Where Are You Going To Take Your MU-2 Turboprop?

Where Are You Going To Take Your MU-2 Turboprop?

MUBy LeRoy Cook

Intercontinental Jet Services Provides Factory Support For The MU-2

By any reasonable prediction, one would expect that the Mitsubishi MU-2 turboprop twin, introduced in the late 1960s and out of production since 1983, would be an “orphan airplane”, with factory parts and support no longer available. As it turns out, that’s the farthest thing from the truth. Not only is the MU-2 fleet alive and well, it still enjoys support from its manufacturer, Mitsubishi Heavy Industries, and 12 authorized Service Centers.

Among the dozen Centers worldwide, only one is owned by MHI itself: Intercontinental Jet Service located in Tulsa, Oklahoma. ICJS also hosts the MU-2’s global parts supply warehouse and can offer just about every possible service option for the venerable MU-2. Only full painting and zero-time overhauls for the Honeywell TPE-331 powerplants are farmed out; everything else, from propeller overhauls to avionics updates, can be done at the Tulsa facility.

MU2The MU-2, of course, has had a long and storied history, not the least of which are tales of “killer airplane” and uninsurability. As the only twin turboprop in its class that was designed from the very beginning to be a turboprop (all of its competitors were developed from piston-engine predecessors), it was extremely advanced for its time. The MU-2 introduced features like spoiler roll-axis control so it could be given full-span flaps, a high wing loading for both speed and a solid ride through turbulence, and over-built military-style construction with no life limit on the airframe. Mitsubishi Heavy Industries had considerable experience with building aircraft under license from U.S. firms, hence the MU-2 drew heavily on its in-house expertise.

It was the first true over-300-mph small business airplane, outpacing competitors and attracting buyers seeking the highest-performing aircraft they could afford. But, because it required somewhat different operational techniques, some of the new owners got behind the MU-2 and its accident toll became inflated by armchair experts. MHI rose to the occasion and 20 years ago it developed a PROP (Pilots Review of Proficiency) biennial pilot-proficiency training course. Thanks to that and other initiatives, the MU-2 has now earned the honor of having the lowest accident rate in its category over the last half-dozen years. It just took some respect for the aircraft and proper training in how to avoid carrying bad habits into its operation.

MU3Yes, there is a 2006 Special Federal Air Regulation 108 for the MU-2, requiring specific initial and recurrent training to fly the airplane, but it’s mostly common sense requirements, such as a functioning autopilot for single-pilot IFR, and PIC standards that would be required by insurance companies in any event. An FAA review of the aircraft’s ability to meet its Part 23 certification standards had turned up no issues. Thus, the agency imposed stiffer pilot training, and that has apparently worked.

A Place To Go

Recently, we stopped at the Intercontinental Jet Service Corporation complex on the northwest side of Tulsa International Airport, where the normal contingent of MU-2s was on the ramp. More importantly, a half-dozen were in the shops, getting upgrades and phase service. ICJS president Dennis Braner and Director of Operations Mark James gave me the tour of the sprawling facility, established in 1987. Although the company does work on other airplanes, like the Piaggio Avanti we saw in the hangar and a Beech Starship that was coming in during the next week, it is noted for being the go-to place for MU-2 service.

MU1According to Mark James, about 270 MU-2s are currently in the fleet, about evenly split between the short-body and long-body models. The longer MU-2G, with two extra seats, maingear pods and aft-fuselage strakes, first appeared in 1970 and was subsequently identified with J, L & N letters before winding up as the Marquise in 1979. The original short-body airplanes, with a sleeker fuselage that folds the maingear behind the cabin, are suffixed by B, D, F, K, M and P, finishing as the Solitaire. But, officially, these are all MU-2B airplanes, with dash-numbers to show various iterations.

The Honeywell TPE-331 engines on the MU-2 are most commonly –5 or –6 versions, with equivalent shaft horsepower ratings from 724 to 776; tailpipe thrust adds extra push. TBO is a lengthy 5,400 hours, with hot sections scheduled at 1,800-hour intervals. However, it makes sense to convert to the –10 engine at overhaul time, gaining vastly improved efficiency at altitude. The single-shaft AirResearch/Garrett/Honeywell turboprop is noted for its ease of operation and good fuel specifics, with very quick response to throttle changes.

The Ultimate MU-2

James showed us the Limited Edition MU-2 developed by ICJS, which incorporates a total makeover from the bare airframe up. Everything gets looked at and refurbished, with a new interior and paint, but the showpiece is the SAFRAN-Sagem flight deck, using digital displays of primary flight, navigation and engine instrumentation. Given the low acquisition price of older MU-2s, a fine Limited Edition upgrade can result in a like-new performer, with the latest bells and whistles, for less than any equivalent airplane. As an example, ICJS found a long-body Marquise with less than 2,000 hours total time that it is currently going through; it’ll be a prime candidate for the Limited Edition mods.

He also showed us the method of compliance for MHI’s frame-inspection service bulletin, a check for fuselage frame cracking that is to be performed every 2,400 hours, usually in conjunction with a phase inspection. Since some of the airframes have accumulated 20,000 hours in service, continuing airworthiness concerns led MHI to issue the bulletin, which may or may not become an AD. In truth, very little cracking has been found, and nearly all was on long-body models, James said. The MU-2 is a very over-built airplane. A test-article fuselage in the shop had been used for pressurization cycle testing, again showing no damage after an extended time-in-service regimen.

Mark James’ advice for prospective MU-2 buyers is to get their aircraft into an approved service center, where the aircraft is well understood, have it given a good prepurchase check, and have the pilot attend the PROP training, along with sending a mechanic to the SimCom service training course. The aircraft is a good buy, but it needs proper care and operation. ICJS sees very little corrosion, even from coastal locations, James says.

Originally, the MU-2 was test flown with Turbomeca Astazou turboprops, changed to Garrett TPE-331-25AA engines of 605 eshp for production. It was upgraded to the 705-eshp TPE-331-1-151A after two years. The aircraft was originally marketed by Mooney Aircraft in the U.S.A., but the arrangement was abandoned in 1970. The MU-2 was actually built and certified in the U.S., at a San Angelo, Texas plant, from MHI-supplied subassemblies. There, the 60-percent American components were added to the airplane, which received an airworthiness certificate from the FAA instead of the JCAB.

Understanding The Difference

The MU-2’s unusual appearance was cutting edge in 1967; fuel was carried in large tip tanks, requiring simultaneous or staged refueling to avoid tipping imbalance. Pronounced wing droop can be seen with full tanks, although the underslung tip tanks make the droop appear greater than it actually is. The double-slotted full-span flaps needed to enhance takeoff and landing performance required spoilers to be used for roll control; roll trim is provided by adjustable tabs on the flap trailing edges. James pointed out that the MU-2 is an all-electric airplane; only the brake system uses hydraulics, everything else is actuated electrically.

The fully-enclosed main landing gear stows in the lower fuselage, in large fairings on the long-body models, or behind the baggage compartment in short-body versions; large 8.50 x 10 tires are fitted. If the gear looks like it came off a Lockheed F-104 fighter, it’s probably because MHI license-built Starfighters for the Japan Self Defense Force. The 5.00 x 5 dual-wheel nosegear swings aft for retraction; after parking, it is disconnected from the steering links for towing.

The empennage is conventional, but the horizontal stabilizer has noticeable undercamber as part of its airfoil design. Dual trim tabs are provided for symmetry. The powerful rudder is adequate for handling single-engine flight, but the Honeywell engine incorporates negative torque sensing that drives the propellers toward feather automatically if power is lost. Transitioning pilots are cautioned not to crank in “aileron” with the control wheel in such a case; that would add drag by activating the spoiler. Instead, the roll trim surface is toggled while holding rudder against the dead engine.

Performancewise, the MU-2 is a rocket. The short-body airplanes can top out above 300 knots, initially climbing at nearly 3,000 fpm. Best altitudes are 20,000 to 28,000 feet, where the parsimonious TPE-331’s will use 65 to 80 gph total. Although the later-model airplanes are certificated to fly as high as 31,000 feet, RVSM certification is normally not pursued for the limited benefit it provides.

Inflight workload is light; there are no boost pumps, cowl flaps or tank switching to be handled. Fuel is fed from a center tank, refilled from the bleed-air pressurized tip tanks and outboard wing tanks, which are auto-fed on some models. Fuel capacity began as 280 usable gallons, increasing to 366 gallons in later airplanes, and to 403 gallons in the last models, which had wet wing tanks. The job of the MU-2 is to carry 1,000 pounds of payload with full fuel at 300 to 350 mph; accordingly, its handling is transport-like, not aerobatic. Trimmed up, it stays where it’s put and rides through bumps like a steamroller with its 65-lb/sq .ft wing loading. With the spoiler system, there is no adverse yaw.

As with all high-performance airplanes, the MU-2 must be flown by the numbers, in proper configuration for the phase of flight. Flap extension lowers stall speed by as much as 25 knots; a 20-degree takeoff setting is normally used. The 40-degree flap setting is reserved for maximum-performance short-field landings. The nosegear comes down as soon as the maingear touches at 85 knots or so; the MU-2 is immediately done flying.

Normal takeoff procedure is to rotate to about 7.5 degrees nose-up at 99-103 knots, looking for a single-engine climb speed of 125 knots, with 20-degrees flaps. Gear-up requires about a 15-second cycle; flaps come up above 140 knots and a typical cruise climb is at 180 knots. Descent management is easy, thanks to the drag provided by the big three-blade props turning at 2,000 rpm (1,591 with four blades). Setting up for an approach works well at about 175 knots, the retractable landing lights speed limit, with gear extension permitted below 160 or 170 knots, depending on the model. With 20-degree flaps deployed, an ILS can be flown at 120 knots.

With the proper training, the MU-2’s can safely deliver more bang for the buck than just about any other aircraft between big piston twins and light jets. And with factory support from service centers like Intercontinental Jet Service Corporation, there are no surprises in its well-known maintenance. The ICJS Limited Edition upgrade will keep it competitive for many years to come.•T&T

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    Mike October 6, 2019 at 10:54 am

    Thank you for writing this artical, greatly appreciated. The MU2 was an aircraft flown by my parents – specifically back to Australia for local buyers in the 80s.

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    Evangelo loukadakis September 7, 2020 at 3:46 pm

    Thank for this letter i love the article and the aircraft i happened to fly checks at night in a Aerostar and after my flight i will jump on the right seat at my friend’s legg and we used to loopet and roll it. Very pleasant to fly.

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