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 6½ miles ahead of 'F' and as 'A' is a heavy aircraft and 'F' is a medium aircraft type, 2½ 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 6½ 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 1½ 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 1½ 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) 2½ min (6) 3 min (7½) 4 min (9) m 1½ min (4) 1½ min (4) 2 min (5) 3 min (7) s 1½ min (4) 1½ min (4) 1½ min (4) 2 min (4) l 1½ min (4) 1½ min (4) 1½ 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 Tennebų, 20051226.