Critical Point

The main purpose of commercial aviation is getting people from varied parts of the globe closer. Qantas airplane in October last year, a Boeing 787-9 covered roughly 10,000 miles during its journey from New York to Sydney. The aircraft was in the air for a non stop 19 hrs and 16 minutes.These figures are staggering and long haul flights look more and more promising with the innovations of these aircraft’s in the future post the pandemic.The most important point to take out of this for an aviation enthusiast is how safe is the airplane when it is flying for long hours continuously in the air?

There are a number of failures that can occur during long haul flights and with the help of alternate airfields on the route, a pilot can take a decision to divert and land at one of the alternates.The big question is what if there are no alternates on the route or on one of the long oceanic legs of the flight? The answer is to that is the Critical Point calculated by pilots before their flight.

What is Critical Point

Critical Point (CP) also know known as Point Of Equal Time (PET) is the decision point between two airfields from which it would take the same time to fly to either airfield.In other words, CP or ETP is a geographical point in the flight where the aircraft would have the same flying time to continue on to a given airport or to turn back to another suitable airfield.

The knowledge of CP enables the pilot to decide which way would it be quicker for him to proceed either to the destination or return to the place of departure if they face a time critical problem such as cabin fire or an flight medical emergency.

NOTE: Before you read any further, I would highly recommend having a quick look at the Wind Triangle post in case you haven’t WIND TRIANGLE. The study of Critical Point requires concepts from the wind triangle that would help us in calculating the calculating the Ground speed so please check that out.

Operative Points

1.Lets consider a route from point A to point B which is 200 NM long. Our aircraft has a TAS of 100 knots and there are no winds. In this scenario, the critical point or point of equal time is the point of equal distance, that is 100 NM. What this shows that at the 100 NM mark, the time to destination or time to return back to departure airfield would be same.

2.Lets take the same example as above and consider a headwind of 20 knots.With a 20 knots headwind, the ground speed outwards (GS out) from A to B will reduce by 20 knots and become 80 knots and if you consider the opposite, that is if you return to A and direction of travel is from B to A then your ground speed will increase from 100 to 120 knots and we will call this as ground speed home (GS home).Hence as the GS home is more than GS out, the CP moves forward than what it was in still air conditions.As we saw in this example, it is safe to say that in case of headwind component, distance to CP will always be more than mid way.

3.Lets take the same example as above and consider a tailwind of 20 knots.With a 20 knots tailwind, the ground speed outwards (GS out) from A to B will increase by 20 knots and become 120 knots and if you consider the opposite, that is if you return to A and direction of travel is from B to A then your ground speed will decrease from 100 to 80 knots and we will call this as ground speed home (GS home).Hence as the GS out is more than GS home, the CP moves backward than what it was in still air conditions.As we saw in this example, it is safe to say that in case of tailwind component, distance to CP will always be less than mid way.

From the above points 2 and 3, the effect of a headwind and tailwind makes the critical point move in the direction on the wind .

4.We have addressed the effect of wind on the Critical Point but how do we know the distance to the CP (DCP) from the point we are calculating it and the time to CP. Lets consider we are traveling a distance ‘D’ from A to B and we know our TAS and winds. With the help of our TAS and winds we can calculate Ground speed.If we want to calculate our CP from position A then the ground speed from A to CP can be termed as GS OUT (O) and the ground speed from CP to A can be termed as GS HOME (H).The distance and time to CP can be found out by simple formulas as shown in the picture.

5.To get used to the calculating the DCP and time to CP we shall consider an example. Total distance from A to B is 750 NM. The aircraft TAS is 250 knots with with a tailwind of 30 knots on departure. Calculate the distance and time to CP?

6.There might be instances where the winds are directly abeam (90 degrees) to your track. In such cases, the distance to CP will always be midway and whether we proceed outbound or inbound, both ways the aircraft will face headwind.

Lets consider an example, with our route distance being 270 NM. The track of our flight is 030 degrees and the wind is coming from 120 degrees (90 degrees to the track) at 35 knots. The true air speed is 125 knots. Find the distance to CP and time to CP?

Even when we have a look at the picture on the right, the calculations show us the same thing that the critical point is mid way of the total distance.

In this weeks post we covered a very important topic of flight planning that is used by pilots.I hope you liked reading the post and gained some insight from it. Please feel free to email me or post in the comments section, any aviation related topics you would like to gain knowledge on. Until next week, stay safe and stay healthy.



Vertical Speed Indicator

Instruments in an aircraft are priceless for pilots. They are specially trained under the hood to get used to the instruments without looking outside the aircraft and understanding how the aircraft responds while flying only on instruments.After a student pilot has got used to the attitudes that he needs to set while flying visually with the horizon, he gets introduced to basic instrument flying.

In order to safely fly any aircraft, a pilot must understand how to interpret and operate the flight instruments. The pilot also needs to be able to recognize associated errors and malfunctions of these instruments.When a pilot understands how each instrument works and recognizes when an instrument is malfunctioning, he or she can safely utilize the instruments to their fullest potential.

Pressure Instruments

Instruments in an airplane can be categorized in several different ways,those are, pressure, gyro, vacuum and radio instruments. After that there is the magnetic compass which works on a different principle. The vertical speed indicator works on the principle of rate of change of differential static pressure.

Static Pressure

By definition, static pressure is the pressure exerted by a column of air of the atmosphere on a unit area.It can also be called the ambient pressure and is always present if the aircraft is moving or is at rest.Static pressure is simply the barometric pressure of the local area. If you fly at any altitude, the atmospheric pressure at that altitude can be called static pressure.Static vents on either side of the fuselage help in the measurement of static pressure.

The reason for two static vents is for redundancy purposes as a static vent might get blocked and in cases of crosswind and side slip maneuvers.In the latter cases, there would be a difference in the measurement of static pressure from the vents and hence to avoid incorrect indications both the vents are connected to each other from the inside to average out the result.

Vertical Speed Indicator

The VSI, which is sometimes called a vertical velocity indicator (VVI), indicates whether the aircraft is climbing, descending, or in level flight. The rate of climb or descent is indicated in feet per minute (fpm). If proper, the VSI indicates zero in level flight.


The VSI display two types of information :

• Trend information shows an immediate indication of an increase or decrease in the aircraft’s rate of climb or descent.
• Rate information shows a stabilized rate of change in altitude.

The VSI indicator in the aircraft uses a logarithmic scale. The reason for using a logarithmic scale is that the lower values have more spacing and the higher values have less spacing. Therefore, it becomes easy to identify even a slight change in the VSI needle from zero position and can be easily recorded.


  • The VSI as we mentioned above works on principle of rate of change of differential static pressure.Before we get to understand how this difference in static pressure is achieved, it is helpful to know the components of a vertical speed indicator.
  • The vertical speed indicator is made up of:
    • CAPSULE:The capsule is connected directly to the static line to receive air of existing atmosphere on one side and through linkages to the VSI pointer from the other side.
    • CASING:The capsule is placed in an airtight casing. The casing also receives static pressure from the static line, however, there is a lag in which it gets its pressure.This helps to create the difference in static pressure which is required for the VSI operation.
    • METERING UNIT/ CHOKE:Metering unit is used to achieve the time delay of static pressure between what is fed to the capsule and the case.The metering unit has a lot of names such as choke, restricted orifice or calibrated leak but the use of it remains the same, that is, to prove the necessary lag to feed the area outside the capsule.
  • When the aircraft is on the ground or in level flight, the pressure inside the capsule and casing is the same and there is no difference in static pressure. This will result in the VSI needle indicating zero.
  • When the aircraft is climbing, the atmospheric (static pressure) reduces as we climb and this is fed to the capsule. The same pressure is fed to the casing through a metering unit that will cause a delay and hence the pressure in the capsule will be less than in the casing which will cause the capsule to compress and indicates a RATE OF CLIMB.
  • When the aircraft is descending, the atmospheric (static pressure) increases as we descend and this is fed to the capsule. The same pressure is fed to the casing through a metering unit that will cause a delay and hence the pressure in the capsule will be more than in the casing which will cause the capsule to expand and indicates a RATE OF DESCEND.


To understand what the VSI needle will indicate in case the static vent gets blocked, I would recommend viewing the diagram used in operations.

  • CASE 1: The aircraft flying level and the static vent is blocked. As flying level, VSI indicates zero and would continue to indicate zero even if the static vent is blocked.
  • CASE 2:During climb, static pressure vent is blocked. Due to the delay in the casing, the Rate of Climb indication will progressively reduce and settle to zero.


  • POSITION ERROR: The position error is on account of the incorrect location of the static vents.Due to this error, the VSI will wrongly indicate a climb or descent when speed is suddenly changed and is most noticeable during take off acceleration.
  • INSTRUMENT ERROR: It is on account of manufacturing imperfections.
  • LAG ERROR: The pointer would take sometime to indicate the change from the time it senses it. This error is most noticeable during prolonged climb or descents at a high rate.
  • MANOEUVRE INDUCED ERROR: Different changes in attitude and configurations of the aircraft will lead to this type of error.This leads to false indications of rate of climb or descent.
  • HYSTERISIS ERROR: When an aircraft is flying at a flight level for a considerable period of time, it will result in the VSI unwilling to respond to changes in static pressure values.

Instrument Check

As part of a preflight check, proper operation of the VSI must be established. Make sure the VSI indicates a near zero reading prior to leaving the ramp area and again just before takeoff. If the VSI indicates anything other than zero, that indication can be referenced as the zero mark. Normally, if the needle is not exactly zero, it is only slightly above or below the zero line. After takeoff, the VSI should trend upward to indicate a positive rate of climb and then, once a stabilized climb is established, a rate of climb can be referenced.

Instantaneous Vertical Speed Indicator (IVSI)

  • To overcome the problem of lag, the Instantaneous Vertical Speed Indicator (IVSI) implements the use of accelerometer (an electromechanical device used to measure acceleration).The IVSI uses a dashpot or a vane type accelerometer.
  • The main advantage of using such an accelerometer is that it responds very quickly to changes in altitude.
  • The sensitivity of a dash pot IVSI is very high and this results in the instrument over reacting in turbulent flying conditions and resulting in false indications and the errors are termed as turning errors. At the time of initiating a level turn, the IVSI momentarily indicates a climbing turn.
picture credit:dutchops

Fact of the Week

Qamdo Bangda Airport, also called Qamdo Bamda Airport, is a plateau airport located in Bangda Prairie, Hengduan Mountains.The Qamdo Bangda Airport started its construction on December 2, 1992. The Air Force only spent 83 days on fixing the 5,500m long and 45 m wide airport runway – the longest one in the world and the airport is 4,334m (14,219 ft) above sea level, which makes it the second highest airport in the world.

 Climate environment of the Qamdo Bangda Airport is quite hostile. Wind speeds up to 30m per second in winter. Besides, the temperature often drops to 20 degrees centigrade below zero in winter and spring, which is difficult for flight operation. Due to its high elevation, the airport oxygen level is only 50% of that of sea level.he airport did a reconstruction and expansion to repaire the runway, building a new terminal of 5,018 square meters. From June 22 to July 15, 2013, the airport was shut down for a further maintenance of the old runway. A second runway is under construction from 2015.

picture credit: Tibet Discovery

We are done for this weeks post. I hope you gained some new knowledge from the world of aviation.If you did, please don’t forget to like this post and share it with your fellow aviation enthusiasts. Until next week, stay safe and stay healthy.



Hypoxia in aviation is a problem of altitude.It is very important that pilots are alert on how the human body responds to flying at high altitudes when they transition from their light training airplanes to complex high performance aircraft’s that are capable of operating at high altitudes and high speeds.Before we get to know what hypoxia is, we need to understand the relationship of oxygen in our body with altitude.

Oxygen and Altitude

Oxygen is a colourless and odourless gas that makes up 21% of the earths atmosphere by volume. The brain weighs approximately 2% of our body weight but consumes almost 20% of the oxygen that our body needs for its normal functioning.Brain cells die if they don’t receive oxygen for 2 minutes.

Alveoli are tiny sacs in the lungs of a human body where the exchange of oxygen and carbon dioxide takes place through breathing in and out. Therefore it is clear that at anytime the concentration of oxygen should be high and that if carbon dioxide should be low in the alveoli.

According to International Standard Atmosphere (ISA) conditions, the standard pressure at mean sea level is 1013 hectopascal (760 mm Hg). As mentioned above if 21% of the atmosphere is filled with oxygen , it means out of the 760 mm, 160 mm is oxygen. This is what we call partial pressure of oxygen in the air. The human body takes its oxygen from alveoli in the lungs where the partial pressure of oxygen is relatively less (103 mm Hg) as compared to the partial pressure of oxygen in the atmosphere (160 mm Hg).

As we move up to higher altitudes, the amount of partial pressure of oxygen generated by the alveoli also starts reducing. Human beings living at higher altitudes like 10-12 thousand ft above mean sea level, their alveoli produces partial pressure of 55 mm Hg oxygen which is considered to be the minimum for normal operations.

Hence as we go above 10 000 ft, oxygen needs to be added to the cabins air supply .The oxygen that gets added is sufficient to maintain a partial pressure of oxygen that is similar to what humans require on ground (103 mm Hg). A stage is reached where 100% oxygen supply is required to maintain the 103 mm Hg of partial pressure ( what we breathe on the ground)

This stage is at approximately 33,700 feet. However this does not mean that we cannot go above 33, 700 feet, as we discussed above for our normal operations in the body we require a minimum of 55 mm Hg of partial pressure ( what we would breathe at 10 000 feet) . With 100% oxygen supply, this is reached at 40 000 ft .


Hypoxia ( HYPO= less , OXIA=oxygenation) is a condition where not enough oxygen makes it to the cells and tissues in the body. This can happen even though blood flow is normal. Hypoxia can lead to many serious, sometimes life-threatening complications.The most common causes of hypoxia in aviation are: flying, non-pressurized aircraft above 10,000 ft without supplemental oxygen, rapid decompression during flight, pressurization system malfunction, or oxygen system malfunction.

Types of Hypoxia and their Causes:

  • Hypoxic Hypoxia (H) :The reason for this type of hypoxia is the result of low levels of oxygen in the bloodstream. The main reason for this condition occurring in aviation is altitude. As we have discussed in detail above that with increase in altitude, there results a fall in atmospheric pressure and the consequent resultant drop in the partial pressure of oxygen leading to Hypoxic Hypoxia.
  • Anemic Hypoxia (A) :In this type of condition , the lungs are working perfectly but the red blood cells which are the carriers of oxygen in the blood decrease. The reason for the decrease in the count can be due to heavy bleeding, anemia, some type of cancer and lastly the intake of carbon monoxide.
  • Stagnant Hypoxia (S) :In stagnant hypoxia, there is enough oxygen available to breathe but the blood flow is compromised for some reason like a heart attack and the blood is not received by the cells of the body tissues to support their metabolism.Stagnant hypoxia also occurs when the body is exposed to cold temperatures because the blood flow is decreased to the extremities.
  • Histotoxic Hypoxia (H):In this category of hypoxia, there is enough oxygen to breathe and the oxygen is also being carried by the blood but the cells do not accept it. For pilots, some of the primary factors causing hystotoxic hypoxia are alcohol, narcotics and cyanide.

Signs and Symptoms of Hypoxia:

Hypoxia is easy to succumb to the human body and affect each body with varying intensities. even though the condition does not have an alarming warning system to protect us against us the treat, the signs and symptoms are easily recognizable if we identify them. As pilots we need to km=now that no matter the type or cause of hypoxia, the signs and symptoms for each type do not differ a lot and neither do they affect our flying skills in separate ways.

The signs and symptoms are mentioned below:

  • The onset of hypoxia can be accompanied by a feeling of well being, known as euphoria.
  • Impaired Judgement
  • Headache
  • Tingling in hands and feet
  • Hyperventilation
  • Memory and Muscular Impairment
  • Sensory Loss
  • Cyanosis (a bluing of the body extremities)
  • Tunnel Vision
  • Fornication ( a feeling of ants under the skin)
  • Hyperventilation (over breathing)
  • As hypoxia keeps intervening with reasoning, it gives rise to unusual fatigue and finally loss of consciousness or death.

Time of Useful Consciousness (TUC)

This is the period of time from interruption of the oxygen supply, or exposure to an oxygen-poor
environment, to the time when an individual is no longer capable of taking proper corrective and
protective action.It is also know as Effective Performance Time (EPT). We are clear by now that as altitude increases the risk of hypoxia increases and due to that our time for useful consciousness will decrease. Hence, altitude and time for useful consciousness are inversely proportional.The chart below will make it even more clear:

Immediate and Preventive Actions

  • One way to avoid the risk of hypoxia for a pilot to make sure that his aircraft is correctly pressurized above 10,000 feet.
  • In case the aircraft cannot be pressurized, carry supplemental oxygen (don your oxygen mask).
  • If both the above options are not available, it is safe to be flying below 10 ,00 feet and even if we fly above that altitude due weather or terrain, we limit our time to a maximum of 1 hour if flying between 10 to 14,000 feet and 30 minutes if flying between 12 to 14,000 feet.
  • The most important action will always be to use supplemental oxygen above 10,000 feet in day and 5,000 feet at night ( vision gets impaired at a lower altitude in the night due to hypoxia).
  • The most effective way to prevent hypoxia is through education and experience.When pilots are trained in the proper use and care of their pressurization systems and supplemental oxygen equipment, and are aware of their personal hypoxia signs and symptoms, they are safer and better prepared to meet the challenge of flying in an oxygen-poor environment.

Fact of the Week

Boeing’s Everett Site is heralded as having the largest manufacturing building in the world, producing the 747, 767, 777, and the 787 airplanes. Thousands of aerospace employees in Everett support aircraft fabrication and production, product development, aviation safety and security and airplane certifications. Other production areas at the site include the paint hangars, flight line and delivery center. Originally built in 1967 to manufacture the 747, the main assembly building has grown to enclose 472 million cubic feet of space over 98.3 acres.

In January 1967, the first production workers arrived at Everett, and on May 1, 1967, the major assembly buildings opened their doors for the first time. Thousands of people from all over the world visit the Everett site every year. VIP visitors have included U.S. presidents, international dignitaries, CEOs, astronauts and other celebrities.Click the link to know more about this huge airplane manufacturer building

We are done for this week. I hope you gained some new insight from this post and if you did please share with it with your fellow aviators and aviation lovers. I encourage you to like this post as it gives me great confidence from your’e interest in these topics. If you have any suggestions please feel free tom drop in a comment or an email, I would be happy to reply. Until next week , stay safe and stay healthy.



Aviation makes the world a smaller place and international airlines play a huge role in connecting people from across the globe with different cultures together.International airlines as many international companies all over the world hire people from different countries. For example, Emirates Airlines recruits pilots from all over the world and there are 52 different nationalities of pilots currently in the airline. The top three nationalities being British, Australian and Canadian.

Need for Aviation Language

With such diversity in the crew, the focus on communication is very important. The flight crew, cabin crew , air traffic controller , in short, the entire aviation community need to communicate in a common language. In the history of aviation , a lot of accidents and incidents such as the Tenerife Airport runway collision or the Charkhi-Dadri Mid Air collision have time and again reminded us as aviators the importance of communication.

A)Controller: Descend two four zero zero feet.
In this message, the similarity between “two” and “to” led the pilot to understand 400 feet instead of 2 400 feet. The aircraft crashed into high ground.

B)Pilot: We are at take-off.
In this message, the controller understood that the pilot was waiting in position to begin the take-off, whereas the aircraft had actually begun to accelerate along the runway. It collided in foggy conditions with another aircraft.

The points A and B highlight the ease with which miscommunication can be of serious consequence and impact safety.

What is Aviation Language?

The field covered by the term “aviation language” is relatively broad. It could include all of the language uses of many different professions (engineers, technicians, commercial staff, flight crews, etc.) within the aviation domain.The sole object of ICAO language proficiency requirements is aeronautical radiotelephony communications, a specialized subcategory of aviation language corresponding to a limited portion of the language uses of only two aviation professions — controllers and flight crews.

The language spoken in aviation is called ICAO (International Civil Aviation Organization) English. The ICAO, recommended English to be the language for aeronautical radiotelephony communications in 1951 as most of the English speaking countries dominated the aviation market.English is a first language or a widely used national language in approximately sixty counties and is an important second language in many more.Non-native users of English outnumbered native users at the start of the 21st century by approximately 3 to 1.

Language Proficiency Requirements

Since the 5th of March 2008, every pilot or flight crew member coming into contact with international aviation communication including air traffic controllers must pass a language proficiency exam in compliance with ICAO regulations.

A language proficiency rating scale was developed as a guide to judge pilots and air traffic controllers over their command on the language. The scale was only tests speaking and listening skills and does not address reading and writing skills.

The scale is divided into 6 levels. Levels 1 to 3 on the rating scale assist the examiner on recruiting and training the candidate while Levels 4 to 6 set up a minimum operational requirement. Hence pilots need to need to make sure their language skills meet at least the ICAO Level 4 requirements.If a pilot gets a level 6 rating, he is granted an exemption from the need to be re-evaluated from time to time.

The Language proficiency exam tests consists of pronunciation, structure (use of tense etc), vocabulary, fluency, comprehension and interaction. However to acquire an ICAO Level 4 rating does not require high degrees of grammatical correctness and traditional English language .

Level 1,2 and 3 on the Rating Scale
Level 4 ,5 and 6 on the Rating Scale

ICAO Phonetic Alphabet

The International Civil Aviation Organization created the international radiotelephony alphabet, tied to the , English Alphabets . They were created to avoid the confusion between similar sounding alphabets such as B and D or M and N. Therefore on the radio the ATC will instruct the pilots the to “ Hold short of holding point APLHA” and not “Hold short of holding point A” .


The foundation’s of standard phraseology were laid in the Annex 10 Volume 2 of the ICAO Annexure. Standard phrases are of extremely useful in emergencies and unusual situation and helps keep communication concise.Therefore learning the new aviation alphabets is not the only difference in the aviation language, pilots and ATCs need to have these standard words and phrases registered in their memory.

There are about 300 standard words and phrases that are used. Some of the most common ones are listed below along with their meaning:

  • Acknowledge: Let me know when you have received and understood the message
  • Affirm: Yes
  • Approved: Permission for proposed message granted
  • Break: I hereby indicate the separation between portions of the message (to be used where there is no clear distinction between the text and other portions of the message)
  • Break Break: I hereby indicate separation between messages transmitted to different aircraft in a very busy environment
  • Cancel: Annul the previously transmitted clearance
  • Check: Used to examine a procedure or system
  • Cleared:Authorised to proceed under specific conditions
  • Confirm:Have you correctly received the message ?
  • Contact : Establish radio communication with …
  • Correction: An error has been made in the previous transmitted message. The corrected message is …
  • Disregard: Consider the transmission as not sent
  • I say again: Repeating for clarity of the message
  • Maintain: Continue in accordance with the condition specified . for eg, ‘Maintain VFR’ (VFR- Visual Flight Rules)
  • Mayday: My aircraft and its occupants are threatened by grave and imminent danger and/or I require immediate assistance
  • Negative: Permission not granted
  • Over: My transmission has ended and I expect a response
  • Pan Pan: I have an urgent message to transmit concerning the safety of my aircraft, or other vehicle or of some person on board, or within sight, but I do not require immediate assistance
  • Read Back: Repeat all, or the specified part, of this message back to me exactly as received
  • Report: Pass me the following information
  • Request: I wish to obtain
  • Stand by : Wait , I will connect with you in a bit
  • Wilco: I have understood your message and will comply with it

FACT OF THE WEEK: Mason Andrews, age 18 Yrs 163 Days became the youngest person to circumnavigate the globe in an aircraft when he completed his journey in Monroe, Louisiana, USA on the 6th of October 2018. Mason flew a single engine Piper PA -32 around the world in 76 days.

Andrews’s journey was only made possible by initially telling his parents he was flying solo across the Atlantic and no further. His parents were resistant to even allow this trip, but they were eventually persuaded by the scale and detail of his preparations. It was only later that they learned of the worldwide trip he was planning.

This is it for this weeks post. I hope you gained some new knowledge from it. Please share it with your fellow aviators and enthusiasts if you liked this post. Feel free to comment for suggestions. Until next week , stay safe and stay healthy .



The development of electronic communications over a period of time has been a big advantage for the aviation industry.The Airbus believes in Fly , Navigate and Communicate . With the help of electronic communication, the emphasis on verbal communication between the pilots and the air traffic controller has reduced severely .This helps aviators to concentrate on flying the aircraft which is of utmost importance.

Transponders and squawk codes help in reducing verbal communication and help maintain a silent cockpit.They assist the air traffic controller in knowing the aircraft position on their radars.



A transponder (XPDR) as the name suggest is a transmitter and receiver. It is an electronic device that produces a response to an interrogation signal sent by the air traffic controller.

It was initially used in the military to identify aircraft’s . It was termed as ‘Identification of Friend or Foe’ as a military aircraft sent interrogation signals to another aircraft to find out if they are their friends or foes .

However , in commercial operations, as we only have friends we do not use these terms . The Air traffic controller assigns each aircraft a squawk code which enable them to identify the aircraft on their radar and other aircraft’s collision avoidance system.

Conventional Transponder


The ground based equipment transmits interrogation pulse signals on a frequency of 1030 MHz (Megahertz) and receives on 1090 MHz.While the Aircraft transponder , transmits on 1090 MHz and receives on 1030 MHz .

Signals from the ground transmitter are transmitted in pair of pulses that are coded and each code is known as a MODE.There are a few modes that will be discussed down below. The replies from the aircraft are however in all directions.

The ground receiver then decodes the reply from the aircraft and displays the necessary information such as aircraft call sign, altitude , speed etc on the radar.


The different modes of transponder help us gain different information of the aircraft .

  • MODE A:This type of transponder provides an identification code only .
  • MODE C: In Mode C, along with identification code , aircraft pressure altitude is provided as well .
  • MODE S: In Mode S (selective) ,there are a number of details that can be provided along with aircraft identification code and altitude. For example, aircraft ground speed , destination of the aircraft , desired track etc.

A Mode C transponder is commonly found in general aviation aircraft’s where as the commercial jets are equipped with Mode S transponder. In the flight plan that is needed to be file before a flight , it is necessary to mention the type of surveillance equipment (transponder) installed on board. In the ICAO flight plan, the necessary details are included in box 10,that is , Equipment ( more on flight plan in a separate post).



Once the ground receiver has decoded the information, the radar displays the necessary information depending upon the mode of transponder. The different aircraft’s are shown as a blip or a trace on the radar screen.In the figure down below , the example shows the aircraft is equipped with a MODE S transponder.



A-320 Transponder

STBY: The Stand By function powers up the transponder and makes it available for operation.

ON : In the ON position, it will send primary information to the radar, that is , it will work like a MODE A transponder.

ALT:If the ALT RPTG is in the ON position , the transponder will send altitude data and will work like a MODE C/ MODE S transponder.

IDENT: All modes (A,C,S) include an ident button.It reveals the identity of the aircraft to the ATC on their radar and helps them locate the aircraft too. For example, when the ATC requests the aircraft to ‘SQUAWK IDENT’ , the pilots need to press the ident button which leads to the aircraft blip on the radar to flash and enables the controller to easily identify the aircraft among many other that are near it.


What are Squawk Codes?

Transponder transmission usually requires a discrete code to identify the aircraft. These codes are assigned by the ATC to each aircraft in their departure clearance.

The squawk codes are 4 digit octal numbers from 0 to 7 and range from 0000 to 7777. Once the pilot receives his squawk code , he has to enter the 4 digit code so that he is visible on the radar .

Let’s take an example, the controller on your departure clearance assigns the pilot to squawk 1234. The pilot can enter 1234 via the numbers shown in the image below and the screen will display the squawk code entered.

Reserved Codes

There are a few transponder codes that have a predetermined meaning and should be used when the aircraft faces that occurrence.

In the above mentioned reserved codes, it is always a good idea to remember the last three codes as they notify the ATC immediately of the problem. As a good rule of thumb, I remember the word ice, that is, interference communication emergency and corresponding to those are the codes, which are, 7500 7600 7700.

Check the image on the right to have a better understanding.

FACT OF THE WEEK: This week we go back to the years where the Wright Brothers were busy making their first powered airplane . A powered airplane would require an engine for the aircraft to take flight. Charles “Charlie” Taylor a mechanic who worked at the Wright Brothers bicycle shop stepped up to help them in their pursuit and became the first man to build an engine that powered an airplane and the first aviation mechanic in history. If it hadn’t been for Charlie the first powered airplane would never have gotten off the ground.

Please click on the link to know more about Charlie Taylor

We are done for this week. I hope you gained some knowledge from this post and if you did please like and share it with your fellow aviators.Please feel free to comment if you have any doubts or suggestions for further posts. Until then stay safe, stay healthy.



Need For Aircraft Lighting

Lighting in an aircraft is another very important parameter that contributes to the safety of the aircraft. If you are driving your car at night without any lights on a dark road ,there is a risk factor involved no matter how skilled a driver you might be.The same applies in aviation, pilots are taught emergency procedures for example a “lights out” landing that is landing without lights during their training in case a need arises for them to deal with it.

Hence it becomes incredibly important for us as aviators to understand the lights installed in our aircraft, the positioning of lights around the plane, their appropriate time of use and the most important that is what if they stop working?. In this post well be looking at the lights installed in an Airbus 320 as I am familiar with the aircraft but most lights in any aircraft always remain the same as a need for uniformity.

Types of Lights Installed

picture credits: Pinterest


  1. The strobe lights are three synchronized flashing lights that are located one on each wing and below the tail cone.
  2. The strobe lights are very bright and flashy and are basically used for identification in the sky.
  3. They are switched ON only when aligned with the runway for take off and switched OFF after exiting the runway at the destination aerodrome.
  4. The strobe lights are not used during taxi as it disrupts the pilots front view if there is an aircraft ahead of him with its strobe lights ON.
  5. In the Airbus 320, there is an AUTO position that enables the strobe lights to be OFF when the landing gear is compressed. This means that if the switch is in the AUTO position, the strobe lights would come ON once airborne and go OFF after landing.
Picture Credit:Aviation technic


  1. Navigation Lights are a compulsion for night flying.
  2. They are also known as position lights as they do not really help pilots in navigation but help determine the relative position of another aircraft in the air.
  3. The navigation lights consists of a steady green light on the right side/ starboard side of the wing and a steady red light on the left side/port side of the wing and a steady white light on the tail of the aircraft.
    • To help remember this, I was taught port wine is red in color.It means that red color light on the left/port side .
  4. To make sure these lights are visible through all directions on the ground and in flight, each light covers a certain angle to be visible according to the ICAO annex 6 that is “OPERATIONS OF AIRCRAFT”. The coverage angles are:
    • A red light projected above and below the horizontal plane on the left side so that it covers 110 degrees.
    • A green light projected above and below the horizontal plane on the right side so that it covers 110 degrees.
    • A white light projected above and below the horizontal plane rearward so that it covers an angle of 140 degrees.
  5. Therefore if you are flying and you see a steady white light ahead of you, it would mean that you are looking at the tail of another aircraft.
  6. The navigation lights help us determining the right of way as well.
    • Looking at figure A below, aircraft A can observe the can view the red light coming from the port side of aircraft B. This helps the pilot of aircraft A to understand that aircraft B has the right of way and it has to stop until clear of the aircraft B .


  1. Logo lights are generally mounted on the upper surface of the horizontal stabilizer and are used for company branding purposes as the lights point towards the company logo painted on the tail fin.
  2. However, the main purpose for the logo lights as all other lights is safety.
    • For example, when an aircraft is on approach, it becomes easier for the aircraft at the holding point to identify the aircraft with the logo light as it gives a 90 degree view.
  3. In the Airbus 320, the logo light is switched on with the navigational light and there is no separate switch for it.
pic credits:IVAO


  1. Wing lights are beam lights fitted on each side of the fuselage and provide lighting on the wing leading edges and on engine air intake.
  2. The main purpose of these lights are to help flight crew, cabin crew and ground personnel detect ice accretion.
  3. The wing lights are also to help detect wing or engine damage and are specially helpful during night operations because of their high beam.


  1. Beacon lights also known as anti collision lights are pulsating red lights fitted on the top and bottom of the fuselage.
  2. The beacon lights in the Airbus 320 are to be switched ON before the engine is started and therefore is included in the before start checklist.
  3. Based on point number 2, it becomes clear that the beacon light also makes the ground personnel aware that the engine is about to be started and the aircraft is ready for push back.
  4. The beacon lights are then switched OFF after the engines have been shut down after landing.
  5. An anti collision is to fitted in an aircraft during night operation to attract attention.
pic credits: QUORA


  1. Taxi light is a bright white light connected to the nose gear strut and goes off automatically once the landing gear is retracted.
  2. As the name suggest, it helps improve the visibility for pilots while taxying and is generally turned ON once the taxi clearance is obtained from ATC.
  3. In the Airbus 320, there is a nose switch that consist of a taxi and takeoff light instead of separate ones but to only make sure the taxi light is ON the toggle switch can be placed to the taxi position as shown below.


  1. The take off light is connected to the nose strut gear and goes off automatically once the landing gear is retracted and is similar to the taxi light but has a wider beam than the taxi light.
  2. The take off light is switched ON just as we line up on the runway and as mentioned above the take off light will go off once the landing gear is up, it is necessary to place the nose switch to the OFF position manually.
picture credit: aviation stack exchange


  1. The runway turn off lights are placed just below the taxi and take off lights on the nose strut gear.
  2. The runway turn off lights point slightly left and right in comparison to the taxi and take off lights as they assist the pilots during turns on taxiways and light up the taxiway and runway edges.
  3. The runway turn off lights are turned ON before taxying and turned OFF just after take off , similar to the taxi lights.


  1. Landing lights are high intensity lights that illuminate the runway surface for take off and landing.
  2. These lights can be mounted on the wing, fuselage on landing gear strut. In the Airbus 320, the landing lights are mounted in the leading edge of the wing and hence they extend and retract in the wing.
  3. The lights control panel doe not have an on and off switch for landing lights.Instead it has an three position switch consisting of extend, retract and off.
  4. The landing lights are extended as soon as possible the take off clearance is obtained and retracted at a certain altitude for example 10,000 ft.Similarly, on arrival the landing lights are extended again at 10,000 ft and retracted immediately after landing.
  5. During night operations, it is necessary that your aircraft is installed with one landing light.


  1. If there is a light that is not operating before take off, you need to check the minimum equipment list to check if the aircraft is safe to take off without the lights not available.
  2. However, there are redundancies to this as well as if your aircraft has 2 navigation light systems then if one fails the other one can be used for operation.

FACT OF THE WEEK: KLM, The Royal Air Transport Company, was founded on October 7, 1909. It is the oldest airline in the world and the oldest still flying under its name. Although the first flight didn’t take to the skies until May 1920, KLM has been a major part of the international airline landscape.Throughout its nearly hundred years of existence, KLM’s commitment to innovation has been constant.This doesn’t just apply to its fleet either. The airline has also proved pioneering with its use of social media, introducing the first social media-driven flight schedule.

This is it for this weeks post.I hope you liked it and gained some knowledge out of the post. If you did please don’t forget to share it with your fellow aviators. Please feel free to share your views and any advice or recommendations on topics you would like to read. Until next week, stay safe and stay healthy.