Mitsubishi Aircraft (MITAC) has modified the first MRJ90 regional airliner since its initial three flights last November and has resumed flight tests, the company announced Wednesday. The company performed taxiing tests with the updated aircraft—Japan’s first domestically developed passenger airliner since the NAMC YS-11 regional turboprop more than 50 years ago— early this month following functional tests performed in January.

Meanwhile, MITAC has postponed the MRJ90’s entry into service for a further year—to the second quarter of 2018—even as launch customer All Nippon Airways (ANA) has conducted its first acceptance inspection of the initial delivery aircraft. The setback marks the program’s fourth major delay.

After flying the first flight-test aircraft (FTA-1) three times in November before withdrawing the machine from operation to incorporate planned structural and systems changes, MITAC confirmed the design’s “basic characteristics and functionality.” Analysis of the flights, including operation of landing gear and flaps (but not reverse thrust), verified performance according to specifications and complemented feedback from ground and taxiing tests.

In late January, Mitsubishi revealed details of planned airframe strengthening modifications after it analyzed static test results last year that indicated a weakness in the airframe and wing attachment. “Some components that join the wing and the fuselage, as well as those of the fuselage frame, would have insufficient strength” during ultimate load tests, according to the manufacturer.

As a result, it has introduced additional “plates” to reinforce original parts, a move Mitsubishi had deemed unnecessary ahead of first flight but for which the Japanese Civil Aviation Board issued a special permit in October. “But we decided to implement the upgrades during this round of feedback upgrades,” said MITAC.

Type certification requires the airframe to withstand a load 50 percent greater than the limit load, or the highest load expected during operation. Other changes consist of software upgrades to avionics, and engine- and flight-control systems. Mitsubishi plans also to apply the modifications to the second MRJ (FTA-2).

Functional testing of third aircraft—FTA-3—began in January, as MITAC installed final systems parts and cabin interiors on FTA-4 and FTA-5, both of which had entered final assembly. Schedules call for all four remaining flight-test MRJ90s to fly this year, as trials continue on two further airframes constructed for static and fatigue strength tests. Mitsubishi has completed assembly of major structures for the latter test specimen, which by late January stood on its own landing gear while mechanics installed measuring instruments.

In revising the MRJ initial delivery schedule, MITAC and parent Mitsubishi Heavy Industries (MHI) have extended the time available for flight trials in both Japan and the U.S., and testing now might continue into early 2018. The two years previously allotted by the two companies for flight testing, certification, and entry into service has now grown to at least 30 months.

Allotted time for related ground testing also increased by about 50 percent. Looking ahead, Mitsubishi said its plans called for “increasing the precision” of its scheduling and starting U.S. flight testing “as soon as feasible to propel development.”

Initial MRJ flights came after ground and engineering tests and final aircraft inspection in September and followed MITAC analysis of results from 13 formal taxiing trials conducted over five weeks from October 3. Taxiing had begun slowly in June, at the same time as ground vibration tests with second MRJ90, FTA-2, according to MITAC senior executive vice president and executive chief engineer Nobuo Kishi. Test feedback modification and technical data checks followed in July and August.

The October taxiing trials saw MITAC test emergency stop and rejected takeoff braking, nosewheel steering, and expansion of the speed range up to 120 knots. The MRJ’s three flights, at Tokyo's Nagoya Airport between November 11 and 27, covered takeoff and landing performance, ascent to 15,000 feet and descent, cruise up to 200 knots and turns, as well as landing-gear and 0- to 30-degree flap operations.

Confirming the latest delivery-schedule revision in late December, MHI and MITAC acknowledged that the review reflected additions to and revisions of original test items, as well as Mitsubishi’s joint engineering work with U.S. partners aimed at ensuring a better-integrated aircraft. The resulting new MRJ development structure intends to ensure “prompt execution” of all activities and a clear division of roles and responsibilities assigned among three engineering bases in the two countries.

Tokyo-based MITAC will look after type certification documentation and coordination with airworthiness authorities, flight tests, manufacturing preparation (including design and production) and customer support. In the U.S., the Seattle Engineering Center, an engineering arm of subsidiary MITAC America opened last August, has assumed responsibility of design development and innovating technological “solutions.”

This fourth MRJ delay, which followed discussions with U.S. partner Aerospace Testing Engineering & Certification (AeroTEC), will permit much more time for testing, both on the ground and in the air; AeroTEC's Moses Lake Test Center at Grant County International Airport in Washington state serves as the site for U.S. flight tests and support, including data analysis and report writing. AeroTEC provides data analysis, FAA certification and flight-testing services to manufacturers like Honeywell and Lockheed Martin and aircraft modification companies such as Aviation Partners Boeing and Raisbeck Engineering.

Discussions with AeroTEC stimulated caution last year as the manufacturer approached the MRJ’s flight readiness, resulting in more time devoted to checking each step. A thorough review identified a number of different items that Mitsubishi added to pre-flight test work.

MITAC officials acknowledge the value of a more pragmatic approach, even though further delay has almost certainly compromised the project’s credibility. For example, Kishi has described plans to deliver the first MRJ before July 2017 as “naïve and based on incomplete knowledge.”

MHI executive vice president and MITAC president Hiromichi Morimoto acknowledged as much upon the revelation of the latest delay at the end of last year. “We're still feeling our way along, and often lack the ability to take decisive action,” he said. “We have frequently not been able to make quick decisions when the time has come to do so.”

Kishi has also acknowledged the need for further work on the aircraft and in reaching agreement with suppliers. He said the MRJ’s landing gear and wheels require a redesign  “for better safety,” while he talks with engine manufacturer Pratt & Whitney about a revised schedule for supply of the aircraft’s PW1200G geared-turbofan powerplants.

In December, MITAC and Boeing unveiled their joint development of the My MRJ Fleet.com (MMF) customer-support service web portal. Construction also has started at MHI’s Kobe Shipyard & Machinery Works for a new factory to build MRJ wings. Workers will manufacturer main wing skins/spars and the center wing under an integrated system in the new 5,600-square-meter factory and an adjacent 25,400 square meter plant.

ANA’s mid-January acceptance inspection and approval covered the first-delivery MRJ’s “wing framework assembly” at MHI’s Nagoya Aerospace Systems plant at Tobishima. Plans call for such on-site customer inspections to happen at several points within MITAC's manufacturing process, and include the structural state of fuselage, tail assembly, wing, and other components, as well as component integration and system parts installation. Final ground and in-flight inspections will precede delivery, according to MITAC.