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Business School
Technological Education Institute of Larissa
Department of Project Management
School of Business Administration
Master in Business Administration
Module Title: Operations Management
Final Exam – Part B
INDICATIVE SOLUTIONS
Module Leader: Vassilis C. Gerogiannis, PhD
Module Tutors: Vassilis C. Gerogiannis, PhD and Vasiliki Kazantzi, PhD
March 2012
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Academic and Professional Conduct Exam Policy:
Using unauthorized notes, copying another
student’s work, or providing another student with
answers during an examination is a violation of the
exam policy.
Exam Instructions: You may bring notes into the
examination room not exceeding one side of A4
paper or 600 words. This is not an 'open book'
examination. The time duration of Part B
examination is 60 minutes. Please write your
answers clearly in designated areas. You are
allowed to use calculators and three pages of
blank paper. PDA, laptops, and other types of
computers are not allowed.
Part B of the final exam is the Analysis Part, comprising of 'seen stimulus material'
(case study) and 'unseen questions' which require in - depth analysis. You are
required to answer two questions from a choice of four. The maximum grade for Part
B is 50% points.
CASE STUDY
(taken from Slack et al. “Operations Management”, 4th edition, Prentice Hall, 2004)
Air traffic control: a world-class juggling act
Air traffic controllers have one of the most stressful jobs in the world. They are
responsible for the lives of thousands of passengers who fly every day in and out of
the world’s airports. Over the last 15 years, the number of planes in the sky has
doubled, leading to congestion at many airports and putting air traffic controllers
under increasing pressure. The controllers battle to maintain “separation standards”
that set the distance between planes as they land and take off. Sheer volume pushes
the air traffic controllers’ skills to the limit. Jim Courtney, an air traffic controller at
LaGuardia Airport in New York, says: “There are half a dozen moments of sheer
terror in each year when you wish you did something else for a living”.
New York – the world’s busiest airspace
The busiest airspace in the world is above New York. Around 7500 planes arrive and
depart each day at New York’s three airports, John F. Kennedy, LaGuardia and
Newark. The three airports form a triangle around New York and are just 15 miles
from each other. This requires careful coordination of traffic patterns, approach and
take-off routes, using predetermined corridors in the sky to keep the planes away
from each other. If the wind changes, all three airports work together to change the
flight paths. Sophisticated technology fitted to most of the bigger planes creates a
safety zone around the aircraft so that when two aircraft get near to each other their
computers negotiate which is going to take action to avoid the other and then alert
the pilot who changes course. Smaller aircraft, without radar, rely upon vision and the
notion of “little plane, big sky”.
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During its passage into or out of an airport, each plane will pass through the hands of
about eight different controllers. The airspace is divided into sectors controlled by
different teams of air traffic controllers. Tower controllers at each airport control
planes landing and taking off together with ground controllers who manage the
movement of the planes on the ground around the airport. The TRACON (Terminal
Radar Approach Control) controllers oversee the surrounding airspace. Each New
York air traffic controller handles about 100 landings and take offs per hour, about
one every 45 seconds.
TRACON controllers
The 60 TRACON controllers manage different sectors of airspace, with planes being
handed over from one controller to the next. Each controller handles about 15 planes
at a time, yet they never see them. All they see is a blip on a two-dimensional radar
screen, which shows their aircraft type, altitude, speed and destination. The aircraft,
however, are in three-dimensional airspace, flying at different altitudes and in various
directions. The job of the approach controllers is to funnel planes from different
directions into an orderly queue before handing each one over to the tower
controllers for landing.
Tower controllers
The tower controllers are responsible for coordinating landing and taking off. Newark
is New York’s busiest airport. During the early morning rush periods, there can be 40
planes an hour coming into land, with about 60 wanting to take off. As a result there
can be queues of up to 25 planes waiting to depart.
At LaGuardia, there are two runways that cross each other, one used for take off and
the other for landing. At peak times, air traffic controllers have to “shoot the gap” – to
get planes to take off in between the stream of landing aircraft, sometimes less than
60 seconds apart. Allowing planes to start their take off as other planes are landing,
using “anticipated separation”, keeps traffic moving and helps deal with increasing
volumes of traffic. At peak times, controllers have to shoot the gap 80 times an hour.
Most airports handle a mixture of large and small planes, and tower controllers need
to be able to calculate safe take off intervals in an instant. They have to take into
account aircraft type and capabilities in order to ensure that appropriate separations
can be kept. The faster planes need to be given more space in front of them than the
slower planes. Wake turbulence – mini-hurricanes which trail downstream of a
plane’s wing tips – is another major factor in determining how closely planes can
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follow each other. The larger the plane and the slower the plane, the greater the
turbulence.
Besides the usual “large” planes, controllers have to manage the small aircraft,
business helicopters, traffic spotter planes and the many sightseeing planes flying
over Manhattan, or up the Hudson towards the Statue of Liberty. The tower
controllers have to control the movement of over 2000 helicopters and light aircraft
that fly through New York’s airspace every day, being sure to keep them out of the
airspace around each airport used by the arriving and departing aircraft.
Ground controllers
As an aircraft lands, if it is handed over to the ground controllers who are responsible
for navigating it through the maze of interconnecting taxiways found at most
international airports. Some airport layouts mean that planes, having landed, have to
cross over the runway where other planes are taking off in order to get to the
terminal. All this needs careful coordination by the ground controllers.
Some pilots may be unfamiliar with airport layouts and need careful coaxing. Worse
still is poor visibility, fog or low cloud. At Kennedy airport, the ground radar does not
show aircraft type, so the controllers have to rely upon memory and constant
checking of aircraft position by radio to ensure they know where each aircraft is at
any time.
Stress
Dealing continually with so many aircraft movements means that controllers have
only a split second to analyse and react to every situation, yet they need to be right
100 per cent of the time. Any small error or lapse in concentration can have
catastrophic consequences. They can’t afford to lose track of a single aircraft,
because it may stray into someone else’s air space and into the path of another
aircraft. If the computer projects that two planes are about to fly closer than three
miles, the Conflict Alert buzzer sounds and the controllers have just seconds to make
the right decision and then transmit it to the pilots. Sometimes problems arise in the
planes themselves, such as an aircraft running short of fuel. Emergency landing
procedures cover such eventualities. At Kennedy airport, they have about one such
incident each day. As one controller remarked: “it’s like an enhanced video game,
except you only have one life”.
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QUESTIONS (Q1 – Q4)
Q1. Discuss and critically evaluate the planning activities involved in the case of air
traffic control.
Hint: Think about the specific types of planning activities that air traffic controllers
(ground, TRACON and tower) need to undertake in order to regulate air traffic in any
regular sequential and special situations.
Indicative answer to Q1:
There are three elements to the planning tasks described in this case. The first
concerns the drawing of the ‘invisible corridors’ in the sky through which the planes
are channelled. Related to this is the planning of how these invisible corridors are
changed to cope with different weather conditions. In effect, this is route planning, a
task which is undertaken in any transportation operation.
The second part of the planning activity involves setting out procedures for
emergency situations, such as emergency landings. This will involve predetermined
routines not only on what happens to the plane subject to the emergency, but also to
the other traffic in the air space and on the ground during the emergency.
The third part of planning will involve rough capacity planning. Airlines run to
schedules and therefore it is possible to forecast the expected number of planes
arriving in the air space at any particular time. In some ways this is similar to the
MRP (see Chapter 14 of the textbook) planning approach. So, if an aircraft is due at
a certain point in air space at a particular time it should be possible to forecast when
that aircraft will become the responsibility of the tower controllers, when it will
become the responsibility of the ground controllers and so on. Of course, this is in
theory only. Contingencies will have to be built into the plan to account for variation in
the actual arrival times of aircraft.
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Q2. Discuss the specific control activities undertaken by the air traffic controllers and
assess the impact of losing control on a particular aircraft to the other planes.
Hint: Take into consideration typical control procedures and how they work
Indicative answer to Q2:
Control in this case places particular emphasis on monitoring. In other words,
knowing where all the aircraft are at any point in time. Any loss of information means
loss of control. As with most control procedures, air traffic controllers will be
comparing what should be happening (where the aircraft should be) against what is
actually happening (where the aircraft actually is). The important issue here is that if
a particular aircraft is not approaching according to plan it will have an impact on all
the other aircraft in the air space at the time. The final part of control therefore means
adjusting the instructions given to the aircraft in order to take account of each other’s
position or deviation from position.
Q3. How would you critically evaluate the different problems that TRACON, tower
and ground controllers face?
Indicative answer to Q3:
TRACON controllers – There will be two types of problems for the control activity.
First, the aircraft must be kept apart while they are in a particular sector. This will
involve closely monitoring the position, direction and speed of each aircraft and
predicting their relative positions over time. In this the TRACON controllers are
assisted by the computers which help to predict whether aircraft are getting
dangerously close, or will become dangerously close. The second issue for TRACON
controllers will concern the handovers between different sectors. It is necessary for
one controller to have charge of all aircraft in his or her air space because it is the
position of the aircraft relative to each other which is important. However, the
consequence of doing this is that there must be a handover between sectors. This is
potentially a major failure point. Any failure to understand that responsibility has been
passed on, or loss of monitoring, could be disastrous here.
Tower controllers – The major problem for tower controllers is capacity. The major
bottleneck in capacity for air journeys is the airport itself. It is the tower controllers
who schedule and control the passage of planes into and out of the airport. This is
why the tower controllers at LeGuardia have to ‘shoot the gap’. Although this is
intrinsically risky, it increases the capacity of the airport substantially. Another issue
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for tower controllers is the variation between aircraft. The gap between planes takingoff or landing is a function of size because of the wake turbulence. This is the
equivalent to ‘changeover times’ in a factory. Just as changeover times for a machine
will depend on what is being changed from and what is being changed to, so the gap
between aircraft depends on the size of the two aircraft.
Ground controllers – Although ground control seems the least dangerous of the three
areas, several accidents have been caused at airports by aircraft straying onto the
runway. Ground control therefore is important from a safety point of view as well as
from an efficiency point of view. To be efficient, ground controllers must move aircraft
swiftly away from the runways so as not to cause bottlenecks or interfere with other
aircraft. Where the ground path cuts across runways, this is a particularly sensitive
task.
Q4. Discuss and assess the sequencing (scheduling) rules, which you think the tower
controllers use.
Hint: Take into account known sequencing rules and safety considerations
Indicative answer to Q4:
The most common sequencing rule in this case will probably be that of ‘due date’. i.e.
prioritising landing slots according to the aircraft schedules. However, this is probably
only a rough guide for aircraft controllers. ‘First in, first out’ (FIFO) rules, or orderly
queuing, is also likely to be a principle adopted by the controllers. However,
overriding all these will be a variant on the ‘customer priority’ rule which emphasises
safety. Any aircraft which is short of fuel or has an emergency on board will always
be given priority irrespective of its due date or its position in the queue.
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