Zapotec ha scritto: Ad un esperto chiederi, per chiarimi ogni dubbio, se gli ADM (convertono le pressioni misurate in valori numerici che vengono trasmessi tramite bus alle ADIRU) sono parte integrante dei sensori o sono parti a se stanti. Cioè quando parlano in senso generico di "sensori di velocità" intendono, nel caso specifico, il pitot o il pitot+ADM relativo. Grazie
ciao ciao
Sensore di velocita' e' un termine improprio usato dai giornalisti.I dati di pressione dinamica prelevati dai pitot vengono inviati alle ADIRU ovvero alle unita' di controllo delle ADIRS (air data inertial ref System) che a loro volta forniscono i dati agli strumenti relativi oltreche' all'autopilota ed agli altri sistemi che li utilizzano .Un avaria alle ADIRU puo' portare alla perdita di assetto.Alcuni incidenti sono avvenuti sia per causa diretta che indiretta, dovuta principalmente alla complessa ridondanza e alla antiistintiva procedura di recupero dati (i dati delle 3 adirs possono venire inviati singolarmente attraverso switch ai PFD di entrambi i piloti e all'autopilota ).Problemi di questo tipo furono evidenziati in un incidente occorso alla Quantas dove un avaria all' ADIRU # 1 ebbe come conseguenza una repentina perdita di assetto in alta quota causata dall'autopilota.
Una AD di cui riporto un estratto fu emessa per rimarcare l'importanza della disalimentazione di un IR inattendibile:
NAV - IR 1+2 (2+3) (1+3) FAULT Note: Flight controls are in alternate law. Refer to F/CTL ALTN LAW (chapter 4 of the AFM) Turn off the affected IRs. Turn off the corresponding ADRs. Set the affected IR mode rotary selectors to OFF. Use AIR DATA switching as appropriate. Use ATT HDG switching as appropriate. Do not use speed brakes If CG above 32%: Manually perform a forward fuel transfer from the trim tank. Note: If trim tank pump is not available, do not perform manual forward fuel transfer while speed is at or below 270 kt or while in climb. Note: This operational procedure is covered by the following Temporary Revisions (TR) of the AFM: A330 AFM TR 4.02.00/46 Issue 3 (OEB N74/4) A340 AFM TR 4.02.00/54 Issue 3 (OEB N88/4 and OEB N89/4) 2. Incorporation of the appropriate AFM TR or inserting the above operational procedure or a copy of this AD into the AFM is acceptable to comply with the requirements of 1 of this AD.
Un altro incidente interessante e per fortuna senza conseguenze avvenne su un 777 di cui riporto il preliminary:
On August 1, 2005, a Boeing 777-200, which had departed from Perth, received an EICAS (Engine Indication and Crew Alerting System) warning of low airspeed, as the plane was climbing through FL (flight level) 380. Simultaneously, the aircraft�s slip/skid indication moved full right, on the PFD (Primary Flight Display). The PFD speed tape also displayed contradictory information: that the plane was approaching both the high speed limit and the low speed (stall) limit. The aircraft, still connected to the autopilot, pitched up and climbed to approximately FL410 as the airspeed decreased from 270 kts to 158 kts. The stall warning devices also activated.
The PIC (pilot in command) "disconnected the autopilot and lowered the nose of the aircraft. The autothrottle commanded an increase in thrust which the PIC countered by manually moving the thrust levers to the idle position. The aircraft pitched up again and climbed 2,000 ft." The PIC advised ATC "that they could not maintain altitude and requested a descent and radar assistance. The crew was able to verify with ATC the aircraft speed and altitude."
The PFD indications became accurate again as they were descending through FL200. The PIC attempted to use both the left and right autopilots, but had to turn them off after each one produced undesired command responses. "There were no control difficulties experienced when the aircraft was flown manually, but the autothrottle `arm� switches remained in the `armed� position."
ATC radar vectors put the plane in position to conduct an ILS to R 03 at Perth. When they reached 3,000 ft, the PFD again began indicating erroneous low airspeed information. The autothrottle again responded by advancing the thrust levers. Since the pilot can override that command, simply by manually adjusting those thrust levers, the plane was able to land safely at Perth.
The FDR (flight data recorder), the CVR (cockpit voice recorder) and the ADIRU (air data inertial reference unit) were removed from the plane, for a detailed examination. Under the supervision of the American NTSB, the ADIRU was shipped to its manufacturer for detailed analysis.
The FDR data confirmed the erroneous acceleration values had been displayed on the PFDs, as the pilots reported. The ADIRU produced those erroneous acceleration values and they were used by the PFC (primary flight computer). As it was designed to do, the PFC compared the information from the ADIRU, to the information coming from the SAARU (Standby Air Data and Attitude Reference Unit). That comparison ability enabled the PFC to reduce the severity of the initial pitching motion of the aircraft.
Chiaramente tutto cio' non ha
per il momento attinenza con quanto accaduto sull AF447 ma e' solo uno spunto di riflessione.
Ci sedemmo dalla parte del torto visto che tutti gli altri posti erano occupati.
(interno)
ci siamo persi anche un New Zealand ?
Non ci credo molto, sai?
