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Aviation History
1994
1994 - 0058.PDF
AIR TRANSPORT FAA questions 757 vortex separation BY GRAHAM WARWICK IN ATLANTA The USA is re-examining its landing-separation criteria after Boeing 757 wake-vortex turbulence was implicated in two fatal accidents involving business jets. The result could be revised weight-based separa tion categories similar to those already adopted by the UK. Boeing, the National Trans portation Safety Board (NTSB) and the Federal Aviation Ad ministration are reviewing 757 wake-vortex data, and the FAA has re-emphasised a February 1992 ruling which temporarily increased the separation dis tance required between a 757 and the following aircraft. The NTSB is still investigat ing the fatal 15 December, 1993, crash of an Israel Aircraft Industries Westwind on the approach to California's Or ange County airport. The air craft was trailing a 757 by about 3.5km (2nm). Wake turbulence from a 757 is also suspected in the fatal Decem ber 1992 crash of a Cessna Citation at Billings, Montana. The FAA divides aircraft into three separation categories, based on weight — heavy, large and small. The large category covers the widest range of air craft weights — from 5,700kg to 136,000kg. Following re search in late 1991, the FAA temporarily re-classified the 757 — the biggest aircraft in the large category — as heavy. Re-classifying the aircraft as 757 lands FAA with vortex-separation problem heavy increased the separation required between a 757 and a large-category aircraft from 5.5km to 9km and between a 757 and a small-category air craft from 5.5km to 11km, says Boeing. The FAA has also barred controllers from making the pilot of the aircraft follow ing a 757 responsible for maintaining a safe distance — as is usually the case in visual flight-rules approaches. George Green, the head of wake-vortex research at NASA, says that a business jet follow ing a 757 represents the worst case — the lightest aircraft in a category following the heavi est. He points out that the UK has revised its categories, rais ing the small-aircraft boundary to around 13,500kg and divid ing the large category into jet and commuter classes. NASA and the FAA have embarked on a programme to develop techniques to predict how wake vortices form and decay according to aircraft type and atmospheric conditions. These would allow air traffic- control systems to establish au tomatically separation dis tances for each pair of ap proaching aircraft, based on their types rather than catego ries. The aim is to increase airport capacity. The research involves windtunnel testing of aircraft pairs and flight-testing to verify software which allows any combination of two aircraft to be "flown" in a flight simulator to assess wake-vortex effects. • Collins extends Mode S applications Rockwell-Collins has ground-tested a Mode S datalink system with auto matic-dependent-surveillance (ADS) capability. Flight tests are scheduled to begin in Feb ruary with a US Federal Avia tion Administration Beech King Air 300 based at the FAA Technical Center in Atlantic City, New Jersey. The Collins system com prises an airborne datalink- processor, a differential global- positioning system (GPS) re ceiver and a modified Mode S transponder. The company says that off-the-shelf equipment has been modified to allow the ADS capability to be retrofitted into Mode S-equipped airliners. In the ground demonstra tion, GPS differential-correc tion data were transmitted to the Mode S transponder. The NEWS IN BRIEF DC-9X APPROVED Air Canada is to go ahead with a plan to modernise its fleet of McDonnell Douglas DC-9s. The airline's board of directors has approved the programme concept, clearing the way for an initial project involving structural improve ments to the aircraft. The programme will involve struc tural and system upgrades. A decision on whether to re- engine or hushkit the aircraft jas yet to be made. STILL LOOKING Finnair president Antti Potila has denied a recent report that the airline has decided to buy new aircraft, rather than re-engine its fleet of 17 McDonnell Douglas DC-9s. "We have not reached a deci sion yet," he says. JOINT VENTURE Rolls-Royce and Howmet have formed a joint venture specialising in refurbishing turbine and compressor blades and vanes for the North American market. R-H Component Technologies will be located alongside How- met's plant in Claremore, near Tulsa, Oklahoma. error data were communicated via the datalink processor to the GPS receiver, and used to correct the computed aircraft location. Corrected aircraft po sition was then communicated back to the Mode S transpon der via the datalink processor. The ADS position report was then transmitted by the Mode S transponder. Collins says future plans call for the integrated GPS/Mode S capability to be used for airport surface-surveillance. Taxiway maps would be displayed to the crew and colour-coded taxi- guidance information data- linked to the aircraft to avoid runway incursions. This will be demonstrated in April/May, the company says. The concept also forms part of a proposed GPS-based traf fic-alert and collision-avoid ance system, dubbed the TCAS 4, in which the Mode S and TCAS airborne equipment is integrated to allow communi cation of identity, intention and other information between aircraft. GPS position reports would replace the range and bearing information now used in the TCAS. Collins says that the FAA flight trials will involve both a conventional scanning Mode S secondary-surveillance radar and a distributed system co- sisting of several omnidirec tional Mode S transmitter/ receivers. The distributed sys tem is proposed for use in air port terminal-area surveillance. • Air Inter orders A319 Air Inter has ordered nine Airbus A319s and placed options for nine more. The aircraft on firm order are for delivery between July 1996 and mid-1997 (Flight In ternational, 5-11 January) and the options can be converted to orders for A320s or A321s, if required. The airline operates 33 A320s and has ordered seven A321s on order, the first due in mid-1994. It has received one A330, with four more to come over the next few weeks, and a possible ten more to follow from 1997 onwards. • 8 FLIGHT INTERNATIONAL 12 - 18 January, 1994
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