August 2012

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Early 787s face turn time constraints from brake temperature issue

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787rampturnaround.jpgAs Boeing announces it has cleared all 787 equipment for first flight, the airframer plans changes to landing gear components on later production 787-8 aircraft to improve gate turnaround operations by improving the thermal performance of part of the braking system.

Early 787s will be constrained in some quick turnaround operations if the gate arrival follows a high-energy landing that raises the brake temperature past a certain threshold. Boeing emphasized that the issue lies not with the brakes themselves, but the remote data concentrator (RDC) units on the four 787 main landing gear axles.

787maingeartruck.jpgRemote data concentrators (RDCs) are used to flow digital and analog data from remote sensors into the 787's Common Core System and replace traditional, dedicated signal wiring, saving weight and allowing increased operator flexibility.

The landing gear based RDCs were intended to accommodate the extreme heat but "did not meet expectations," said Boeing.

Adding that, "Until the new units are installed, airplane dispatch based on a lower brake temperature will be implemented."

Boeing says cooling fans can be used at the gate following a high-energy braking landing to reduce the park time necessitated by brake heat generated during landing.

Boeing has estimated that a 787-8 with 275 passengers can be turned around and prepared for departure in as little 45 minutes, though the definition of a "quick turnaround" varies depending on the needs of the airline and its operations.

Airlines often leave landing gear down for an extended time after takeoff to allow for additional brake cooling before stowage, though Boeing "has no plans to require the airlines to leave the gear down after takeoff." Adding that "dispatch procedures," which require additional cooling time at the gate, "will facilitate normal gear retraction."

Brake cooling time would vary based on airport conditions and a specific duration of time would not be specified, though brake temperature would have to return to acceptable levels prior to pushback.

787autobrake.jpgA high-energy landing would, for example, be undertaken if a higher autobrake setting were selected to reduce stopping distance on a shorter runway.

To improve turnaround time following high-energy landings that would significantly raise brake temperature, Boeing along with partner GE Aviation, who supplies the RDCs, is developing a more robust installation that will relocate the unit and improve thermal performance.

The design change will maintain the functionality of the landing gear RDCs, however Boeing will have to revise the brake control monitoring system (BCMS) software to maintain compatibility with the new component package.

The BCMS software, which is developed by Crane Co. and was previously cited as a key pacing item for the 787 program has been delivered to Boeing and installed on Dreamliner One.

Boeing expects production incorporation to tentatively occur in late 2010, which when matched up against the airframer's proposed production ramp up, could be part of the blockpoint changes expected for Airplane 20.

Though, Boeing adds that the fix will be implemented as soon as it is available and the company is still working out the exact timing of the change.

Image courtesy of Boeing

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