Guy Norris/LOS ANGELES
Boeing is developing a series of design changes for the 757-300 to reduce the potentially greater risk of tail-strikes affecting the stretched aircraft.
The -300 will be 7m longer than the current -200 production model and is almost exactly the same length as the 767-300 widebody. "Tail-strike is a concern, and we're doing several things to mitigate that," says 757-300 chief project engineer, Dan Mooney. Several early tail-strike events on the -200 series prompted at least part of the initiative to remove the risk from the outset of design work. Tail-strike incidents on the 757 were greatly reduced following changes to training procedures.
The -300 will be fitted with a version of the retractable tail-skid developed for the 767-300 and 777. A body contact sensor will augment the protection provided by the skid and will alert the crew to a more serious contact on rotation or touchdown. The tail-strike indicator, as it will be called, will consist of a small, frangible foil extending down from the fuselage. If the foil makes contact with the ground a message is flashed upon the engine-indicating and crew-alerting system (EICAS) display.
"As long as there's no indication the crew won't have to perform an air-turn back," says Mooney. Current regulations stipulate an immediate return if any indication of a tail strike is detected. Boeing believes that the new indicator system will save the often unnecessary cost of returning to land without compromising safety.
Boeing also plans to make it harder for the crew to accidently scrape the tail on landing by linking a pitch-attitude sensor to the spoiler deployment system. "If the pilot is abusing the landing and coming in nose high and too slow, the sensors will delay spoiler deployment," adds Mooney. Spoilers pro- duce a significant nose-down pitch moment on the 757 in landing configuration, and by modifying the spoiler-control schedule, Boeing hopes to achieve greater envelope protection on touchdown.
The tail-strike protection, as well as other features, were defined as part of the final configuration which was confirmed on 18 October. The milestone marks the start of a rapid acceleration for the -300 programme which sees the start of the first major subassembly in December. "We're still doing some design work and releasing drawings," says Bruce Nicoletti of 757-300 product marketing.
The first flight is due in mid-1998, with deliveries to German launch customer, Condor, starting in January 1999.
New features include the advanced cabin interior and vacuum lavatory design developed for the next-generation 737. "Flexible" seating can be "rapidly" converted from six-abreast to five-abreast.
Source: Flight International
