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on the training and operating experience of their flight crews.
One of the commonly used runway descriptors is coefficient of friction. Ground
friction measuring vehicles typically measure this coefficient of friction. Much
work has been done in the aviation industry to correlate the friction reading from
these ground friction measuring vehicles to airplane performance. Use of ground
friction vehicles raises the following concerns:
• the measured coefficient of friction depends on the type of ground friction
measuring vehicle used. There is not a method, accepted worldwide, for
correlating the friction measurements from the different friction
measuring vehicles to each other, or to the airplane's braking capability.
• most testing to date, which compares ground friction vehicle performance
to airplane performance, has been done at relatively low speeds (100
knots or less). The critical part of the airplane's deceleration
characteristics is typically at higher speeds (120 to 150 knots).
October 31, 2004
767 Flight Crew Training Manual
Landing
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 6.25
• ground friction vehicles often provide unreliable readings when
measurements are taken with standing water, slush or snow on the
runway. Ground friction vehicles might not hydroplane (aquaplane) when
taking a measurement while the airplane may hydroplane (aquaplane). In
this case, the ground friction vehicles would provide an optimistic reading
of the runway's friction capability. The other possibility is the ground
friction vehicles might hydroplane (aquaplane) when the airplane would
not, this would provide an overly pessimistic reading of the runway's
friction capability. Accordingly, friction readings from the ground friction
vehicles may not be representative of the airplane's capability in
hydroplaning conditions.
• ground friction vehicles measure the friction of the runway at a specific
time and location. The actual runway coefficient of friction may change
with changing atmospheric conditions such as temperature variations,
precipitation etc. Also, the runway condition changes as more operations
are performed.
The friction readings from ground friction measuring vehicles do supply an
additional piece of information for the pilot to evaluate when considering runway
conditions for landing. Crews should evaluate these readings in conjunction with
the PIREPS (pilot reports) and the physical description of the runway (snow,
slush, ice etc.) when planning the landing. Special care should be taken in
evaluating all the information available when braking action is reported as POOR
or if slush/standing water is present on the runway.
October 31, 2004
767 Flight Crew Training Manual
Landing
Copyright © The Boeing Company. See title page for details.
6.26 FCT 767 (TM)
Factors Affecting Landing Distance (Typical)
Proper
Improper
• Verify speedbrake extension
• Apply braking and reverse thrust
simultaneously
• Maintain steady full brake pedal
pressure
• Normal flare and touchdown
Stop
50'
Overextended flare
(3 sec. float after flare)
High approach speed
(+10 knots)
Maximum effort stop
Flaps 30
*Landing distance varies with runway condition, wet or dry.
Increase in typical landing distance
due to improper landing techniques
1/2 brake pressure
High over threshold
Speedbrakes not extended
Speedbrakes not extended & thrust
reversers not deployed
950'
760'-1400' *
300'-400' *
•
•
•
•
•
•
(100' alt.)
Data excludes contaminated runway considerations.
1200'-2800' *
1000'-1440' *
•
•
650'-780'
October 31, 2004
767 Flight Crew Training Manual
Landing
Copyright © The Boeing Company. See title page for details.
FCT 767 (TM) 6.27
Wheel Brakes
Braking force is proportional to the force of the tires on the runway and the
coefficient of friction between the tires and the runway. The contact area normally
changes little during the braking cycle. The perpendicular force comes from
airplane weight and any downward aerodynamic force such as speedbrakes.
The coefficient of friction depends on the tire condition and runway surface, (e.g.
concrete, asphalt, dry, wet or icy).
Automatic Brakes
Boeing recommends that whenever runway limited, using higher than normal
approach speeds, landing on slippery runways or landing in a crosswind, the
　
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