Typically at 80 kt IAS or when IAS fluctuations occur, whichever come first, the thrust-reverser levers are returned to the reverse idle position (then to the stow position, when reaching taxi speed).
As a result, the wheel-brakes’ contribution (purple curve) increases in order to maintain
Forward Idle
the desired deceleration rate (autobrake
Airspeed ( kt )
Figure 3
Stopping Forces Distribution
(Typical)
demand) until the pilot takes over with pedal braking.
This generic sequence of events is applicable to any aircraft equipped with ground spoilers, autobrake and thrust reversers.
Optimum Use of Braking Devices
Page 4
How do Ground Spoilers, Thrust Reversers and Brakes Contribute to Stop the Aircraft?
Figure 4 illustrates the respective contributions of the different braking devices to the total stopping energy, as a function of the achieved or desired stopping distance.
Figure 4 provides the following information:
.
For a given braking mode (i.e., pedal braking or autobrake mode):
. Achieved stopping distance ( landing roll );
.
For a desired or required stopping distance:
. Required type of braking (e.g., pedal braking or autobrake mode).
Max Landing Weight - Sea Level - ISA - Dry runway
% of Total Stopping Energy
1000 2000 3000 4000 Stopping Distance (m)
Figure 4 Stopping Energy Distribution versus Stopping Distance
(Typical)
Optimum Use of Braking Devices
Page 5
Factors Affecting Optimum Braking
The following factors often are involved in runway excursions (i.e., aircraft veering off the runway or taxiway), or in runway overruns:
.
Failure to arm ground spoilers, with thrust reversers deactivated (e.g., reliance on thrust reverser signal for ground spoilers extension);
.
Failure to use any braking devices (i.e., use of the inappropriate nose high “aerodynamic braking” technique);
.
Asymmetric thrust (i.e. one engine being above idle level in forward thrust or one engine failing to go into reverse thrust);
.
Brake unit inoperative (i.e., brake unit reported as “cold brake” for several flights, without corresponding MEL entry);
.
Anti-skid tachometer malfunction;
.
Absence of switching or late switching from NORM braking to ALTN braking or to emergency braking in case of abnormal braking;
.
Late selection of thrust reversers;
.
Absence of takeover or late takeover from autobrake, when required;
.
Inadequate crosswind landing technique; and,
.
Incorrect differential braking technique.
Operational Guidelines and Key Points
Strict adherence to the following operational standards and guidelines ensures optimum braking during the landing roll:
.
Arm ground spoilers;
.
Arm autobrake with the most appropriate mode for prevailing conditions (short runway, runway with downhill slope, low visibility, contaminated runway);
.
Select thrust reversers as soon as possible with maximum reverse thrust ( this increases safety on dry and wet runway, and is mandatory on runway contaminated with standing water, slush, snow or ice );
.
Monitor and call ground spoilers extension;
.
Monitor and call autobrake operation;
.
Be ready to take over from autobrake, if required;
.
Monitor engine operation in reverse thrust (e.g., increasing EGT and/or evidence of surge);
.
Monitor airspeed indication and return reverse levers to the reverse idle position at the published indicated airspeed or when airspeed fluctuations occur, whichever come first;
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