Another 737 assembly line is taking shape at Boeing's Renton, Washington plant. Line 3 will be similar to the other two already churning out almost 30 aircraft a month, except that the 737s inching down this moving line will be military - P-8A Poseidon multi-mission maritime aircraft for the US Navy.

Building a military derivative "in line" with the commercial 737 makes the P-8 different to any previous Boeing programme. "No one has done this before," says P-8 programme manager Bob Feldman. "No one has cut into a commercial line to produce a military aircraft."

The ability to produce the P-8 on the commercial 737 line was key factor in Boeing Integrated Defense Systems winning the $3.89 billion contract in 2004 to develop the replacement for the US Navy's Lockheed P-3 anti-submarine warfare aircraft. "When theP-8 is in full production we will build it in eight days, on a moving line, like every other 737," says Feldman. "The navy will get extraordinary affordability."

Boeing's original proposal was to buy a 737-800 off the commercial line, fly it a modification centre, take it apart and put it back together - as it does with the airborne early warning and control 737 and KC-767 tanker. "We have always built a green aircraft and modified it because it is difficult to do in line," says Perry Moore, director of P-8 manufacturing operations for Boeing Commercial Airplanes. "But the navy wanted us to find a way to do this.

Making a military derivative

"The navy said why buy a good aircraft and cut it apart? If you do not do something different, you will probably not win the contract," says Eric Lindblad, director, P-8 aircraft systems. "We had to take a high-powered production machine and learn how to make a military derivative."

An 11th-hour change to Boeing's MMA proposal, creating a system to allow in-line production of the P-8 has resulted in the closest co-operation yet between the company's commercial and defence businesses - a co-operation that extends to suppliers including 737 fuselage producer Spirit AeroSystems in Wichita, Kansas.

Turning the 737-800 into the P-8 has required changes to basic aircraft's structure and systems. "The typical 737 takes off, climbs, cruises for an hour and a half, descends and lands. The P-8 has eight unique flight profiles," says Lindblad. "A fair amount of the structure has been adjusted." Material gauges have been increased to strengthen the fuselage, wing and tail, and system capacities boosted to provide more cooling and power, but the biggest change to the basic 737 is the introduction of a weapons bay in the lower aft fuselage and weapon stations under the wing.

Despite these changes, at Spirit and Renton respectively the fuselage and wing for the P-8 will go through the same assembly jigs as those for the commercial 737, and at the same pace. "It has to go in and out of the jig with the commercial line move," says Lindblad.

Moore says: "Spirit has a very lean process, and will produce P-8 and 737 fuselages on the same line despite the significant differences." To avoid disrupting the flow, a downstagesubassembly position has been created at Spirit where the weapons bay and auxiliary fuel tank will be integrated before it is installed on the line. Because of the differences within the P-8 wing, separate positions will be created to finish the work.

Final assembly of the P-8 could have been performed on the existing 737 moving lines at Renton, but Boeing decided it less risky to create a separate line. It would also be easier to meet the Pentagon's security restrictions by building a separate "ITAR compliant" line that would nonetheless be available to build commercial 737s if Boeing needed more capacity.

"The real significant difference is in final assembly, and it was not worth the risk of disrupting the commercial line," says Moore. "We have a new final assembly line, but it's another commercial line, a replica of the others with the same lean production system. It's a moving line, but with extended flow times." Almost four times the number of wiring bundles in a typical 737 have to be installed, along with extra ducting and the cargo-bay auxiliary fuel tanks. "The line will not move as fast," he says. "The 737 has eight flow days, which equals eight positions. The P-8 will have eight longer flow days and three positions."

A separate final-assembly line also eases the headache for BCA of complying with the access controls demanded by the US Department of Defense's International Traffic in Arms Regulations. "We encourage commercial customers to come look at their aircraft. It would have been a logistical nightmare. The P-8 final assembly line will be fenced off for ITAR compliance," says Moore. "But it is not a dedicated ITAR line," Lindblad adds. "It will be possible to fire a commercial aircraft down that line."

There will be no similar separation at Spirit, where military P-8s will be mixed in with commercial 737s. Instead the ITAR access controls will follow each P-8 fuselage down the line, and the same will happen on the wing line. Spirit sends 737 fuselages from Wichita to Renton on railcars and method will also be used for the P-8, but the fuselage will be protected in an unspecified way.

Under the 737 production system workers stay in one position and the aircraft moves. For the P-8, small specialist teams will follow the fuselage and wing down the line to handle the differences. On the final assembly line one crew will be fully trained to build the aircraft from one end to the other, at least initially. "At rate we may go back to a more traditional arrangement," says Moore.

Construction of the P-8 final assembly line is under way at Renton. Here the two Boeings come together. On one side of the building will be the BCA assembly line, on the other the IDS static and fatigue test rigs. And all the planning will be put to the test when the first flight-test P-8, aircraft T-1, starts moving through the system later this year.

Spirit will load the first assembly jig in December, the fuselage will be in Renton by March and the aircraft will be fully assembled by August. "It's amazing how fast they build commercial aircraft," says Feldman. BCA will take T-1 through pre-flight to taxi, shut it down and deliver it to IDS, when it will be rolled into the fatigue test fixture for loads calibration and ground vibration testing.

First flight

First flight is set for March 2009, when the painted aircraft will make the short hop to Boeing Field for mission system installation. For T-1 this will mainly involve test instrumentation, about half of which will already have been installed by during final assembly, and the aircraft is expected to fly again in September 2009, making three flights from Seattle before ferrying across the country in October to the US Navy's Patuxent River flight-test centre in Maryland.

T-1, the airworthiness aircraft, will be followed by mission system (T-2) and weapons test (T-3) aircraft, as well as static and fatigue test articles (S-1 and S-2). A 700-flight, 2,300h development test programme is planned. T-2 is scheduled to fly in January 2010 and will build up to testing of the fully integrated mission system. From T-2 onwards, BCA will do a check flight and paint the aircraft at Renton then deliver it to IDS at Boeing Field.

While T-1 will be used for weapons carriage and release trials, weapons testing "for score" will use T-3 with its full mission system. T-3 will also be the performance test aircraft and a back-up to T-2 for mission system testing. T-2 will perform climatic chamber testing at Eglin AFB in Florida and T-3 will be used for electromagnetic testing at Pax River.

Although the P-8 is based on a proven airframe, full-scale static tests and fatigue testing to two 15,000h lifetimes will be conducted because of the different loads experienced. "The P-8 will spend a lot more time at lower altitude and higher g," says Pual Martin, manager P-8 test and evaluation. The S1 static airframe will be refurbished and sent to China Lake, California for full-up live-fire testing "to demonstrate it meets the vulnerable area requirement".

Feldman says: "It is not built for survivability as a commercial aircraft, so we have done significant live-fire testing and are incorporating the results into the design." A lot of the work involves the fuel system: protecting or relocating components double-wall tank liners sense and drain systems and dry-bay fire protection. "These areas have been dealt with and there are no outstanding vulnerability concerns," he says. Using a building-block approach, Boeing has conducted life-fire tests on critical areas of the airframe using surrogate structures. This has resulted in selection of an inerting system to protect the dry-bay areas around the cargo-bay fuel tanks.

The critical design review in June determined the P-8 was "green across the board" in meeting its key performance parameters, including weight and range, says Feldman. A US Navy design readiness review set for August is expected to approve the acquisition of up to four more development aircraft, T-4 to T-7, for initial operational test and evaluation beginning in April 2012.

Budget pressures

Initial operational capability of the Poseidon is scheduled for April 2013. Budget pressures have reduced the planned production rate from 16 to 13 a year, but Feldman says the line will have capacity to produce 16 or more a year, creating the possibility of accelerating P-8 deliveries to replace P-3s earlier.

Some challenges to producing a military aircraft on a commercial line remain to be overcome. For the development P-8s, the navy had to secure a waiver from US legislation requiring the Pentagon to use only domestic sources of specialty metals such as titanium - a restriction not imposed on the 737. "The commercial line is domestic specialty metals agnostic," says Feldman. "We still need a permanent waiver for production."

Unlike a green aircraft that is then modified, the P-8 will not be FAA-certificated when it comes off the assembly line.

To secure USN flight clearance, Boeing will supply a "safe to fly" plan based on its certification processes. "BCA self-certificates its commercial aircraft, so our FAA certification data will be integrated into the document required for navy certification," says Moore. An analysis to identify any gaps between FAA and navy certification requirements is to be completed this month.

"We will end up with a 737-800A - a P-8A without the mission system - which will get an FAA experimental ticket," says Lindblad. Getting the navy to sign off on this is critical to Boeing's plans to complete the "unstuffed"P-8 within BCA then deliver it to IDS for mission system installation. "We gain a lot of efficiency by provisioning the aircraft at BCA, while IDS does the plug-and-play installation," says Moore.

This production arrangement would also make it easier to allow international customers to perform mission systems installation in-country. India has been offered eight P-8s off the US production line, but Australia has decided to join the MMA programme with a requirement for 12 to 20 aircraft to replace its AP-3Cs, and will probably install the mission systems in-country. The basic P-8 airframe could also find other applications.


Source: Flight International