precision grinding machine built specially for this job.

Luckily, the Spanish Air Force stopped flying its fleet of J85-powered F-5s, which freed up a $50,000 Landis grinding machine and the tools that go with it. Humiston scooped up the Landis grinder and a bunch of other special GE tools, along with George Ottendorf, former GE test pilot and program manager on the CJ610, CF700 and J85, and Dale LaBrue, a long-time GE small-engine expert and the mechanic who hung the CJ610 on the first Learjet 23. “We’ve put together a major center for the CJ610, CF700 and J85,” said Humiston, president of Best Jets.

The solid-spool rotor was first certified commercially for the CJ610-6, which powers earlier Learjets, but there is likely a larger market for the solid-spool rotor in the CJ610-8A, according to Greg Brand, GE’s program manager for the CJ610 and CF700. GE is working on the certification program for the -8A engine solid-spool rotor as well as for the Falcon 20’s CF700.

In addition to the lower maintenance costs, the big advantage of the solid-spool rotor is lengthened TBO. For a -6 engine that complies with all GE Service Bulletins, the solid-spool rotor doubles the TBO to 10,000 hours from 5,000 hours.

The -8A and CF700 solid-spool rotor program will raise TBO to 12,000 hours. “This doesn’t affect the hot-section inspection,” Brand said, and these still come at 1,000-hour intervals. However, installing GE’s new thermal-barrier-coated combustion liners helps lower the cost of hot-section inspections because the liners now last for 2,000 hours.

These engines, Brand said, “are going to be around for a long time. We’re excited about offering upgrades that will help them stay around.”

SpiritLear Continues March toward Certification

Spirit Wing Aviation of Guthrie, Okla., is still working on modifying Learjet 25Ds with Williams FJ44-2C engines and has logged 260 hours in the flight-test program. Certification remains pending, and according to the company, minor changes to the program are under way.

The SpiritLear 25D involves more than swapping out the Learjet’s original General Electric CJ610 turbojets with the Williams turbofans. Structural modification of the engine support beams moves the new engines aft 16 inches and outboard four inches. A new engine mount yoke, pylons and skin doublers are designed to preserve the Learjet 25D’s damage-tolerant airframe.

The conversion should cost about $2 million, not including the price of the airframe. At long-range cruise speed of 430 knots, the SpiritLear burns 670 pounds per hour less than the original 25D and with six passengers will fly 1,700 nm, about 700 nm farther than the 25D. The increased efficiency stems from not only the  greater efficiency of the engines but also the improved airflow over the wings and drag reduction gained by their relocation.

Other improvements include full-time engine inlet de-icing and wing leading-edge heating, a triple-redundant pressurization system and reduced cabin and external noise.

Certification of the SpiritLear 25D, originally planned for early 2001, is now scheduled for this year.   

Bringing the Learjet 25 up to Speed

Upgrading the Learjet 25’s cockpit to a modern three-LCD instrument panel is no small task. Stevens Aviation’s Nashville, Tenn. facility took on the job, its second Universal EFI-890R upgrade program. Stevens Aviation’s first EFI-890R installation was in a Beech King Air 200, a Part 23 airplane. The Learjet 25 installation has its own set of challenges; in addition to Part 25 certification issues, there are 14 supplemental type certificates involved with the Learjet package.

The Learjet also has a physical constraint, a large cabin outflow valve on the forward bulkhead that juts a fair distance towards the instrument panel, limiting
the depth of instruments that can be installed. Fortunately, the EFI-890R displays fit, but just barely.

Stevens Aviation planned to begin flight-testing the Learjet 25 installation this month, with full certification expected by year-end.
The following equipment is being installed in the Best Jets 21st Century Learjet 25 Platinum Edition:
• Universal Avionics EFI-890R three-display installation
• Universal UNS-1L FMS
• Universal TAWS A or TAWS B
• Universal Vision 1 synthetic vision
• RVSM with J2/Kollsman air data system with J2 altitude select for the AFCS
• Dual Rockwell Collins AHS-1000 system
• L-3 Communications GH-3100 Electronic standby instrument system with
   magnetometer and PS835D emergency battery
• L-3 SkyWatch HP
• DB audio system with voice-activated intercom
• Universal RCU and Collins CTL-23
• Collins VHF-22A com
• Collins VIR-32 nav
• Collins DME-42

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