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Aviation History
1995
1995 - 0058.PDF
AIR TRANSPORT ATR plans modification to tackle icing issue after US flight tests JULIAN MOXON/PARIS RAMON LOPEZ/WASHINGTON DC ATR IS PROPOSING a mod ification which would double the size of the wing de-icing boots on all ATR 42s and ATR 72s. The idea follows research at Edwards AFB, California, into the causes of the crash of an ATR 72 at Chicago in October 1994. ATR says that, while the tests left no doubt that the type complies with all current icing-certification reg ulations, there are concerns that an abnormal icing condition may have occurred involving unusually large water droplets. This could have contributed to the asymmetric wing icing which is believed to have led to loss of control of the aircraft. The US Federal Aviation Administration is expected shortly to lift the ban on ATR aircraft fly ing in actual or forecast icing, which was imposed after the crash. It will issue a new airworthiness BOEING BEGAN a 1,000-flight service-ready testing programme of the Pratt & Whitney PW4084-powered 777 on 29 December, 1994, almost two months later than hoped. It says that cyclic testing is going better than expected, however. Approval for extended-range twin-engine operations (ETOPS) with the 777 when the twinjet enters service with launch cus tomer United Airlines in June is dependent on successful comple tion of the 1,000-flight-test pro gramme now under way. Boeing had hoped to begin ser vice-ready testing soon after the first flight of the aircraft, the fourth 777, on 28 October. The manufacturer says that it is still on track for certification of the 777 in mid-April and delivery of the first aircraft to United in mid-May, but directive at die same time setting out new cockpit procedures for the crew to follow if certain icing phe nomena are observed. ATR says that the de-icing boots would be increased in size so that they would extend over 14% of the chord instead of 7%. This would involve removing the composite leading edge, which extends back to the wing spar, and fitting larger rubber boots. "It could be done in a matter of hours," says ATR. ATR's proposal to the FAA also calls for interim procedural changes for despatch and opera tion of the aircraft into known or forecast icing conditions and addi tional training for pilots and despatchers. In the Edwards tests, a Boeing KC-135 water-spray tanker was flown ahead of the ATR 72, releasing two sizes of water droplet measuring 40-70 microns and 180 microns in diameter. The latter is not covered by any certifi cation requirement, but is repre sentative of the droplets thought to have been present at the time of the accident. The tests revealed that a recog nisable pattern of ice builds up on the cockpit side-window when the aircraft flies into the larger droplets. This, and other signals such as abnormal aerodynamic behaviour, could be used by pilots to anticipate ice build-up. "We're facing something that has not been seen before," says an ATR source. "It is like the windshear problem that suddenly appeared in the 1970s and 1980s". There is opposition to the ATR plan, however. The Association of Flight Attendants (AFA) wants the FAA to keep the existing AD in place until a satisfactory design change is found to eliminate ATR control problems during icing con ditions. It claims that the Edwards AFB tests confirm problems with the aircraft's design (which it does not specify). The US Air Line Pilots Association agrees. Its head, Randy Babbitt, calls the ATR plan "unacceptable" saying that "...we don't believe sufficient test data has been generated to substantiate their position". He rejects the side-window detection procedure because it would require an encounter with icing conditions before the condi tions can be detected. "That's what we're trying to avoid — its like touching a burner to see if the stove is on," Babbitt says. Gilbert Defer, the ATR 72 pilot for die Edwards AFB flights, says: "Never before have so many people who were on the ground, diou- sands of miles away, claimed to know so much about what hap pened in an aircraft that I was fly ing...I can assure you that the aircraft responded well in every test environment...the plane remained under full control at all times, in all types of severe icing conditions, including freezing rain." • PW4084-powered 777 undergoes service-ready tests /ere Boeing aims at 111 ETOPS approval by June notes that it has until the aircraft enters service in mid-June to complete service-ready testing. The manufacturer says that cycles are being accumulated faster than expected, with up to 12 flights a day being completed. Plans call for a high-time PW4084 to be installed after 500 cycles have been logged and, towards the end of service-ready testing, almost 100 flights will be operated on representative city- pairs by flight and ground crews provided by United. Boeing has accumulated more than 540 flights and l,430h on five P&W-powered 777s. Delayed certification of the General Electric GE90 is now expected in mid-January and will be followed by the first flight of a GE90-powered 777, destined for British Airways. • FLIGHT INTERNATIONAL 11 - 17 January 1995
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