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you to identify the point on the
runway which is 40% of EDA
from the start of takeoff as a
check against acceleration. If .85
V2 has been achieved by this
marker, continue the take-off,
rotating at .9 V2. V2 should be
achieved by 50 feet. If you can't
get that, then the take-off should
be abandoned, keeping the
nosewheel in contact with the
runway, the throttles closed and
114 Operational Flying
maximum (safe) braking applied.
The maximum depth of slush or
water for landing should not
exceed 3mm, with limitations
for snow being the same as for
take-off.
Touchdown should be made
firmly and at the beginning of
the touchdown zone, the
nosewheel lowered as early as
possible, and any retarding
devices such as spoilers, lift
dump or reverse thrust used
before applying the brakes, to
give the wheels time to spin up.
Maximum anti-skid systems
should be used immediately.
Crosswind components should
be well below the normal dry
runway figure. However, release
the brakes if you have difficulty
steering, as anti-skid will reduce
cornering forces for directional
control.
Also, allow the engines to spool
down when changing from
reverse thrust to forward idle, or
they will transition to forward
thrust at a higher setting.
Runway Braking Action
Critical fluid depths for
aquaplaning can vary from
approx 0.1 to 0.4 of an inch,
depending on the surface. The
effects of water or liquids on a
runway that may affect braking
action are:
Condition Description
Damp Surface colour changed due to
moisture.
Wet Surface soaked, no significant
standing water visible.
Water Patches Significant standing water
patches visible.
Flooded Extensive standing water
patches visible.
Sandstorms
To be avoided. On the ground,
aircraft should be under cover, or at
least have engine blanks and cockpit
covers fitted, as well as those for
system and instrument intakes and
probes. These should be carefully
removed before flight so
accumulations of dust are not
deposited in the places the covers
are designed to protect. The stuff
gets everywhere!
Volcanic Ash
Flight through this can cause
abrasion to all forward facing parts
of aircraft, enough to impair
visibility through the windshields
and severely damage aerofoil and
control surface leading edges.
Airspeed indications may also be
completely unreliable through
blocking of pitot heads, and engines
may become choked and shut down.
Known areas of ash-producing
volcanic activity are found in
NOTAMs, as deduced with the help
of a Cray computer. Flight into them
should be avoided, particularly at
night or in IMC when ash clouds
won't be seen—don't expect weather
radar to help. If you end up in one,
the immediate action is to keep all or
some of the engines running and
find the shortest route out, which
may be downwards.
Mountain Waves
Where a high mountain range exists
with an airflow greater than 20 knots
over it in stable conditions, standing
waves may exist downwind,
noticeable by turbulence and strong
persistent up and down draughts.
Waves form in the lee of mountains
when a strong wind (over 20 kts) is
Operational Procedures 115
blowing broadside on (within about
30°). They are usually standing
waves, with several miles between
peaks and troughs, extending 10 or
20 000 feet above the range and up
to 200 or 300 miles downwind,
although the effects, such as
turbulence and strong up & down
draughts reduce with height. At
normal cruise altitudes, mountain
waves are usually free from clear-air
turbulence, unless associated with
jet-streams or thunderstorms.
Watch out for long-term variations
in speed and pitch attitude in level
cruise (the variations may be large).
Use the autopilot height-lock to
maintain altitude, but change power
as well. Bear in mind that at cruise
height the margin between low and
high speed limits can be relatively
small. Near the ground in a
mountain wave area, severe
turbulence and windshear may be
encountered. This region is known
as a lee wave rotor, and is caused by
flow separation behind the mountain
range (see also Mountain Flying).
Take-off or landing should not be
attempted. The quickest way out of
severe turbulence is up, with the
next best directly away from the
　
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