internship report caa

Internship Report

Muhammad Owais Mehmood

NUST-PNEC

Internee Pakistan CAA

Electronics Engineering Depot

23rd Jun to 13th Jul 2012

Pakistan Civil Aviation Authority

Internship Report EED-CAA

List of contents

Introduction…………………………………………………………………………………………………3

Radar Central Workshop……………………………………………………………………………………4

Navigational Aids…………………………………………………………………………………………..9

HF (high frequency) section………………………………………………………………………………12

VHF/UHF section…………………………………………………………………………………………13

Telecom section…………………………………………………………………………………………...14

General electronics section………………………………………………………………………………..15


Pakistan's Civil Aviation Authority (CAA) is a regulatory authority, whose responsibility is to oversee

and regulate all aspects of civil aviation in Pakistan. Nearly all civilian airports and aviation facilities in

Pakistan are owned and operated by the CAA. CAA's head office is situated in terminal 1 of Jinnah

International Airport in Karachi.

Pakistan Civil Aviation Authority is a Public sector autonomous body working under the Federal

Government of Pakistan through the Ministry of Defense. It was established on 7th December, 1982 as an

autonomous body. Prior to its creation, a Civil Aviation Department in the Ministry of Defense used to

manage the civil aviation related activities.

CAA is also a member of the International Civil Aviation Organization (ICAO).

Electronics Engineering Depot (EED)

Electronics engineering depot (EED) in Karachi is the central and the biggest facility of CAA all over

Pakistan with respect to electronics engineering services provided by the authority. EED covers all the

electronic equipments which provide aviation services all over Pakistan. The EED holds following major

functions at CAA:

Procurement of all new aviation equipments (Radars, Voice logging systems, ILS etc) and

thorough testing of each equipment after purchase.

Providing on field repair and maintenance facilities all over Pakistan through its trained

personnel.

Workshops for extensive repair facilities at EED in case the equipment could not be repaired at

site.

The EED is divided into sub sections, each dealing with the equipment of its own concern. These sections

are:

Radar central workshop (RCWS)

Navigational Aids section

VHF/UHF section

HF section

General electronics section

Telecom section

Each section has the test equipment and trained personnel to deal with the problems occurring in their

respective fields.

Our training program at EED was designed in such a way so that that we could understand the

functionality of each section. We spent the allocated time in each section and got familiar with the

functioning of equipment as well as the repairing tools used. Following is the short detail of each

section‘s equipment and operation.

http://en.wikipedia.org/wiki/Jinnah_International_Airport




Radar Central Workshop (RCWS)

RADAR stands for ‗Radio detection and Ranging‘. Radar is an equipment which is used to detect objects

using ‗Radio Waves‘. It is a way to detect and study far off targets by transmitting a radio pulse in the

direction of the target and observing the reflection of the wave. It‘s basically radio echo.

In civil aviation radars are used to monitor and control commercial air traffic. A radar can provide

following information about a target which helps in managing the air traffic.

Target range

Target angles (azimuth & elevation)

Target size (radar cross section)

Target speed (Doppler)

Target features (imaging)

As far as civil aviation is concerned, the radars used can be divided into two main types:

Primary surveillance Radar

Secondary surveillance Radar

Primary surveillance Radar (PSR):

Primary Radar works on the principle in which the radar transmitter sends out a pulse of radio energy, of

which a very small proportion is reflected from the surface or structure of the target aircraft back to the

radar receiver.

The azimuth orientation of the radar antenna provides the bearing of the aircraft from the ground station,

and the time taken for the pulse to reach the target and return provides a measure of the distance of the

target from the ground station. The bearing and distance of the target can then be converted into a ground

position for display to the Air Traffic Controller. Target elevation (altitude) is not normally measured by

ATC primary radars. The advantage of Primary Surveillance Radar (PSR) is that it operates totally

independently of the target aircraft - that is, no action from the aircraft is required for it to provide a radar

return.

The disadvantages of PSR are that, firstly, enormous amounts of power must be radiated to ensure returns

from the target. This is especially true if long range is desired. Secondly, because of the small amount of


energy returned at the receiver, returns may be easily disrupted due to such factors as changes of target

attitude or signal attenuation due to heavy rain. This may cause the displayed target to 'fade'.

PSR‘s are further divided into two categories based on the type of signal emitted by the radar:

Continuous wave Radar

Pulsed wave Radar

In a pulsed wave radar system the pulse modulated signal are used for transmission. Duplexer is used

to use common antenna for transmission & reception. It can indicate the range of target. It requires

comparatively higher transmitting power. The circuits used in this system are comparatively complicated.

The performance is not affected by presence of number of targets. It is some times used for the mapping

of the airport area.

On the other hand CW radar uses modulated or unmodulated continuous signals for transmission.

Circulator is used or separate antennas are used for transmission & reception. Simple CW RADAR can

not indicate the range. The Doppler frequency shift of echo signal is useful for indication device. It uses

lower transmitting power. The circuits are simpler. The performance is unaffected by stationary targets.

The system gets confused by presence of large number of targets.


Specifications of the PSR used at JIAP

PSR Model: TA-10K

(Terminal Approach 10 cm Waveguide Klystron (Final Output Stage Power Amplifier))

(Frequency Band 2700 MHz to 2900 MHz)

Range (In Diversity Mode) = 98 NM at height of 30,000 feet

(When Both Channels are operational)

Peak Power (Per Transmitting Pulse) = 1.5 M Watts (maximum)

Peak Power (Per Transmitting Pulse) = 1.25 M Watts (operational)

Average Power (output) = 4 Kilo- Watts

Pulse Repetition Frequency = 666 Hz (operational)

Pulse Repetition Time Interval = 1.5 milliseconds (operational)

Pulse Repetition Frequency (optional) = 333 Hz (optional)

Operating Frequency Range = From 2700 MHz to 2900 MHz

Pulse Width = 1.7 Microseconds

Antenna Rotation Speed (High) = 10 Rpm

Antenna Rotation Speed (Low) = 5 Rpm

Standing Wave Ratio < 02

Range Resolution = 60 Meters (400 Nanoseconds)

Azimuth Resolution = 1.4 Degrees

Minimum Target Area to detect = 2 Square Meters (Minimum Radar Cross-Sectional

Area)

Secondary surveillance Radar (SSR):

The disadvantages of PSR led to the employment of another aspect of wartime radar

development. This was the Identification Friend or Foe (IFF) system, which had been developed as a

means of positively identifying friendly aircraft from enemy. The system which became known in civil

use as Secondary Surveillance Radar (SSR) relies on a piece of equipment aboard the aircraft known as a

'transponder'.

The transponder is a radio receiver and transmitter operating on the radar frequency. The target

aircraft's transponder responds to interrogation by the ground station by transmitting a coded reply signal.

The great advantages of SSR are three: firstly, because the reply signal is transmitted from the aircraft it is

much stronger when received at the ground station, thus giving the possibility of much greater range and

reducing the problems of signal attenuation; similarly, the transmitting power required of the ground

station for a given range is much reduced, thus providing considerable economy; and thirdly, because the

signals in each direction are electronically coded the possibility is offered to transmit additional

information between the two stations.

The disadvantage of SSR is that it requires a target aircraft to carry an operating transponder.

Thus SSR is a 'dependant' surveillance system. For this reason, PSR will operate in conjunction with SSR

in certain areas for the foreseeable future so that 'non-cooperating' targets, such as some light aircraft, can

be detected.


Modes of SSR

SSR has several modes of operation.

The basic civil mode is Mode A. In this mode the aircraft's transponder provides positive aircraft

identification by transmitting a four-digit code to the ground station. The code system is octal;

that is, each of the code digits may be any of the numbers 0-7. There are thus 4096 possible four-

digit codes.

Another principal SSR mode currently used is Mode C. In this mode the aircraft's altitude,

derived from on-board instruments, is transmitted to the ground station in addition to the identity.

A further mode, Mode S (or 'Mode Select'), is also used. Aircraft equipped with transponders

supporting this mode are assigned a permanent identification which can be selectively addressed

by the ground radar. This reduces problems of garbling between SSR returns from aircraft in

close proximity. Mode S also offers a wider range of data to be transmitted, including potentially

an uplink of data from the ground station to the aircraft although this capability is presently not

used in Pakistan.

Additional SSR Modes are used by military aircraft.

Specifications of secondary surveillance radar used at JIAP

SSR Model: RSM-870 (Radar Secondary Mono Pulse)

Range (One Way) = 200 NM (1 NM = 1852 Meters)

Interrogation Frequency = 1030 MHz

Reply from Transponder = 1090 MHz (This is not part of SSR Equipment)

Power Consumption = 600 Watts

Pulse Width = 0.8 Microseconds

Capacity = 300 Aircrafts (Processing)

Operating band = L – Band

Transmitter output Power (High) = 1.5 K Watts

SSR Modes (Available) = Alpha (Identity) & Charlie (Altitude)

For repair and maintenance of these radars and other radars installed all over Pakistan following

equipments are present in the RCWS:

1. AFIT-1500 In Circuit digital IC Tester (Excluding RAM & EPROM ICs) up to 24 Pins Digital /

TTL ICs only.

2. Tracker ―Huntron=5100DS‖ (Hardware change Cold Tester)

3. Micro-System Trouble Shooter.

4. Frequency Counter

5. Power Meter.

6. Synthesizer / Level Generator.

7. VHF Switch.


8. Relay Actuator

9. System Power Supply of Hewlett Packard.

10. Combinational System S-645 Programmable Fault Finder of Schlumberger. (Unserviceable)

11. Curve Tracer. Tektronix-571

12. EPROM Programmer ―Unisite‖

13. TEST BENCH OF RICS TXM-4200 SYSTEM

14. Chip Master Compact (Digital IC Tester)

15. Linear Master Compact (Analogue ICs Tester)

16. Component Analyzer (Up to 3-Pins Components Tester)

17. Relative Humidity & Temperature Tester.

18. ROBIN Microwave Leakage Tester.

19. BK Precision Auto Ranging Capacitance Meter, Model 830A

20. BK Precision Inductance Meter, Model # 875B

21. Fluke Scope Meter, Model # 199C

22. Fluke Multimeters, Model # 187

23. Toolkit Xcelite TC-100ST

24. Soldering Station ―Weller‖

25. Huntron Pro-Track-I Model 20

26. DATAMAN Universal EPROM Programmer

27. De-Soldering Station ―Weller‖ .

28. Huntron Scanner-I (part of Tracker)

29. Agilent Digital Colour LCD Oscilloscope

30. 6-GHz Spectrum Analyzer Model FSL6

31. Battery Load Tester (200A)

32. ERSA Infra-Red Rework Station IR/PL-550A

A secondary surveillance radar antenna mounted on primary radar antenna.

Visit to JIAP Area Control Centre:

During the internship period we visited the Area control centre which hosts the primary and secondary

radars as well as the air traffic management structure. People who mange air traffic through radar data are

called Air Traffic Controllers or ATCs. Radars are installed in different parts of Pakistan and the data

from other radars is sent to the Area control centre through a satellite link. This data contains video as

well as audio. There are different desks in Area control centre each of which manages traffic in the

assigned area.


Navigational Aids Section

The department of Navigational aids deals with equipment used in en route navigation and terminal

navigation.

En Route Navigation equipment: When the plane is successfully in the air after take off then the navigational aids used to guide the aircraft

to its destination are known as En route navigation. The most basic equipment used for en route

navigation are:

NDB (Non directional beacon)

VOR (Very high frequency Omni-directional Ranging)

DME (distance measuring equipment)

NDB:

Non-Directional Beacons (NDBs) are today the most common type of radio beacon found because of

their simplicity and relative cheapness. NDBs are basically a simple radio transmitter which radiates a

signal equally in every direction (hence 'non-directional'). This signal is modulated with a Morse code

identity signal.

This allows suitably equipped aircraft to 'home' on the beacon, bringing the

aircraft to a position overhead. From there, the aircraft can either track to

another beacon, or perform an instrument approach procedure using the NDB for

lateral guidance.

In Pakistan NDB operates at 190 – 525 Khz.

Models of NDBs. used by CAA are:

Aerocom 5401, 5034

Nautel ND-500, ND-2000

Southern Avionics SS - 1000

VOR:

VOR, short for VHF Omni directional radio range, is a type of radio navigation system for aircraft. A

VOR ground station broadcasts a VHF radio composite signal including the station's identifier, voice (if

equipped), and navigation signal. The identifier is Morse code. The voice signal is usually station name,

in-flight recorded advisories, or live flight service broadcasts. The navigation signal allows the airborne

receiving equipment to determine a magnetic bearing from the station to the aircraft (direction from the

VOR station in relation to the Earth's magnetic North at the time of installation). VOR stations in areas of

magnetic compass unreliability are oriented with respect to True North. This line of position is called the

"radial" from the VOR. The intersection of two radials from different VOR stations on a chart provides

the position of the aircraft.

D-VOR are for hilly area

C-VOR are for plane area

Comparison between D- VOR & C-VOR:

Doppler VOR beacons are inherently more accurate than Conventional VORs because they are more

immune to reflections from hills and buildings. The variable signal, in a DVOR, is the 30Hz FM signal.

In a CVOR it is the 30Hz AM signal. If the AM signal from a CVOR beacon, bounces off a building or

hill, the aircraft will see a phase that appears to be at the phase centre of the main signal and the reflected

signal, and this phase centre will move as the beam rotates. In a DVOR beacon, the variable signal will, if

reflected, seem to be two FM signals of unequal strengths and different phases. Twice per 30Hz cycle, the

instantaneous deviation of the two signals will be the same, and the phase locked loop will get (briefly)

confused. As the two instantaneous deviations drift apart again, the phase locked loop will follow the

http://en.wikipedia.org/wiki/File:JW_NDB_transmitter_329.0kHz.jpg


signal with the greatest strength, which should be that due to the line-of-sight signal. This will depend on

the bandwidth of the output of the phase comparator in the aircraft. Hence some reflections can cause

minor problems, but these are usually about an order of magnitude less than in a CVOR beacon.

Models of VOR used by CAA are:

C-VOR: Wilcox 585B

D-VOR: Thomson-CSF 512-C, 512-D

DME:

Distance measuring equipment (DME) is a transponder-based radio navigation technology that measures

distance by timing the propagation delay of VHF or UHF radio signals. Aircraft use DME to determine

their distance from a land-based transponder by sending and receiving pulse pairs - two pulses of fixed

duration and separation. The ground stations are typically co-located with VORs. A typical DME ground

transponder system for en-route or terminal navigation will have a 1 kW peak pulse output on the

assigned UHF channel.

In Pakistan DME operates at 962 – 1213 Mhz

Models of VORs used by CAA are: Wilcox 596B

Thomson-CSF 712

Terminal Navigation: The navigation techniques used to help the aircraft in landing is known as terminal navigation. The whole

set of equipment used in the process is known as Instrument Landing System (ILS).

Components of ILS

An instrument landing system (ILS) is a ground-based instrument approach system that provides

precision guidance to an aircraft approaching and landing on a runway, using a combination of radio

signals. These informations are:

Guidance information: the localizer and glide slope.


Range information: the outer marker (CM) and the middle marker (MM) beacons.

Visual information (high-intensity lighting arrays to enable a safe landing) PAPI approach lights,

touchdown and centerline lights, runway lights

Localizer:

The localizer signal provides information to guide the aircraft to the centerline of the runway

The localizer antenna is located at the far end of the runway.

The approach course of the localizer is called the front course.

The course line in the opposite direction to the front course is called the back course.

The localizer signal normally usable 18 NM from the field.

The Morse code Identification of the localizer consists of a three-letter.

Principle of Operation of Localizer: A localizer antenna array is normally located beyond the departure

end of the runway and generally consists of several pairs of directional antennas. Two signals are

transmitted on one out of 40 ILS channels between the carrier frequency range 108.10 MHz and

111.95 MHz (with the 100 kHz digit always odd). One is modulated at 90 Hz, the other at 150 Hz and

these are transmitted from separate but co-located antennas. Each the left of the runway centerline, the

other to the right antenna transmits a narrow beam, one slightly to the left of the runway centerline, the

other to the right.

Glide Slope: A glide slope (GS) or glide path (GP) antenna array is sited to one side of the runway

touchdown zone. The GP signal is transmitted on a carrier frequency between 329.15 and 335 MHz using

a technique similar to that of the localizer. The centerline of the glide slope signal is arranged to define a

glide slope of approximately 3° above horizontal (ground level). The beam is 1.4° deep; 0.7° below the

glide slope centerline and 0.7° above the glide slope centerline.

http://en.wikipedia.org/wiki/File:Whiteman_localizer.jpg


TDME:

Terminal Distance Measuring Equipment (TDME) gives the information of distance from touch down

point. Terminal DME, referred to as a TDME in navigational charts, is a DME that is designed to provide

a 0 reading at the threshold point of the runway, regardless of the physical location of the equipment. It is

typically associated with Glide Slope.

Marker Beacons:

Marker beacons are used to alert the pilot by audio and visual cues. It gives the distance from threshold

point on the extended center line of the runway, at a particular height. ILS contains three marker beacons:

inner, middle and outer. The inner marker is used only for Category II operations. The marker beacons are

located at specified intervals on the extended center line. All marker beacons operate on a frequency of 75

MHz.

Visit to Navigational Aids section and ATC control Tower:

During the internship we visited the navigational aids section at CAA headquarters and saw the

equipment currently being used for terminal and en route navigation. We went to the Equipment control

room which holds the communication equipment. We also got familiar with the Aeronautical message

handling system.

ATS Message Handling System (AMHS) also known as Aeronautical Message Handling System is a

standard for aeronautical ground-ground communications (e.g. for the transmission of NOTAM, Flight

Plans or Meteorological Data).

HF section

High frequency (HF) radio provides aircraft with an effective means of communication over long distance

oceanic and trans-polar routes. In addition, global data communication has recently been made possible

using strategically located HF data link (HFDL) ground stations. An aircraft HF radio system operates on

spot frequencies within the HF spectrum.

In the HF range (3 MHz to 30 MHz) radio waves propagate over long distances due to reflection from the

ionized layers in the upper atmosphere. Due to variations in height and intensities of the ionized regions,

different frequencies must be used at different times of day and night and for different paths. There is also

some seasonal variation (particularly between winter and summer). Propagation may also be disturbed

and enhanced during periods of intense solar activity. The upshot of this is that HF propagation has

considerable vagaries and is far less predictable than propagation at VHF.

HF section deals with the equipment of direct communication in Long Range, providing

maintenance repairing and upgrading of HF communication equipments, for four

purposes:

• Ground to Air Domestic

• Ground to Ground Domestic

• Ground to Air International

• Ground to Ground International


Presently HF RT is used as standby for ground to air communication, incase of Extended VHF failure. It

is also used for communication with the FIRs of Lahore, Kabul, Bombay and Delhi

HFRT(day) 10018 KHz 5658 KHz

HFRT(night) 3467 KHz 5658 KHz

HF SSB is used for ground to ground communication between CAA stations throughout the country.

VHF/UHF Section

This section deals with all the equipments of VHF/UHF used for the communication between Air

traffic Control to the plane or in other words ground to air communication. The maintenance of all the

VHF/UHF equipments from all over Pakistan comes under this department. There are various types of

antenna used in Communication of VHF/UHF, like whip antenna, long wire antenna, umbrella antenna,

half and full dipole antenna, VHF extended antenna etc.

Whereas, the general range of Frequencies used in CAA is from 118MHZ to 136 MHz.

Frequencies used by Civil Aviation Authority for different kind of Purposes are:

COMMUNICATORS MAIN(MHz) STANDBY (MHZ)

Tower controller 118.3 118.8

Ground controller 121.6 118.4

Surface frequency 121.8 123.0

Approach frequency 125.5 121.3

Radar frequency 123.3 127.3

VHF extended range 128.3 133.2

VHF emergency frequency 121.5 -

Since the range of VHF and UHF communication has line of sight restriction i.e. the receiver and

transmitter must be seeing each other for proper communication. This imposes a restriction over the usage

of VHF and UHF. However due to high quality communication in VHF and UHF band another technique

has been introduced which is known as extended VHF.

In extended VHF signals can be transmitted to far off places using satellite. The voice signal is

sent to the satellite through the up link and the satellite transmits it back to the destination station. Here

again the voice signal is transmitted in VHF band. Although this induces a delay in communication but

with modern equipment this delay is very small.


Latest VHF/UHF Equipments used by CAA are:

JOTRON TR-810 Multi purpose VHF/AM Transceiver

10W output power

Detachable front panel

Automatic muting facility

Output for voice-recording

Frequency range: 118-137 MHz

DC voltage range from 10 to 28V

25kHz/8.33kHz channel separation(selectable)

Front or rear connection for microphone input

A bright and clear graphical display for easy readout

Fast recall of 3 present channels via dedicated buttons

Built-in loudspeaker with possibilities for an external loudspeaker Rohde & Schwarz

R&S®Series4200(Software Defined VHF & UHF Radios)

VHF frequency range from 112 MHz to 156 MHz

UHF frequency range from 225 MHz to 400 MHz

Output power of 50 W for VHF and UHF

8.33/25 kHz channel spacing for VHF

8.33/12.5/25 kHz channel spacing for UHF

Serial interface for controlling automatic filters

Automatic main/standby operation

USB service port for configuration and software downloads

Remote control and remote monitoring via Ethernet interface

Best signal selection in the receiver

Suitable for data transmission in line with VDL mode 2 standard

In-band signaling for push-to-talk (PTT) and squelch (SQ) with the capability to set different tones

Telecom Section

Telecom section was originally developed to look after and maintain the intercom system within CAA but

now it is replaced by the modern PBX system.

PBX stands for private branch exchange. It is a network of telephones within an organization

and is also extended to the public telephone system or PSTN. Organizations that have more than a few

phones usually have an internal switching mechanism that connects the internal phones to each other and

to the outside world. A PBX is like a miniature Central Office switching system designed for a private

institution. A PBX usually has a console station that greets outside callers and connects them to internal

extensions.


A PBX is composed of three major elements.

1. Common equipment (a processor and a switching matrix)

2. CO trunks

3. Station lines

Besides this telecom section also takes care of the fax machines of CAA.

General Electronics Section

This section deals with all the rest of the equipment that comes into use of CAA. However the

major equipment comes from the following departments

DVLS (digital voice logging systems)

PA (public addressing) systems

FIDS (flight information display systems)

DVLS:

Formerly VLS was used for recording all types of conversations, works on the analog principle of

magnetic tape recording. The VLS tape can record a day‘s recording and has to be replaced the other day.

The system is being replaced by the DVLS. It is the most important and major equipment with which GE

deals. This is the Latest machine use for the recording all types of conversation. recording stuff is

reserved for 30 days in DVD-RAM . The model of DVLS

used by CAA is Marathon Evolution.

ASC MARATHON EVOLUTION

World‘s First Linux-based communications recorder

Multimedia recording from, Traditional telephony

and radio, VoIP (Voice over IP), Trunked radio

Fax data, Screen data

The system can be configured to record, live monitor and archive communications at one location

and to provide


Search and replay facilities locally or via LAN / WAN, Intranet or Internet.

Analog inputs: 4 ... 192 channels

Digital inputs: 4 ... 120 channels or mixed configuration of analog / digital / VoIP

VoIP: 4 ... 32 channels (active) 4 ... 120 channels (passive)

PA systems:

A public address system (PA system) is an electronic amplification system with a microphones,

preamplifiers and/or signal routers mixer, which allows variation in sound levels, amplifier to increase the

sound and loudspeakers placed in convenient locations around the broadcasting area, used to reinforce a

sound source. The user speaks into a microphone, and the sound is transmitted through connected cables

to the area surrounding the speakers.

FIDS:

Flight Information Display Systems (FIDS) help improve communications and keep passengers

constantly informed of travel information. To manage the heavy and ever increasing passenger traffic, an

airport in the Middle-East needed terminal-wide FIDS that broadcasted information from a constantly

updated database to numerous multimedia displays placed strategically throughout passenger facilities.

These indoor displays needed to supply timely information regarding flight arrivals/departures, gate

http://en.wikipedia.org/wiki/File:Public_Address_System_rack_1.jpg


assignments, waiting hall locations, baggage area assignments, and weather forecasts—as well as

entertainment and advertising content. Considering the airport handles millions of passengers per year, a

reliable mission-critical solution was needed. Any potential onsite technical problems could cause serious

consequences that might disrupt the operation of the airport.

System Characteristics

1) Diversification of contents and formats: multiple media formats, including images, texts, Flash, MPEG

video, etc.

2) Diversification of page display: pages for flight and public information are displayed alternately. The

latter is displayed in shorter time.

3) Strictly obey the rules of display according to the time order of flights.

4) Continuity of display: when the video public information and flight information are displayed on the

same page, the existing video display will not be interrupted due to the page refresh caused by

dynamic modification of flight information.

5) Public information display is to demonstrate the information related to airport operating issues

including lost notice, urgent notice, change of boarding gates and delay of flight.

internship report caa

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