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Aviation History
2004
2004-09 - 0924.PDF
AIR TRANSPORT SAFETY GUY NORRIS / LOS ANGELES NTSB urges A30O600 rudder fix Investigation into 1997 American Airlines incident reveals flight control system allowed stabiliser to be overloaded The US National Transportation Safety Board (NTSB) has urged design modifications to the Airbus A300-600 rudder travel limiter sys tem in the wake of the 1997 upset of an American Airlines aircraft which overloaded the vertical sta biliser and led to its replacement. The NTSB says its renewed inter est in the data from the incident on Flight 903 "resulted from prelimi nary findings in its investigation of the 12 November 2001 accident in volving American Airlines Flight 587". In a letter to US Federal Aviation Administration adminis trator Marion Blakey, it adds that, al though the cause of the fatal acci dent in New York is still being investigated, "information to date indicates that the vertical stabiliser Thales Avionics will deliver its first digital head-up display (D-HUD) to Airbus in September, and installa tion on the first aircraft -an A340 - will start in December. The system will be offered as a standard option on all Airbus fly- by-wire aircraft - including the A380 - with the A340 the first to be certificated, set for next year. Thales was selected by Airbus over rival Rockwell Collins Flight Dynamics last year. According to the French avionics company, certi fication on the A320 family should follow no later than three to four was subjected to large aerodynamic structural loading during the acci dent sequence". It also adds that the safety issues discussed were "not a factor in the Flight 587 accident". In the 1997 incident, an in-flight upset at an altitude of 16,000ft near West Palm Beach, Florida triggered the aircraft's stall warning system. During the event, the aircraft rolled to extreme bank angles left and right, and was stalled several times during a rapid descent of more than 3,000ft. One crew member was severely injured and the aircraft damaged. However, it was not until five years later, during the Flight 587 crash investigation, that the inci dent aircraft's composite vertical sta biliser was inspected and found to have delamination damage. months after the A340, with the A380 another three to four months later. Several A380 customers, including Emirates and FedEx Express, have indicated they may opt for the D-HUD. Thales expects its D-HUD to enter service on an Airbus in late 2006 at the earliest, but the com pany has not specified a customer. From the first quarter of 2005, the mechanical and electrical pro visions needed to install the D-HUD will be built into some pro duction aircraft by Airbus to ensure customers can upgrade later. As with other large transport air craft, the A300-600's flight control system is designed to reduce the maximum possible displacement of control surfaces as airspeed in creases. The A300-600's rudder trav el limiter (RTL) allows up to a max imum of 30° up to 165kt (300km/h) and deflection with gradual reduc tions down to 3.5° at 395kt and above. However, investigations reveal that the RTL "cannot main tain this schedule in response to more rapid airspeed changes, such as those experienced during the Flight 903 upset", says the NTSB. Because of this, it adds, the rud der travelled in excess of its RTL design limit for about 20s. The rud der twice exceeded its design limit by about 8°, and twice by about 5°. Customers will be able to choose to provide both pilots with a HUD. Thales Avionics senior flight operations advisor Capt Reda Benlekehal says the HUD will pro vide operational benefits: "On a runway equipped with a localiser, the HUD's guidance will display centreline deviation during the take-off roll, like a para-visual indi cator. This will enable take-off [run way visual range] minima to be reduced from 110m [360ft] to 75m." He adds that during the landing roll, deceleration can be improved as the HUD displays braking force, Further investigations showed that if a pilot applies enough rud der pedal force when the pedal is at its travel limit, the effectiveness of the RTL can be affected. The NTSB says it is "concerned that such an increase in available rudder beyond the designed RTL restrictions could permit excessive rudder move ments and possibly result in high loads on the vertical stabiliser". It is therefore calling for FAA- mandated modifications by Airbus to enable the system to respond effectively to rapid airspeed changes "such as those that might be experienced during upsets and not be adversely affected by pedal forces". Airbus says it acknowledges the NTSB's recommendation and is awaiting the FAA's reaction. which "will help pilots, for exam ple, needing to comply with land and hold short requirements". The D-HUD provides informa tion using a digital liquid-crystal display (LCD) that is fed data by an optical fibre. Previous HUDs have an analogue cathode ray tube (CRT) display. The LCD HUD will have a reso lution of 1,280 by 1,024 pixels, which Thales says is better than CRT displays. Using an LCD means that it can use 50% less power than the traditional CRT unit, says Thales. PRODUCTION First A380 wing fence arrives at Airbus from Australian maker Hawker de Havilland has delivered the first wing fence for the A380 to Airbus. The 2.4m (7.8ft) high, arrow-shaped wingtip fence is being manufactured by the Australian Boeing subsidiary at its Bankstown, , Sydney, facility. For the first delivery, the horizontal wingtip and < vertical fence were connected in Australia as part of a quality assurance I testing process, but subsequent examples will be shipped separ- •• ately - the wingtips to Broughton in the UK for attachment to the i wing, and the wing fences to Toulouse for attachment on the final S assembly line. AVIONICS ROB COPPINGER / PARIS Thales A340 head-up display due in September www.fliqhtinternational.com FLIGHT INTERNATIONAL 8-14 JUNE 2004 13
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