|Title:||Autoflight failure, Airbus A319-131, G-EUPV|
|Micro summary:||This A319 experienced uncommanded failure of its autoflight systems.|
|Event Time:||2001-08-09 at 1650 UTC|
|Publishing Agency:||Aircraft Accident Investigation Board (AAIB)|
|Publishing Country:||United Kingdom|
|Site of event:|
|Departure:||Belfast International Airport (Aldergrove), Northern Ireland|
|Destination:||London Heathrow Airport, London, England|
|Airplane Type(s):||Airbus A319-131|
|Type of flight:||Revenue|
|Executive Summary:||During the two previous sectors, this aircraft had exhibited discrepancies between the airspeed indications displayed on both pilots' Primary Flight Displays (strip type airspeed indicators). In each case, the crew compared their indications with the Standby Airspeed Indicator, and determined that it was the No 1 (commander's) indication that was incorrect. |
During the first manifestation of the problem, the commander's airspeed indicator (ASI) display was reported to be reading 20 kts in excess of the first officer's indication. After landing, engineering inspection was carried out and Air Data Reference (ADR)1 and Inertial Reference (IR)1 tests revealed no faults. A ground scan also revealed no faults with the system.
During the subsequent sector, the discrepancy reappeared, with the commander's airspeed indication being 20 kt less than that of the first officer's. This event occurred during a Heathrow to Belfast International sector and the aircraft landed at Belfast uneventfully. Belfast was not a location where the operator had any immediate repair or replacement capability. After evaluation of the symptoms, it was considered that Air Data/Inertial Reference Unit (ADIRU) number 1 was effectively inoperative as it was thought to have been the source of the erroneous airspeed indications presented to the commander.
The aircraft's Minimum Equipment List (MEL) did not allow dispatch with an inoperative ADIRU1, but did allow for ADIRU3 to be inoperative for dispatch. As the three ADIRU units are identical in function, it was decided to transpose ADIRU1 and ADIRU3 in order to allow dispatch of the aircraft for one sector back to its base at Heathrow, in accordance with the MEL (para 34-10- 01) requirements. The circuit breaker for ADIRU3 was then pulled and collared, thus rendering the unit inoperative for the flight. Ground tests of the ADR interface, IR interface and an automatic landing system 'LAND' test were carried out satisfactorily prior to departure.
The sector was uneventful until the aircraft was on the intermediate approach for Runway 27L at Heathrow. Whilst at 6,000 feet, speed 210 kt in cloud, there was uncommanded disengagement of both the Autopilot and Autothrust systems. The commander took positive manual control of the aircraft. The disengagements were coincident with multiple Warnings and Cautions on the Electronic Centralised Aircraft Monitoring (ECAM) display. Multiple crew procedures were therefore displayed for action.
The commander reported that the pattern and sequence of these failure messages, which included ADR Disagree, ADR Fault, Auto Flight Rudder Travel Limit and Flight Augmentation Computer (FAC)2 amongst others, did not indicate a single recognisable failure. It was noted that the airspeed discrepancy was again present, with the commander's indication being 15 kt different from the first officer's and the Standby ASI.
The commander issued a PAN call to advise ATC and the crew carried out the appropriate ECAM actions as displayed. The crew made reference to the Quick Reference Handbook (QRH) procedure for 'Unreliable Airspeed'. The approach was continued with the aircraft in 'Alternate Law' flight control mode. By design, this mode reverts to 'Direct Law' once the landing gear has been selected down. The commander carried out an uneventful landing in 'Direct Law' using configuration 3, with an approach speed appropriately increased in accordance with the manufacturer's recommended procedures. The weather at the time was a surface wind from 320° at 10 kt, visibility 4,000 metres in rain, with broken cloud base 1,800 feet, temperature +14°C.
After landing, the crew halted the aircraft when clear of the runway to fully assess the situation prior to taxiing to the parking stand. Once parked, the passengers deplaned normally.
|Learning Keywords:||Systems - Autopilot/Autothrottle|
|Systems - Flight Instruments|
|Systems - Navigation Systems|
|Close match:||Instrument failure, Airbus A319-131, G-EUOB|
|Electrical sparks, Boeing 757-2YO, G-OOOX|
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