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UNRELIABLE SPEED INDICATION

FOR TRAINING ONLY. DO NOT USE FOR FLIGHT!


AIR DATA INERTIAL REFERENCE SYSTEM  DESCRIPTION


The Air Data and Inertial Reference System (ADIRS ) supplies temperature, anemometric, barometric and inertial parameters to the EFIS system (PFD and ND ) and to other user systems (FMGC,FADEC,ELAC,SEC,FAC,FWC,SFCC,ATC,GPWS,CFDIU,CPC).


The system includes:


‐ Three identical ADIRUs (Air Data and Inertial Reference Units).

Each ADIRU is divided in two parts, either of which can work separately in case of failure in the other:

• The ADR part (Air Data Reference) which supplies barometric altitude, airspeed, Mach, angle of attack, temperature and overspeed warnings.

• The IR part (Inertial Reference) which supplies attitude, flight path vector, track, heading, accelerations, angular rates, ground speed and aircraft position.

‐ One ADIRS control panel on the overhead panel for selection of modes (NAV , ATT, OFF) and indications of failures.

‐ Four types of sensors:

• Pitot probes (3)

• Static pressure probes (STAT) (6)

• Angle of attack sensors (AOA) (3)

• Total air temperature probes (TAT) (2)


These sensors are electrically heated to prevent from icing up.

‐ Eight ADM s (Air Data Modules) which convert pneumatic data from PITOT and STAT probes into numerical data for the ADIRUs.

‐ A switching facility for selecting ADR 3 or IR 3 for instrument displays in case of ADIRU1 or 2 failure.

UNRELIABLE AIRSPEED – MEMORY ITEMS

If you ever find yourself in a situation that you are finding hard to understand and have lost your situational awareness you need to default back to the Airbus Golden Rules.


1. Fly, Navigate & Communicate in this order and with appropriate task sharing

2. Use the appropriate level of automation at all times

3. Understand the FMA at all times

4. Take action if things do not go as expected


These memory items are to be applied if the safe conduct of the flight is impacted.


  • PF Announce………………………………….”UNRELIABLE SPEED”

  • AP……………………………………………………………………….. OFF

  • A/THR………………………………………………………………….. OFF

  • FD……………………………………………………………………….. OFF

PITCH/THRUST:


  • Below THRUST RED ALT……………………………………15° / TOGA

  • Above THRUST RED ALT and Below FL 100………….. 10° / CLB

  • Above THRUST RED ALT and Above FL 100……………..5° / CLB

  • FLAPS (if CONF 0(1)(2)(3))……….. MAINTAIN CURRENT CONF

  • FLAPS (if CONF FULL)…… SELECT CONF 3 AND MAINTAIN

  • SPEEDBRAKES…………………………CHECK RETRACTED

  • L/G………………………………………………………………. UP

When at, or above MSA or Circuit Altitude: Level off for troubleshooting.

To level off:

AP…………………………………………………………………………………….OFF A/THR……………………………………………………………………………….OFF FD……………………………………………………………………………………OFF SPEEDBRAKES………………………………………………CHECK RETRACTED PITCH/THRUST TABLE……………………………………………………..APPLY

It should be highlighted that if you experience unreliable speed indications during cruise flight then you should NOT set 5o and CLB power immediately. Simply maintaining your current pitch attitude, if the aircraft is straight and level, would be the correct response.

When flight path is stabilized:


AP…………………………………………………………………………………..OFF A/THR………………………………………………………………………….OFF FD………………………………………………………………………………….OFF

SPEEDBRAKES……………………………………CHECK RETRACTED

FLIGHT PATH……………………………………………KEEP STABILIZED


RESPECT STALL WARNING

AFFECTED ADR IDENTIFICATION


PROBE/WINDOW HEAT……………………………………………………..ON

ALL SPEED INDICATIONS…………………………………..CROSSCHECK

ADR 3 and STBY speeds use the data of the same probe.

– If at least one ADR confirmed reliable:

RELIABLE AIR DATA……………………………………………………USE

UNRELIABLE ADR pb(s)………………………………………………OFF

-If affected ADR(s) cannot be identified, or all ADRs affected:

KEEP ONE ADR ON

TWO ADR pbs……………………………………………………………..OFF

This prevents the flight control laws from using two coherent but unreliable ADR data.

FOR LANDING: USE FLAP 3

APP SPD ……………………………………………………………..VLS +10 kt

LDG DIST PROC……………………………………………………….. APPLY

Note: Refer to QRH charts for Pitch and Thrust values

BACKUP SPEED SCALE (BUSS)

The BackUp Speed Scale (BUSS) enables to fly the aircraft when airspeed indications are unreliable.

When the BUSS is activated:

‐ The BUSS replaces the normal speed,

‐ The GPS altitude replaces the barometric altitude scales.

The BUSS is displayed on both PFD s when the flight crew turn off all ADRs.

The activation of this BUSS is not reversible.

The BUSS information is based on the angle of attack (AOA), and depends on the slat/flap configuration.

(1) Red FAST area

This area indicates the excessive speed range while decreasing the margin to the maximum structural speed.

(2) Amber FAST area

This area indicates the excessive speed range while keeping an appropriate margin to the maximum structural speed.

(3) Green area

The green area indicates the safe speed range.

(4) Target speed (green triangle)

This symbol indicates the optimum target speed.

During the approach, it indicates the target speed for the approach.

(5) Actual speed reference (yellow line)

This line indicates the current speed of the aircraft.

(6) Amber SLOW area

This area indicates the too low-speed range while keeping an appropriate margin to the stall speed.

(7) Red SLOW area

This area indicates the too low-speed range while reducing the margin to the stall speed.

BACKUP ALTITUDE SCALE

(1) CurrentGPSaltitude

Two amber dashes cover the last two digits.

(2) GPS ALT flag

This flag indicates that the barometric altitude is replaced by the GPS altitude.

(3) The vertical speed indication is no longer displayed.

GENERAL NOTES

Analysis of the in-service events shows that:

The majority of unreliable speed events at low altitude are permanent situations; due to the obstruction of pitot probes by rain, severe icing, or foreign objects. At high altitude, typically above FL250, the cases of unreliable speed are mostly a temporary phenomenon: They are usually due to contamination of the pitots by water or ice, in specific meteorological conditions. In service experience shows that such a contamination typically disappears after a few minutes, allowing recovery of normal speed indications.

The PF adjusts the pitch and thrust to maintain the AOA in the green area of the speed scale. For approach, the flight crew should perform a stabilised approach. The flight crew should change the aircraft configuration with wings level.

To retract/extend flaps, apply the following technique:

• Before retracting the next flaps configuration, fly the upper part of the green band.

• Before extending the next flaps configuration, fly the lower part of the green band.

This technique limits the excursion in the amber zones when changing the flaps configuration.

CAUTION: When flying with the BUSS, do not use the speed brakes. Flying with speed brakes extended would affect the relationship between speed and AOA, and the BUSS would, therefore, provide erroneous data.

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