[A380] 空客关于飞机在滑行阶段出现Landing MEMO信息的解释。

Flight Warning Computer (FWC) – LDG INHIBIT memo displayed on ground before T.O.

ATA                      3153

AC Type                A318,A319,A320,A321

Description

Operators might report that A/C experienced display of LDG INHIBIT magenta memo on ECAM on ground before T.O. As per FCOM 1.31.15 , it should come up in FP 7 and 8 . What are Airbus advice regarding this memo occurrence?

Reference

SIL 34-084-ERRATIC AIRSPEED INDICATION – PITOT PROBES MAINTENANCE ACTION

Solution

According to ESLD FWC standard page 2.0.320 , this office confirms that LDG INHIBIT memo is displayed either into flight phase 7 or 8 when there is no flight phase inhibition overridden. Furthermore, we remind the airline that on ground the aircraft is into flight phase 2 when there is at least one engine running (not in T/O power) and aircraft speed is below 80 kts.

Please find hereafter a sum up of flight phase 7 and 8 triggering conditions:

-          Flight phase 7 is triggered while the aircraft is not on ground but below 800 ft, provide that both radio altimeters are operating and no immediate ground detected.

-          Flight phase 8 is triggered when aircraft is on ground, engine 1 or 2 running (not in T/O power) and aircraft speed below than 80 kts .

Airbus assumes that a wrong FWC flight phase computation could have led to the display of LDG INHIBIT memo. Indeed, it might be possible that FWC has computed spuriously flight phase 7 or 8 due to an erroneous data. Airbus would like to inform the airline that some operators have already reported such misbehavior in the past.

1/ it could happen that humidity, reflection or radio altimeters fluctuation disrupts data acquiring. Then if the altitude computed and provided to the FWC is not equal to a ground value, flight phase 7 will be unduly triggered instead of flight phase 2. In that case, it will be possible to generate the LDG INHIBIT memo. Generally, water located into the antenna is the root cause of these disruptions related to radio altimeters. Therefore, we recommend the airline to verify that there is no humidity trace infiltrated into RA antennas in case of reoccurrence.

2/ furthermore, FWC may confuse flight phase 2 and 8 whether the Boolean speed value is corrupted. Therefore, the FWC will generate a flight phase 8 instead of 2, enabling the triggering of the LDG INHIBIT memo. The assumption that could explained an airspeed up to 80 kts, while A/C stopped on ground, is a pressure trapped in the tube by water ingress. Moreover, on ground when the aircraft is stopped the computed airspeed is set to “No Computed Data” as long as the speed is lower than 30 kts. If an airspeed up to 80 kts was experienced during the event, this airspeed should have been observed on PFD Capt and F/O.

Regarding the airspeed generated by ADR 3 (not displayed), only an existing airspeed on dedicated stand-by instrument could have been noticed. In case of reoccurrence, Airbus recommends to perform the following AMM Tasks as a trouble shooting procedure (note that airline can also refer to SIL 34-084):

-          34-11-15-200-001 Inspection/Check of the Pitot Probe (9DA1, 9DA2, 9DA3)

-          34-10-00-170-001 Flushing of the Principal Total Pressure Lines

-          34-10-00-170-003 Draining and Flushing of Standby Pneumatic Circuits