Trouble-free introductions of a new aircraft type are rare. The industry’s borrowing of the term “teething pains” from child development suggests some level of early operating distress is viewed as inevitable. And indeed, despite more than a century of accumulated experience by a mature and sophisticated industry, all new aircraft types still go through it.
Several years ago, when Airbus and Boeing decided to placate voracious demand for single-aisle aircraft by re-engining rather than replacing their existing types, some hope prevailed that finally the spell could be broken, or at least mitigated. After all, the A320neo and 737 Max families relied upon well-known and trusted airframes and systems, leaving the engines as the primary area for concern about teething issues.
As the first of the two families to enter service earlier this year, the A320neo played the unlucky role of industrial guinea pig in this grand experiment. By all accounts, the type could have done better. Although Pratt & Whitney’s geared turbofan technology appears to be saving fuel as promised — or, by Lufthansa’s claim, slightly better than promised — the maturity of the starting sequence and the reliability of software-derived maintenance alerts to the cockpit have fallen below expectations. Moreover, the hydraulic system and the number of “squawks” summoning maintainers to the electronic centralised aircraft monitor (ECAM) have also disappointed some users.
In Renton, Washington, the A320neo’s early struggles have not passed unnoticed. Boeing’s exclusive 737 assembly centre, however, lies less than 60km away from Everett, Washington, the home of the 787, so executives know better than to publicly gloat about their rival’s misfortunes.
“To use an overused sports metaphor, I’m not going to dance in the other guy’s end-zone and I’m not going to spike the ball on the 20,” says Keith Leverkuhn, Boeing’s vice-president and general manager of the 737 programme. Even readers unfamiliar with the ways of American football can probably get the point: Don’t be unsportsmanlike, and, worse, do not celebrate prematurely. The 737 Max is now lined up to be the next commercial aircraft to run the practical gauntlet of joining the worldwide operational fleet.
Moreover, the 737 Max also involves far more design changes than Airbus has had to manage on the A320neo. In addition to new CFM International-supplied Leap-1B engines, Boeing also adds a new winglet shape, a redesigned tail cone, electronically-actuated spoilers and 787-sized displays in the cockpit.
For airlines, however, one of the most critical, if least heralded, changes with the 737 Max is a new feature called, somewhat boringly, the onboard network server (ONS). This addition mitigates one of the glaring deficiencies with Boeing’s single-aisle product line. In the early 1980s, Boeing introduced the engine indication and cockpit alert system on the 767. Airbus developed its similar ECAM system for the original A320 several years later. Every new Boeing and Airbus widebody introduced since has also carried the technology. Even the Bombardier CSeries will enter service this summer with an aircraft health monitoring system fed by an onboard health management unit.
The Boeing 737 Max involves far more design changes that Airbus incorporated on the rival A320neo, so accurate fault reporting is crucial
But when Boeing introduced the next-generation 737 family in 1998, it didn’t add this technology; aircraft systems are still monitored and maintained in much the same way as when the type was first introduced in 1967. The avionics systems on the 737NG family remain federated, meaning they are not integrated to share and manage data. If one of the systems appears faulty, it usually requires a look inside the electrical equipment (E/E) bay while the aircraft is still parked at the airport gate. There, maintenance staff must find the culprit among an array of electronic boxes.
“For instance, let’s pick a box – the PSEU, the pneumatics systems electronic unit,” explains Leverkuhn. “On the [737]NG the overhead light goes off to say you’ve got a problem. Then the maintenance crew goes down in the E/E bay and takes a look at the PSEU box, and they say I’ve got that fault code, and they look it up.”
In most other modern airliners, such fault reports are routed electronically to a central computer. If a fault is reported by, say, the PSEU, an alert appears on a cockpit display, usually including problem diagnosis and solution.
“Instead of having to run down to the E/E bay to interrogate [a faulty system], now there’s a no-go message, for instance,” Leverkuhn says. “Imagine it’s a no-dispatch condition. Now, I’ve got it. It’s much more in line with the airplanes we have while still keeping the federated systems on the 37 that we’re familiar with.”
Boeing’s urge to upgrade the 737 Max with similar technology was balanced by the imperative to maintain as much commonality with the 737NG series as possible, thereby making the transition to the re-engined type easier for existing customers. So there would be no centralised cockpit system, which would incorporate an EICAS-style alert system. As a halfway step, Boeing connected the federated systems into the ONS.
“It’s not a true central maintenance computer,” Leverkuhn says. “It is playing a large role in getting information off the aircraft and into the airline’s hands and putting it on the displays.”
But if managed poorly, the ONS could become a source for those proverbial teething troubles. Suddenly, 737 Max pilots will have access to more systems health data in the cockpit than they have ever had before. To prevent unnecessary delays, it will be necessary to carefully sort out useful information from the nuisance messages. Some aircraft types are infamous for having a “fault-happy display”, Leverkuhn says, forcing crews to figure out what is important and what can be ignored.
“It drives the mechanics nuts because there’s a bunch of nuisance messages there that they’ve learned to ignore. We just can’t do that [on the 737 Max],” he says. “We have to have all the maintenance messages truly only show up if there’s a problem.”
To avoid the 737 Max entering service with a similar “fault-happy display”, Boeing has changed how it operates the aircraft in the flight-test programme. The pilots are closely monitoring every maintenance message sent by the ONS to the new cockpit displays, Leverkuhn says. Messages deemed unnecessary or incorrect are noted and corrected in the system, he adds.
“There is an unprecedented level in my mind in how we are attacking every squawk. If we’re in flight-test and a squawk is noted by our maintenance crews, usually maintenance fixes it and on we go. What we’re doing is making sure those are captured and brought into our system at the programme level and saying if that maintenance issue was discovered by our crews, then certainly that could potentially become an issue for our customers. So let’s make sure we are opening our aperture on everything we’re seeing in flight-test.”
In addition, Boeing has already published the maintenance manuals for the 737 Max flight-test team, Leverkuhn says. Such documents are normally published near the end of the flight-test programme, shortly before the type enters service. Boeing’s maintainers are now finding out whether the manuals are incomplete or incorrect before the airlines use them for operational aircraft.
Most of the fuel improvement promised by the 737 Max is delivered by the Leap-1B engines, which replace the CFM56 as the type’s exclusive powerplant. Though lacking P&W’s reduction gear, the Leap introduces the use of ceramic matrix composites in the hot section of an engine, along with a new generation of composite fan blades and compressor and turbine aerofoil design. The A320neo’s entry-into-service in January with P&W engines has been compromised by an uncommonly long motor-to-start sequence. To avoid causing bowed rotor damage, the engines need several minutes to cool on a quick-turn operation at an airport, although a fix is expected to be complete by October.
Leverkuhn – formerly a Boeing propulsion engineer – says the company anticipates no motor-to-start delays with the Leap-1B engines: “We’ve actually accommodated that in the [start-up sequence]. We’ve been able to accommodate [the cooling requirement] within the electronic engine controls and to stay inside those times that our customers are saying are acceptable. We’re seeing that in flight-test, too. We’re seeing we’re meeting those times.”
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Source: FlightGlobal.com
