HEATHROW AIR TRAFFIC CONTROL

INSTRUCTION MANUAL

 1. Introduction
 2. Loading the game
 3. System description
    3.1. Radar screen
    3.2. Stack display
    3.3. Radio communication
 4. Demonstration Exercise in detail (exercise 5)
 5. Basic vectoring with Slow Traffic (exercise 1)
 6. Mixed traffic with Airspace restrictions (exercise 2)
 7. Landing interval and separation (exercise 3)
 6. Vortex spacing and outbound aircraft (exercise 4)
 9. Emergency traffic (exercise 6)
10. Potential disaster (exercise 7)
11. Summary sheet

1. INTRODUCTION

Congratulations - you are the proud owner of Heathrow Air Traffic
Control for the 16K or 48K ZX Spectrum, written entirely in machine
code for maximum enjoyment.

Your purchase will provide you with hours of fun because it simulates
as closely as possible the real-life operation of Air Traffic Control
Centre at London Heathrow Airport. You should not expect to
understand all the operations immediately - you must first learn the
meanings of special words and phrases like localiser, expedition,
glide slope and fully established.

To make the most of your cassette as soon as possible you are advised
to:
 (a) read all the instructions, particularly sections 3 and 4;
 (b) load the cassette and watch the demonstration (exercise 5);
 (c) re-read sections 3 and 4;
 (d) re-run exercise 5 and follow the description of it in section 4.

You should then be ready to progress through the various exercises.
Eventually you will become fully capable of dealing with any situation
and will be able to take charge of Heathrow Air Traffic Control.

The program is designed to simulate the functions of Heathrow 
Airport air traffic control. The objective is to land 8 aircraft (or as many
as possible within the time limit of 25 minutes) as safely as you can.
The task is a complex one and has been broken down into a number of
exercises to enable you to gradually develop your expertise.

2. LOADING THE PROGRAM

Load the program using the instructions LOAD "" on your ZX Spectrum
and press ENTER. Start the tape at the beginning and wait until you
are offered a menu of options on the TV screen, then switch off the
tape. The menu consists of a choice of several exercises.

3. SYSTEM DESCRIPTION

In order to understand the Air Traffic Control problem run the
demonstration exercise by either pressing 5 or leaving the computer
for 40 seconds, after which time the demonstration is selected
automatically.

Once into the demonstration the radar screen is displayed together
with information on the aircraft. The aircraft arrive at four holding
stacks which are radio beacons around which the aircraft fly in a
racetrack pattern. Air Traffic Control (ATC) then gives instructions to
position the aircraft onto a pair of radio beacons called the ILS
(Instrument Landing System) with which the aircraft can complete the
landing at Heathrow airport.

3.1.  Radar Screen

The radar screen is the dark rectangle with the four holding stacks
shown as small white signs around which the aircraft (shown as white
blocks with a trail of white dots) circle. The stacks represent
Bovingdon (BNN) on the top left, Lambourne (LAM) on the top right
Ockham (OCK) on the bottom left and Biggin (BIG) on the bottom
right. The small box on the top right corner represent Luton airport.

In the centre of the screen is a small box representing Heathrow and
on either side are shown the extended centrelines of the double
runways at Heathrow. The small dots on the centrelines are range
marks located every two miles (with a double dot at 10 miles). The
total length of the centreline is 15 miles either side. Heathrow has two
parallel runways, one for landing and one for take off.  We are
concerned only with the landing runway which is the top line. The
runway to the right of the box is the westerly landing direction since
aircraft are landing into a westerly wind and flying from right to left.
Conversely aircraft landing from left to right use the easterly landing
direction on the left of the box. In the demonstration a westerly
landing direction is used.

As the demonstration progresses the aircraft circle around the stacks.
Near each aircraft is a label produced by the Secondary Surveillance
Radar (SSR). This label consists of a one letter call sign of the aircraft
and one digit showing the altitude of the aircraft in thousands of feet,
eg A6 means aircraft A at 6000 feet. Labels are only displayed on
aircraft below 8000 feet and only inbound aircraft are controlled and
labelled. Outbound aircraft are marked with the altitude only.

3.2.  Stack Display

To the right of the radar screen is the stack display. This shows
information about each aircraft from the time it first appears on the
radar until it lands. It is divided into 4 sections (one on top of the
other), one for each of the four holding stacks (the appropriate 3 letter
designator being printed on the left). It is also divided into 3 vertical
columns, the left hand section contains aircraft identity (one capital
letter) followed by the aircraft type (one small letter) followed by the
level (altitude) to which it has been cleared by ATC. The aircraft type
can be one of four types:- h for heavy jet (such as Boeing 747), m for
medium jet (such as Trident), s for small propellor driven airliner (such
as Herald) and l for light aircraft (such as Navago).

The second vertical column contains the aircraft heading or other
direction information eg 'H' = Holding at stack, 'O/S' = aircraft
overshooting, 'loc' = localiser established, 'EST' = fully established.
Aircraft heading is the direction in which an aircraft is flying measured
in compass degrees ie 360 degrees = North, 270 degrees = West,
130 degrees = South East etc (direction on the radar screen is aligned
such that North points straight up). The third vertical column contains
the aircraft speed in nautical miles per hour (knots). When an aircraft
is less than 4 miles from touchdown no value will be displayed, as you
are not permitted to control the speed of an aircraft at that stage of the
approach. To assist in identifying items in the stack display the
columns are headed 'I' for identity, 'l' for level (altitude), 'hd' for
heading and 'sp' for speed. Below the stack display wind information
is given measured in compass degrees (the direction from which the
wind is blowing), followed by the speed in knots eg wind 240/20
means a wind from the south west at 20 knots.

3.3 Radio Communication

On the left hand side, below the radar screen in the equivalent to the
radio communication at Heathrow. You can send instructions to
aircraft using the keyboard. As you press each key the appropriate
symbol will appear. Instructions have the format:- aircraft identity (1
letter), instruction type (input the first letter and the whole word will
be printed), appropriate parameter (letter or numbers).

The instructions accepted are:-

Altitude - followed by one number, will instruct the aircraft to climb or
descend to the level ENTERed. (The number being the number of
thousands of feet eg A Altitude 3 means aircraft A climb or descend to
3000 feet). You may only input levels 2-9. 2000 feet is the lowest safe
level, 9000 feet is the top of your airspace.  Any error in this will give
the response "wrong lev" (wrong level). The rate at which an aircraft
will climb or descend depends upon the aircraft type, ie l/s aircraft
climb and descend slower than m/h aircraft.

Once an instruction has been typed in, press ENTER. If the instruction
is acceptable it will move down one line and the word "roger" will
appear after it meaning 'message received and understood'. If you
make a mistake and wish to retype the instruction prior to ENTERing,
press Key Z to delete the instruction.

"Left":- This is a heading change instruction telling an aircraft to turn
left to the heading designated after the word 'Left' eg A Left 240
means aircraft A to turn from its present heading onto heading 240
degrees with a left turn. It takes some practice to visualise whether a
turn is to the left or right, especially when aircraft are not flying 'up' the
radar screen. Any value of heading input will be rounded to the
nearest 10 degrees.

"Right":- a heading change instruction telling an aircraft to turn right
to the designated heading.

"Speed":- this tells an aircraft to adjust speed to the specified speed 
e.g. C Speed 200 means aircraft C adjust speed to 200 knots.

The different types of aircraft have different speed ranges over which
they may fly. If you input a speed not possible for that particular aircraft
or make some other error on entry you will get the response "wrong
spd" (wrong speed).

    aircraft types       maximum speed       minimum speed

         l                  180 kts             120 kts
         s                  210 kts             140 kts
         m                  250 kts             160 kts
         h                  250 kts             160 kts

Speeds when input are rounded down to the nearest even number.

"Quote":- this is an enquiry to an aircraft followed by one letter which
specifies the information that is required. The information appears in
the space normally occupied by the message 'roger'. The letter 'A'
returns a value of the aircraft altitude in thousands of feet e.g. A Quote
A might return a value 3.8 meaning aircraft A altitude = 3,800 feet.
The letter 'H' returns the aircraft heading, and 'S' the speed. If a letter
is input that is not recognised you will get the response "say again"
inviting you to re-input the enquiry with the correct letter.

If you get the response "not yours", this means that you have
addressed an aircraft that is not under your control (either not yet on
the radar, already landed or overshooting).

Below the space on the TV screen reserved for the instruction, is a line
awaiting any relevant messages. When massages come in they will
flash until acknowledged by pressing the "space" key.

Certain of the keys have special functions:-

"Space":- acknowledges incoming messages (you will get no further
messages until each message is acknowledged, in turn).

"Enter":- used for evaluating instructions.

"Z":- deletes the line of instruction currently being typed.

"V":- freezes the exercise and waits until key "W" is pressed.

"W":- resumes the exercise after holding or slows the rate to normal
game (6 seconds per update).

"M":- gives a page of events.

"Y":- accelerates the update rate to a rate faster than real time (you can
switch between the two rates using keys Y and W).

"X":- holds the exercise and displays a page of information containing
an assessment of your performance to date (based on average landing
interval, expedition, safety and if applicable, emergency handling -
you need 70% to pass).

Expedition marks are dependent upon 1) the time it takes to land the
first aircraft (the sooner the better); 2) the average landing interval (the
smaller the better) and 3) the number of aircraft landed (the more the
better).

Beneath the assessment is a series of pages of significant events. Key
"M" gives a new page of events, at the end of all events you are given
the prompt "Press R to restart, A for a new exercise" which are the
keys to return you to the exercise or start a new one.

4. DEMONSTRATION EXERCISE IN DETAIL

Re-run the demonstration exercise and try to follow the detailed
instructions appearing on the screen. These give an insight into the
ATC techniques employed. To help you follow the technique press key
'W' to slow the action or key 'V' to freeze the action.

The exercise starts with a completely empty radar screen and stack
display. Aircraft are introduced one at a time at levels 7 and 8 (7000
and 8000 feet) at each individual stack in turn (these levels are used
so that these aircraft are safely above any outbound aircraft which only
climb to 6000 feet). Before they appear on the radar they are
controlled by an en route controller, which also controls the outbound
traffic, until such time as they can safely be put into the holding stacks
at least 1000 feet above the next lowest aircraft.

The computer starts to input instructions to the aircraft, firstly "A Right
# 320" and enter this. This means A is given a heading to leave the
holding stack at 320 degrees (the aircraft is originally heading 300
degrees - a fact you can establish using a "Quote" instruction - thus
the aircraft turns right by 20 degrees). The next three instructions are
similar heading instructions, the computer is trying to achieve a
continuous flow of traffic (so as to be expeditious - ie land as many
aircraft as quickly as possible), thus it is planning to position F behind
A, B behind F and so on.

The next instruction is "B Speed # 180". This slows B down from
230 knots (as stated on the stack display as his present speed) to 180
knots to assist in positioning the aircraft behind F. "F Speed # 180" is
a similar instruction. The aircraft must be at 200 knots or slower to
successfully intercept the ILS, thus you have to slow up all 'h' and 'm'
aircraft for the reason as well.

Next "A altitude # 3" gives A a descent instruction from its present
level of 7000 to 3000 feet, to get the aircraft at or below the glide
slope when full establishment on the ILS is achieved, "B altitude # 7"
descends 'B' to the lowest altitude allowed and below aircraft 'G'
holding at 'OCK' so that if 'B' is not turned in time he will be safe from
collision with 'G'.

"A Speed # 200" reduces the speed of A to 200 knots in good time to
allow the speed of 'A' to reduce slowly to 200 to enable successful
establishment on the localiser. "P Left 120/Q Right 130" continues
the computer approach sequence plans by turning P and Q into the
flow of traffic. You will see, at this point, that a new aircraft 'C' has
been introduced at 'BIG' because it is now safe to do so.

The types of action so far discussed are continued throughout. Only
significant acts are mentioned from now on.

At 3 mins 42 secs "C Altitude # 7" descends C to the lowest safe
altitude available (although 'B' is still at 7 according to the stack
display, the computer will ensure that B and C remain radar separated
ie at least 3 miles apart). This helps when descending aircraft below
the glide path (the higher they start the longer it takes to descend
below it).

At 4 mins 0 secs "B Right # 70" positions B behind F. At 4 mins 18
secs" a Left # 310E" turns 'A' onto a heading from which it will
intercept the ILS (hence the 'E' on the end of the instruction - Note
that the heading is within the allowed range of runway heading plus or
minus 40 degrees).

At 5 mins 12 secs "F Left" 360 turns 'F' left onto a heading of 360
degrees (due North - incidentally the computer accepts "0" as North
also). This positions F behind A on what is termed as "base leg", a
heading roughly at right angles to the runway centre line. From this or
a similar heading it is relatively easy to judge when to turn an aircraft
onto a heading to intercept the ILS.

At 5 mins 30 secs, look at the stack display at aircraft A and you will
see the letters 'loc' showing that it is established on the localiser and
will turn to fly down the runway centre line. At 5 mins 48 secs at the
same place on the stack display are the letters 'EST' showing that A is
now established on the localiser and glide slope (note that with A at
3000 feet this has occurred at 10 miles from touchdown - ie a slope of
300 feet per mile).

At 6 mins 18 secs, F turned onto a heading to intercept the ILS.
Note that aircraft 'A' is 6 miles ahead of 'F' and as 'A' is a heavy
aircraft and 'F' is a medium aircraft type, 2 minutes vortex separation
is required for landing.

At 6 mins 30 secs "B Left # 0" turns 'B' onto a "base leg".

At 6 mins 48 secs "P left # 100" turns P left by 20 degrees to ensure
that at least 3 miles radar separation is maintained from aircraft 'F' and
'B' as they turn onto the ILS.

At 7 mins 30 secs "C Quote # H" is an enquiry about the heading of 'C'
to find out which of the 2 aircraft holding at 'BIG' is 'C'. The reply, 190
degrees shows that C is the aircraft on the right which is heading 190
degrees (you will notice that there are no labels at 'BIG' at this time -
this is because the labels are displayed above and to the right of the
relevant aircraft, and as 'C' is close to the edge of the screen no label
shows).

At 8 mins 48 secs "P Right # 180" turns P onto a 'base leg' from the
north of the runway centreline.

At 9 mins 12 secs "A LANDED safely" flashes at the bottom of the
screen, the blip disappears from the radar and the information is
blanked out on the stack display. The message is acknowledged at 9
mins 36 secs and hence stops flashing.

The exercise ceases at 10 mins and revert to the menu of options.

5. BASIC VECTORING, SLOW TRAFFIC - EXERCISE 2

In this exercise you are given all light aircraft and the objective is to
establish them on the ILS and get them to land.

There are two stages to establishing an aircraft (a/c) on the ILS. Firstly,
you must establish on the ILS centreline (called the localiser). To do
this the a/c must have a heading of plus or minus 40 degrees from the
runway heading (ie on westerlies runway ILS closing headings lie
between 230 degrees and 310 degrees. On easterlies ILS closing
headings lie between 050-130 degrees. If the a/c actual heading is
not within these limits the a/c will not establish. To get an a/c to
establish you must append the letter 'E' to the end of the heading
instruction eg "A Right 240E". When the a/c is established on the
localiser the letters 'loc' appear in the appropriate place in the stack
display, and the a/c will turn to fly down the centreline.

The second stage of the approach is to establish the a/c on a sloping
radio beam (called the glide slope) down which an a/c may fly to get to
the runway. To establish on this beam you must be established on the
localiser and at the same altitude as the beam at the point that you
establish (as a guide the glide slope uses 300 feet for every mile from
touch down - thus at 10 miles you must establish outside 6 miles or
further if the a/c is above 2000 feet).

The safest way to ensure that you establish an aircraft on the glide
slope is to reduce the altitude to a level below the glide slope and fly
along until the glide slope coincides with the a/c altitude. When
established on the localiser and the glide slope the letters EST will
appear on the stack display.

If the a/c established on the localiser but not on the glide slope, you
may break off the approach once you have decided that it is too high
by simply inputting a heading instruction. If you do not break off the
approach the a/c will overshoot at about 1 mile from touchdown, this
means the a/c will turn back to be repositioned (and climb to 3000
feet if the a/c is below that).

On westerlies an a/c which overshoots, makes a right turn onto a
heading of 080 degrees and on easterlies a left turn onto a heading of
280 degrees. During the overshoot you do not have control of the a/c
until it is steady on the heading. You will be informed at the bottom of
the TV screen that " - Overshoot (too high)" (remember to
acknowledge using the space bar) and the letters "O/S" will appear
on the stack display.

N.B.  When on the ILS all a/c like to reduce speed, and although you
can instruct an a/c to fly at a speed of more than 180 knots, it will not
obey you. As stated previously you are not allowed to control an a/c's
speed within 4 miles from touchdown, and you will find that all a/c
reduce their speed significantly inside this range.

6. MIXED TRAFFIC WITH AIRSPACE RESTRICTION - EXERCISE 2

In this level you have to deal with a mixture of aircraft types. This
affects you in several ways.

Firstly there is a speed differential between the various types and you
must adjust the speeds accordingly to help your vectoring. Secondly
the different types have different rates of descent. This affects the
distances required to descend to a suitable glide slope altitude. Lastly
a/c will not establish on the localiser at more than 200 knots, thus you
must reduce a/c speed to ensure that their speeds are 200 knots or
less at the time of crossing the centre line (like all other variables
speed changes are not instantaneous and you must allow good time
for them).

The other concept introduced in this level is that of airspace
restrictions. As the Heathrow radar controller you are only entitled to
use certain areas. You must keep your a/c on the radar at all times.
Failure to do this will result in the message "-OUT OF RADAR
COVER".

Also you may only descend the aircraft below 7000 feet when they are
within an area called the Radar Manoeuvring Area (RMA). This is an area
which changes depending on the landing runway - on westerlies it is
a box whose top edge is a line East/West through LAM, bottom edge
is a line E/W through BIG, left hand edge is North/South through the
centre of Heathrow and right hand edge is N/S BIG-LAN. On 
Easterlies the box has the top edge E/W through BNN, bottom edge
East/West through OCK, left hand edge is the left edge of the radar,
right hand edge is North South through Heathrow. Descent below
7000 feet outside the appropriate RMA will result in the message
"Outside airspace".

Finally, the minimum safe level is 2000 feet (to ensure at least 1000
feet above the highest obstacle in this area). However you can only 
descend below 3000 feet inside a line 12 miles east or west of
Heathrow. Descend below 3000 feet outside 12 miles will result in the
message "LOW BELOW AIRSPACE".

Any airspace infringement will result in the loss of safety percentage
points in accordance with how long the relevant aircraft was outside
the allowed airspace.

7. LANDING INTERVAL AND SEPARATION - EXERCISE 3

Up to this stage the only criteria for landing safely has been safe
establishment on the localiser and glide slope. However to ensure
that each a/c remains safe, only one a/c is normally allowed on the
runway at a time. Hence the minimum time allowed between landing
a/c is 1 mins. This equates to about 4 miles distance between a/c on
the ILS but will vary with wind speed and direction.

To achieve the optimum landing interval experiment with different
distances between successive landing a/c and refer to the events
page to see the result in the landing times. If the interval between
landing a/c is less than 1 minutes the a/c will overshoot (as per
Exercise 2) with the message "-Overshoot (spacing)" meaning the
spacing on final approach is insufficient.

The other concept introduced here is perhaps the most fundamental
and important part of air traffic control, that of the method of keeping
a/c safely apart. At Heathrow, there are two basic types of separation
- vertical and radar. An a/c is vertically separated when it is at least
1000 feet above or below all other a/c in its vicinity. An a/c is radar
separated when it is 3 miles or more from any other a/c.

You must ensure at alt times that all a/c under your control are either
vertically separated or radar separated. If two a/c under your control
are less than 1000 feet vertically separated and less than 3 miles
horizontally apart you will get the message "-Not separated with-". If
the distance apart gets down to 1 mile or less you will get the
message "-Collision risk with-".

For each infringement of the separation rules you will lose safety
marks for as long as the infringement exists. If two a/c collide you will
fail the exercise!

8. VORTEX SPACING, OUTBOUND AIRCRAFT - EXERCISE 4

In this exercise you will see outbound and other traffic not under your
control. You can identity this traffic by the SSR label displaying the a/c
altitude only. You will see that some of the routes that the outbounds
take, cut into or go very close to, the RMA. It is still your responsibility
to ensure that your a/c remain separated from the other traffic. Failure
to do so will result in the message "-Not separated with?".

When an a/c flies through the air, it creates a disturbance in the air
similar to the wake of a boat in water. This is referred to as a Vortex
wake. A Vortex wake affects a following a/c in proportion to the 
difference in size between the two a/c. It presents a hazard to the
following a/c, especially at the latter stages of its approach and
landing.

To mitigate this hazard minimum interval times and distances must be
maintained as shown in the table below. As with landing intervals the
interval times can be equated with a radar separation and these are
shown in brackets.

LEADING
AIRCRAFT FOLLOWING AIRCRAFT
-------------------------------------------------------------------
      h           m           c            l

 h    2  min (5)  2 min (6)  3  min (7)  4 min (9)
 m    1 min (4)  1 min (4)  2  min (5)   3 min (7)
 s    1 min (4)  1 min (4)  1 min (4)   2 min (4)
 l    1 min (4)  1 min (4)  1 min (4)   2 min (4)

Remember that depending on the order in which you select a/c it is
possible to radically change the average landing interval.

Failure to give enough spacing will result in a Overshoot as in
exercise 2 and 3 and the message "-overshoot (Vortex)".

9. EMERGENCY TRAFFIC - EXERCISE 6

In this exercise one of your a/c will declare an emergency. You must
land the a/c as soon as is possible. You are marked on the speed with
which you land the a/c.

10. ADDITIONAL PROBLEM - EXERCISE 7

In this exercise not only do you have to contend with all the features of
exercise 6, but also some other event will happen which may delay
your traffic.

The possible events are:

1) An unknown a/c will fly through your airspace. You must apply the
normal rules of separation or you will lose safety marks.

2) One of your aircraft may lose contact with you (radiofail). You will
only know that a radio failure has occurred if you try to send an
instruction and get the response "radiofail". The a/c will return into
communication with you before very long.

3) Heathrow may lose a runway and you may have to go into Single
Runway Operations. This means that the runway is being used for
takeoffs as well as landings and therefore the minimum landing
interval will increase to 3 minutes (to allow one a/c to take off in
between a/c which are landing).

4) Your SSR may fail, leaving you with the a/c blips only. All other
equipment remains serviceable.

11. SUMMARY SHEET

ATC               Aircraft Traffic Control
ILS               Instrument Landing System
BNN               Bovington Holding Stack
LAM               Lambourne Holding Stack
OCK               Ockham Holding Stack
BIG               Biggin Holding Stack
SSR               Secondary Surveillance Radar
A                 Aircraft Identify and Altitude

RADIO COMMUNICATION
A - Altitude, S - Speed, L - Left, R - Right

AIRCRAFT TYPES       and           SPEED RANGES (knots)
h - heavy jet (Boeing 747)         160-250
m - medium jet (Trident)           160-250
s - small prop (Herald)            140-180
1 - light aircraft (Navajo)        120-180

AIRCRAFT HEADING AND DIRECTION INFORMATION
H - Holding in stack
O/S - Overshooting
loc - Localiser established
EST - Fully established

SPECIAL FUNCTION KEYS
"Space":- Acknowledges incoming messages
"Enter":- Evaluates instruction
"z":- Deletes line of instruction
"v":- Freezes exercise
"w":- Resumes exercise at normal rate
"y":- Speeds up exercise
"m":- Holds exercise and displays a page of events
"x":- Holds exercise and displays a page of information on
performance.
"Quote":- Returns information on aircraft altitude (A), heading (H) and
speed (S).

--------------------------------------------------------------------------------------
Re-edited Anthony Leader 's work with correct instructions by Frode Tenneb, 20051226.
