Boeing is in the final stages of preparing its fourth 737 MAX test aircraft for a transatlantic flight to the Farnborough Airshow, where it will make its international debut by appearing in the flying display July 11-14.
The presence of the 737-8 at the show is intended to start a key marketing phase for the reengined narrowbody family. The company is on track to obtain type certification of the first of the reengined twin variants in the first quarter of 2017. Boeing, which has firm orders for more than 3,200 MAX aircraft, is running ahead of a conservative certification plan that originally targeted initial deliveries for late 2017. Boeing has advanced certification plans to the third quarter and could even edge deliveries into the first half of the year should launch operator Southwest Airlines, or possibly another early customer, be able to accept them.
Amid this accelerated time frame, Boeing is expected to bolster its portfolio by launching the 737-7X, a redesigned variant of the 737-7. Studies also are underway for a stretched 737-9 dubbed the 737-10X, which is designed to take on the Airbus A321neo. Details of the -7X development, which includes lengthening of the fuselage by 76 in., could be unveiled at the show pending the outcome of negotiations with 737-7 launch customers Southwest and WestJet. They  are expected to convert their orders to the revamped configuration.

Boeing’s fourth 737-8 test aircraft will take part in the flying display at this year’s Farnborough Airshow. Credit: Guy Norris/AW&ST

Meanwhile, flight testing of the 737-8 continues on—or slightly ahead of—schedule, with four active aircraft in the certification program. The first of these, 1A001, made its maiden flight on Jan. 29 from Renton, Washington, and its stability and control work is near completion, says MAX chief project engineer Mike Teal. The aircraft, which returned to Seattle on June 28 from California, where it underwent runway performance work at Edwards AFB, will “be done with flight tests around the end of the third quarter,” he adds.
The second aircraft, 1A002, has largely been dedicated to propulsion tests associated with the MAX’s CFM Leap 1B engine but was also used to complete the flight-loads survey. “We only did the outboard wing for the flight-loads survey because of the winglet change,” explains Teal. “Results were as expected. In fact, there’s been no drama, and testing has been going very well.” The aircraft’s next exercise will be to undergo community noise testing at Glasgow, Montana.
The third aircraft is dedicated to systems testing and propulsion work and, at the end of June, was being used for evaluation of the Leap 1B integrated drive generator. Dubbed 1A003, the aircraft also has been used to evaluate the autoland and head-up display systems.
The fourth aircraft is configured with a virtually complete passenger interior in the style of its eventual operator, Southwest. However, some instruments remain in the aft of the cabin for environmental tests, such as smoke-penetration and detection. “It is now in prep to go to Farnborough, and it has the experimental ticket on it,” notes Teal. “We are also doing customer work on it, and one of the tests . . . we call the ‘fly-turn-fly’ test in which, each day, we did eight simulated flights. The intent is to de-bug the airplane. Most of the testing is for certification, but this is aimed at [making the aircraft] customer-ready.” 
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Once 1A004 returns from Farnborough and completes its additional customer testing, it will face functionality and reliability testing in “the October-November time frame,” says Teal. At year-end, 1A004 will likely be flown to Russia for cold-weather testing. “That’s kind of the last testing we will do. It’s either Canada or Russia, but right now the plan is Russia.”
Further evaluations will be conducted late in the program on the delivery-standard Leap 1B engine with an improved low-pressure (LP) compressor configuration. The current fleet is powered by compliance versions of the -1B engine, and Boeing expects to receive the upgraded powerplants, “in the August time frame,” says Teal. “We plan on putting them on Aircraft Two, Three and Four. We won’t put them on Aircraft One because that airplane essentially [will be] done with its [test] life.” Testing will include natural icing and other minor evaluations, he adds.
Improvements were made to the LP compressor after testing indicated it was necessary for bleed valves to remain open for longer than expected to maintain adequate stall margin. “They didn’t have to be open all the time. The bleed schedules open and close the valves, so to improve stall margin, we want the bleeds closed for better fuel mileage,” Teal explains. “CFM could have certified the existing engines, and they did, but we wanted the best engines. The bleeds are open a little more than desired on the engines that are flying now, but when the final Block 2s come in, we will get the final bleed schedules that will determine the final configuration.” 
The 737-9, meanwhile, reached the 90% design release point around mid-June. “We have already started production of the stringers, which we are being sent to Wichita to Spirit [AeroSystems] for the first fuselage, and we start the first wing build in late September with first front spar load. That airplane flies at the end of the first quarter of 2017,” adds Teal.