飞行员操作飞行手册Pilot Operational Flying Manual

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picked up on take-off could stop the

landing gear from operating,

amongst other things.

Zero degrees is actually when water

becomes supercooled and capable of

freezing. Airframe icing happens

when supercooled water droplets

strike an airframe below that. Some

of the droplet freezes on impact,

releasing latent heat and warming the

remainder which then flows back,

turning into clear ice, which can

gather without noticeable vibration.

On the ground this can mean

ground resonance in a helicopter,

and bits of ice flying off rotor blades

or propellers. In flight, the extra

weight and drag could cause descent

and improper operation of flying

controls. So—it's a good idea to

avoid icing conditions but, in any

case, you shouldn't go if you haven't

got the equipment, which naturally

must be serviceable (see Certification

for Flight in Icing Conditions, above).

The trend now is towards a "clean

air concept" which, essentially,

means that nothing should be on the

outside of an aircraft that should not

be there, except, of course for

deicing fluid.

All ice should be removed from

critical areas before take-off,

including hoar frost on the fuselage,

because even a bad paint job will

increase drag, which is relevant if

you're heavy, and hoar frost will

have a similar effect. Deicing details

should be entered in the relevant

part of the Tech Log, including

start/end times, etc. The critical

areas include control surfaces,

rotors, stabilisers and the like.

The ability of an object to

accumulate ice is known as its catch

efficiency; a sharp-edged object is

better at it than a blunt-edged one,

due to its lesser deflection of air.

Speed is also a factor. Due to the

speed and geometry of a helicopter's

main rotor blades, their catch

efficiency is greater than that of the

fuselage, so ice on the outside of the

cabin doesn't relate to what you

might have on the blades. In fact,

Canadian Armed Forces tests show

that you can pick up a lethal load of

ice on a Kiowa (206) rotor blade

inside 1-6 minutes, although it’s true

to say that 206 blades, being fairly

crude, don’t catch as much as more

sophisticated ones, such as those on

the 407. Mind you, tailplanes have

sharper leading edges than wings,

and will collect ice more efficiently,

so you might see nothing on the

wing yet have it on the horizontal

stabiliser. Because of the ratio of ice

thickness to the chord length, the

effects will be more marked.

It’s the rate of accretion that's

important, not the characteristics of

the icing, although clear ice is

definitely worse than rime ice, since

the latter contains air bubbles and is

much lighter and slower to build. It

also builds forward from the leading

Operational Procedures 109

edge as opposed to spreading

backwards. Variations on clear ice

are freezing rain and freezing drizzle,

both of which have larger droplets

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and are caused by rain, snow or ice

crystals falling through a layer of

warmer air at lower altitudes.

However, the latter’s droplets have a

much higher water content.

Although aircraft are different,

expect icing to occur (in the engine

intake area, anyway) whenever the

OAT is below 4o C. Otherwise, it can

form in clear air when humidity is

high. Clear ice is found most often

in cumulus clouds and unstable

conditions between 0 and –10 degs

C, and rime ice in stratiform clouds

between –10and –20.

Pitot head, static vent and fuel vent

heaters should be on whenever you

encounter icing, together with

anything else you feel is appropriate.

Try not to use deicing boots until at

least ½ inch of solid (not slushy) ice

has formed, otherwise they will

merely stretch the ice covering and

operate inside the resulting cocoon.

Waiting a while at least gives you the

ability to crack the ice off. I know

that some experts have determined

that this is not the case, but, trust

me, they’re wrong. If you operate the

boots too early, the ice coating on

them will merely flake and stay stuck

on. Boots on horizontal stabilizers,

by the way, will be less effective due

to their geometry.

You need warmer air to get rid of ice

effectively – just flying in clear air

can take hours, but I suppose you

could at least say you won’t get any

more. Climbing out is often not

possible, due to lack of performance

or ATC considerations, and

descending has problems, too – if

you’re getting clear ice, it’s a fair bet

that the air is warmer above you,

since it may be freezing rain, which

means an inversion, probably within

1000 feet or so, as you might get

before a warm front. In this

position, landing on your first

attempt becomes more important as

you are unlikely to survive a goaround without picking up more of

the stuff. You basically have three

choices, go up, down or back the

way you came. Going up is a good

first choice if you know the tops are

nearby, if only because you won’t

have a chance to do so later, but you

do present more of the airframe to

icing risk, which is why there is often

a minimum speed for climbing in

icing conditions.

Before going, check the freezing

level is well above minimum

altitudes, which will help get rid of

ice in the descent. Try to make sure

the cloud tops are within reach as

well, or you have plenty of holes.

Turbulence

This also exists high up, not so much

due to convection, but the passage

of fronts or mountain waves. You

can’t see the evidence of its existence

as there is little moisture to form

cloud, hence Clear Air Turbulence.

If turbulence is likely, mention it to

the cabin crew and advise the

passengers to return to, and/or

remain in their seats, ensuring their

seat belts/harnesses are securely

fastened. Catering and other loose

equipment should be stowed and

secured until the risk has passed. Fly

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at recommended turbulence speed.

110 Operational Flying

Windshear

This concerns airspeed changes over

about 10 kts resulting from sudden

horizontal or vertical changes in

wind velocity—more severe

examples will change not only

airspeed, but vertical speed and

aircraft attitude as well. Officially, it

becomes dangerous when the

variations cause enough

displacement from your flight path

for substantial corrective action;

severe windshear is considered to

cause airspeed changes of greater

than 15 kts, or vertical speed

changes greater than 500 feet per

minute. Expect it to occur mostly

inside 1000 feet agl.

Although mostly associated with

thunderstorms (see above), where

you have the unpredictability of

microbursts to contend with, it's also

present with wake vortices,

temperature inversions, mountain

waves and the passage of fronts, and

can occur over any size of area. You

can even get it where rain is falling

from a cumulus cloud, as the air is

getting dense from the cooling, and

will therefore fall quicker. It's not

restricted to aeroplanes, either—

helicopters can suffer from it above

and below tree top level in forest

clearings, when a backlash effect can

convert headwind to tailwind.

All fronts are zones of windshear—

the greater the temperature

difference across them, the greater

the changes will be. Warm fronts

tend to have less windshear than

cold ones, but as they're slower

moving, you catch it for longer. In

general, the faster the front moves,

the more vigorous the weather

associated with it; if it goes slower,

the visibility will be worse, but you

can still get windshear even then and

always for up to an hour after its

passage.

One significant effect of windshear

is, of course, loss of airspeed at a

critical moment, similar to an effect

in mountain flying, where a wind

reversal could result in none at all!

You would typically get this from a

downburst out of a convective type

cloud, where initially you get an

increase in airspeed from the extra

headwind, but if you don’t anticipate

the reverse to happen as you get to

the other side of the downburst, you

will not be in a position to cope with

the resulting loss. This has led to the

classification of windshear as either

performance increasing or performance

decreasing. Windshear encountered

near the ground (say below 1000

feet) is the most critical, mainly

because you can't quickly build up

airspeed—remember the old saying;

altitude is money in the bank, but

speed is money in the pocket.

The effects also depend on the

aircraft and its situation, in that

propeller driven types suffer less

than jets, and light aircraft tend to be

less vulnerable than heavy ones—

those with a good power to weight

ratio will come off best. The take-off

leaves you most vulnerable because

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of the small scope for energy

conversion, less amounts of excess

engine power and the amount of

drag from the gear and flaps, which

is not to say that landing is that

much better.

In extremely simple terms, where

windshear is expected, you should

have a little extra airspeed in hand;

you can help with the following:

Operational Procedures 111

· On take-off, use the longest

runway, less flap and more

airspeed up to about 1000 feet

agl, but watch your gradient and

use about 10 kts more than

usual. If shear is indicated by

rapidly fluctuating airspeed

and/or rate of climb or descent,

apply full power and aim to

achieve maximum lift and

distance from the ground. Be

prepared to make relatively

harsh control movements and

power changes, using full

throttle if you have to—new

engines are cheaper than new

aircraft.

· In a jet, you can use higher

angles of attack and still get a

sizeable amount of lift for a

moderate increase in drag,

because the wings are designed

that way. Various methods are

used to inform you of the stall,

and you want to keep the thing

flying just above that point—

something that may require

some practice in a simulator.

Similarly, if the shear is

encountered during the

approach, positive application

of power and flying controls

should keep the speed and rate

of descent within normal limits;

if there is any doubt, abandon

the approach and take action as

above.

· Set the prop RPM to maximum

(for flat pitch).

Windshear should be reported to

ATC as soon as possible, for the

benefit of others. It can be detected

by radar, using Doppler Shift to

calculate how fast raindrops are

moving and subsequently the pattern

of air movement, specifically looking

for headwind/tailwind

combinations. In theory, this

technology could also be used to

detect turbulence at higher levels,

assuming raindrops are present.

Your Company has to provide a

formal windshear training program.

If they don’t, there is an FAA video

available from the CAA to AOC

holders only.

Jetstreams

These occur at the tropopause, or

the boundary between lower air

(troposphere) and the stratosophere,

where it collects and channels air

into a high-speed stream due to a

strong horizontal temperature

gradient. They lie to the North of

frontal systems where the

temperature gradient is greatest, and

are stronger in Winter. To qualify for

the name, the windspeed must be at

least 60 kts. A jetstream may only be

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a few hundred miles wide, but be

thousands of miles long. They have

extreme turbulence associated with

them, which can extend as much as

15000 feet below the tropopause,

usually on the polar side—also, head

wind components will naturally

increase your fuel consumption for

the trip. Bear in mind that the

tropopause lowers in Winter, which

will move the unstable air beneath

the jetstream further downwards as

well (it’s unstable because the

jetstream is sucking it up like a

vacuum).

Shallow fog

In shallow fog, you may be able to

see the whole of the approach

and/or runway lights from a

considerable distance, even though

112 Operational Flying

reports from the aerodrome indicate

fog. On descending into the fog

layer, your visual reference is likely

to drop rapidly, in extreme cases

from the full length of the runway

and approach lights to a very small

segment. This may give the

impression that you're pitching nose

up, making you more likely to hit the

ground after corrective movements.

You should be prepared for a missed

approach whenever you have the

slightest doubt about forward

visibility. The minimum RVR for

landing from a visual circuit is 800m.

Whiteout

Defined by the American

Meteorological Society as “An

atmospheric optical phenomenon of

the polar regions in which the

observer appears to be engulfed in a

uniformly white glow”. That is, you

can only see dark nearby objects –

no shadows, horizon or clouds, and

you lose your depth perception. It

occurs over unbroken snow cover

beneath a uniformly overcast sky,

when the light from both is about

the same. Blowing snow doesn’t

help. It’s particularly a problem if the

ground is rising. Once you suspect

whiteout, you should immediately

climb or level off towards an area

where you can see things properly.

Clear Air Turbulence

This can sometimes be avoided by

simply changing the cruising level.

Listen out for other aircraft reports.

Rain, Snow and Other Precipitation

On the ground, you may need slower

taxying speeds and higher power

settings to allow for reduction in

braking performance and the

increase in drag from snow, slush or

standing water, so watch your jet

blast or propeller slipstream doesn't

blow anything into nearby aircraft.

When taxying

Try not to collect snow and

slush on the airframe, don't taxi

directly behind other aircraft,

and take account of banks of

cleared snow and their proximity

to wing- and propeller-tips or

engine pods. Delay flap selection

to minimise the danger of

damage, or getting slush on their

retraction mechanisms.

On the runway

A contaminated runway has

significant amounts of standing

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water, ice, slush, snow or even

heavy frost along its surface.

The most important factors are

loss of friction when

decelerating, and displacement

of (and impingement drag when

accelerating through) whatever

is on it, so it may be difficult to

steer, and take-off and

accelerate-stop distances may be

increased due to slower

acceleration, as will landing

distance because of poor

braking action and aquaplaning,

which is a condition where the

built-up pressure of liquid under

the tyres at a certain speed will

equal the weight of the aircraft.

Higher speeds will lift the tyres

completely, leaving them in

contact with fluid alone, with

the consequent loss of traction,

so there may be a period during

which, if one of your engines

stops on take-off, you will be

unable to either continue or stop

within the remaining runway

length, and go water-skiing

Operational Procedures 113

merrily off the end (actually,

you're more likely to go off the

side, so choosing a longer

runway won't necessarily help).

The duration of this risk period

is variable, but will vary

according to your weight.

Reverted Rubber Hydroplaning

happens when a locked tyre

generates enough heat from

friction to cause the resulting

steam to lift the tyre off the

runway. The heat causes the

rubber to revert to its basic

chemical properties.

A rough speed at which

aquaplaning can occur is about 9

times the square root of your

tyre pressures, 100 pounds per

square inch therefore giving you

about 90 kts—if this is higher

than your expected take-off

speed you're naturally safer than

otherwise. The point to note is

that if you start aquaplaning

above the critical speed (for

example, when landing), you can

expect the process to continue

below it, that is, you will slide

around to well below the speed

you would have expected it to

start if you were taking off.

Most factors that will assist you

under these circumstances are

directly under your control, and

it's even more important to

arrive for a "positive" landing at

the required 50 feet above the

threshold at the recommended

speed on the recommended

glideslope than for normal

situations. Under-inflating tyres

doesn't help—each 2 or 3 lbs

below proper pressure will lower

the aquaplaning speed by 1 knot,

so be careful if you've descended

rapidly from a colder altitude.

Aquaplaning aside, it's obviously

a good idea to avoid using a

contaminated runway, but if this

isn't possible, there are

techniques that may assist you to

reach a speed at which you can

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continue if an of engine fails, or

stop in the shortest practicable

distance, which will include not

taking off with a tailwind

component or carrying

unnecessary fuel. The

recommended maximum depth

of slush or water for take-off

should not exceed 15mm, and of

dry snow 60mm. Wet snow

should be treated as slush.

The airfield must have either a

paved runway having an

Emergency Distance Available

of not less than 1½ x TODR

(say a PA23) or 2 x TODR (an

AA5) or 1500 feet, whichever is

the greater; or a grass runway

having an Emergency Distance

Available of not less than 2 x

TODR (PA23) or 2.66 x TODR

(AA5) or 2000 feet, whichever is

the greater. The minimum

cleared width should be 70 feet

(see Performance for definitions).

There should be provision for

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.

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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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range. Fly parallel to the range in an

updraught, avoiding peaks.

Significant Temperature Inversions

Performance is affected by variations

in temperature, and inversions will

do so adversely. Large ones

encountered shortly after take-off

can seriously degrade climb

performance, particularly when

heavy. Even a small inversion in the

upper levels can prevent you

reaching a preferred cruising altitude.

At lower levels, expect deteriorating

visibility, as an inversion can prevent

fog clearance for prolonged periods.

Another good reason for avoiding

the top of an inversion is that all the

industrial pollutants collect there,

especially in the stubble burning

season which may include

incinerated pesticides.

Wake Turbulence

A by-product of lift behind every

aircraft (including helicopters) in

forward flight, particularly severe

from heavy ones. Wake vortices are

horizontally concentrated whirlwinds

streaming from the wingtips, from

the separation point between high

pressure below and low pressure

above the wing. The heavier and

slower the aircraft, the more severe

they will be, and flaps, etc. will only

have a small effect in breaking them

up. The effects become undetectable

after a time, varying from a few

seconds to a few minutes after the

departure or arrival, although they

have been detected at 20 minutes.

Vortices are most hazardous to other

aircraft during take-off, initial climb,

final approach and landing.

Although there is a danger of

shockloading, the biggest problem is

loss of control near the ground. You

are safest if you keep above the

approach and take-off path of the

other aircraft, but, for general

purposes, allow at least 3 minutes

behind any greater than the Light

category for the effects to disappear

(but see the table below).

Wake generation begins when the

nosewheel lifts off on take-off and

continues until it touches down

again after landing. Vortices will drift

downwind, at about 400-500 fpm for

larger aircraft, levelling out at about

900 feet below the altitude at which

they were generated. Eventually they

116 Operational Flying

expand to occupy an oval area about

1 wingspan high and 2 wide. Those

from large aircraft tend to move

away from one another so, on a calm

day, the runway itself will remain

free, depending on how near the

runway edge the offending wings

were. They will also drift with wind,

so your landings and take-offs

should occur upwind of moving

heavy aircraft and before the point

of its take-off and after the point of

landing. Although ATC will

normally suggest an interval, use

these tables as a guide:

Successive aircraft on finals

Although ATC will normally suggest

an interval, the table below can be

used as a guide, although there is

never a guarantee you will not

encounter wake turbulence,

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whatever separations are given:

Leading

Aircraft

Following

Aircraft

Min dist

(miles)

Heavy Heavy 4

Medium 5

Small 6

Light 8

Medium Medium* 3

Small 4

Light 6

Small Med or Small 3

Light 4

Note: If the leading medium is a B757, increase

to 4 miles, as they are difficult to slow down and

lose height with, and often fly steeper

approaches. BV234, Puma, Super Puma, EH

101 and S61N helicopters are Small. Bell 212,

Sikorsky S76 and smaller machines are Light.

Departing aircraft

Applies to IFR and VFR flights.

Same or parallel runways less than

760m apart (inc grass)

Leading Follow Departing From Min space

Heavy Med/Sm/Lt Same takeoff

posn

2 mins

Medium/Small Light Same takeoff

posn

2 mins

Heavy Med/Sm/ Lt Intermediate

posn

3 mins

Medium/Small Light Intermediate

posn

3 mins

Runways with displaced landing

thresholds where flight paths cross

Leadiing Following Min space

Heavy Arrival Med/Small/Light Dep 2 mins

Heavy Departure Med/Small/Light Arr 2 mins

Medium Arrival Light/Small Dep 2 mins

Medium Departure Light/Small Arr 2 mins

Crossing and diverging or parallel

runways over 760m apart

Lead Crossing Behind Min Dist Time Equiv

Hvy Hvy/Med/Sm/Lt 4/5/6/8 m 2/3/3/4 m

Med Med/Sm/Lt 3/4/6 miles 2/2/3 mins

Small Med or Sm/Lt ¾ miles 2/2 mins

Opposite direction runways

There should be at least 2 minutes

between a light, small or medium

and a heavy, and between light and a

small or medium within 760 m (a

grass strip is a runway).

Helicopters

Rotor downwash is wake

turbulence from helicopters,

which is easy to forget when

hovering near a runway

threshold or parked aircraft with

little wind. Downwash also

creates dust storms and can lift

even heavy objects into the air,

instantly presenting Foreign

Object Damage (FOD) hazards

to engines, main and tail rotor

blades (so don't bolt your FOD,

it gives you ingestion!—old RAF

joke, on which I hope there's no

Operational Procedures 117

copyright). Plastic bags or

packaging sheets are FOD, too.

Generally speaking, the larger

the helicopter, the greater the

potential danger (obvious,

really). Still air conditions permit