UNRELIABLE SPEED INDIC/ADR CHECK PROC
Ident.: PRO-ABN-34-00012555.0002001 / 17 MAR 11
Unreliable speed indication may be due to radome damage, or due to air probe failure or
obstruction.
The indicated altitude may also be affected, if static probes are affected.
Unreliable speed cannot be detected by the ADIRU. The flight control and flight guidance
computers normally reject erroneous speed/altitude source(s), provided a significant difference is
detected.
However, they will not be able to reject two erroneous speeds or altitudes that synchronously
and similarly drift away. In this remote case, the aircraft systems will consider the remaining
correct source as being faulty and will reject it. Consequently, the flight control and flight guidance
computers will use the remaining two wrong ADRs for their computation.
Therefore, in all cases of unreliable speed, the pilots must identify the faulty ADR(s) and then
switch it (them) OFF.
If all ADRs provide unreliable data:
‐ Below FL250: Switch OFF the 3 ADRs to display the Backup Speed Scale (BUSS) and fly the
green area of the speed scale.
‐ Above FL250: Keep one ADR ON to prevent the display of the BUSS, and fly the aircraft using
the Pitch/Thrust tables.
Unreliable speed indications may be suspected, either by:
‐ Speed discrepancies (between ADR 1, 2, 3, and standby instruments).
‐ Fluctuating or unexpected increase/decrease/steady indicated speed, or pressure altitude.
‐ Abnormal correlation of the basic flight parameters (speed, pitch attitude, thrust, climb rate).
‐ Abnormal AP/FD/ATHR behavior.
‐ STALL warning, or OVERSPEED warnings, that contradicts with at least one of the indicated
speeds.
• Rely on the stall warning that could be triggered in alternate or direct law. It is not affected by
unreliable speeds, because it is based on angle of attack.
• Depending on the failure, the OVERSPEED warning may be false or justified. Buffet,
associated with the OVERSPEED VFE warning, is a symptom of a real overspeed condition.
‐ Inconsistency between radio altitude and pressure altitude.
‐ Reduction in aerodynamic noise with increasing speed, or increase in aerodynamic noise with
decreasing speed.
‐ Impossibility of extending the landing gear by the normal landing gear control.
UNRELIABLE SPEED INDICATION/ADR CHECK PROC
Ident.: PRO-ABN-34-H-00011949.0002001 / 04 MAY 12
If the safe conduct of the flight is impacted:
MEMORY ITEMS:
AP/FD.................................................................................................................................... OFF
A/THR.................................................................................................................................... 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.
GPS ALTITUDE................................................................................................ Display on MCDU