Click here to find Aerodynamics on the App Store!

So, what is HYPOXIA?

Hypoxia is defined as lack of Oxygen in the body tissues due to decreased quantity and molecular concentration. In aviation, it occurs due to fall in partial pressure of Oxygen in the inspired air with increasing altitudes, beyond the possible human physiological compatibility.

Conventionally, hypoxia is classified into four different types:-

Hypoxic Hypoxia. This can occur due to reduction of a partial pressure of Oxygen in the inspired air; reduction in alveolar ventilation or hypoventilation; alveolar capillary diffusion block; or,  ventilation perfusion defects due to lung diseases.

Anaemic Hypoxia.  This results when there is a reduction in Oxygen carrying capacity of the blood due to decreased haemoglobin content. This is commonly due to poor nutritional state. Carbon monoxide, nitrates, sulfa drugs etc. could also cause this type of hypoxia by forming stable compounds with haemoglobin and reducing the amount of haemoglobin available to transport Oxygen to the tissues.

Stagnant or Hypokinetic Hypoxia. This form of hypoxia is due to malfunction of the circulatory system where the oxygen carrying capacity of the blood is adequate but there is inadequate circulation of the blood. Conditions such as heart failure, arterial spasm, occlusion of blood vessel, and in aviation pooling of blood in lower limbs during aerial combat manoeuvres (+Gz acceleration) would predispose to stagnant hypoxia.

Histotoxic Hypoxia. This occurs when the utilisation of Oxygen by the body tissues is interfered with. Alcohol, narcotics and certain poisons such as cyanide interfere with the ability of the cells to make use of the oxygen available to them even though the supply is normal in all respects.

Although all the four types of hypoxia may be encountered in flight, the most frequent and important type of hypoxia encountered in aviation is hypoxic hypoxia (a.k.a. Hypobaric hypoxia), caused by breathing air at altitude. The partial pressure of Oxygen in the inspired air progressively reduces as compared to breathing air at sea level. The principal causes of accidental hypoxia in flight are ascent to altitude without supplemental oxygen; failure of personal breathing equipment; or decompression of the pressure cabin.

There are four stages of hypoxia, as per the altitude and the available partial pressure of Oxygen. The stages of hypoxia are as given in table below.

Hypoxia can produce a multitude of effects, with the severity of the effects depending on the degree of hypoxia. It is pertinent to remember that an understanding about hypoxia is vital for the pilots because its onset is insidious and there is no discomfort or pain brought about by hypoxia.

The signs and symptoms of hypoxia become apparent as the degree of hypoxia increases. This includes:-

• Breathlessness/ air hunger
• Excessive yawning
• Tiredness and fatigue
• Euphoria
• Impairment of performing recently learnt task
• Impairment of mental task (learnt tasks)
• Altered sensorium, including loss of consciousness

Hypoxic changes observed are due to:

• Compensatory mechanisms of the body
  • Increase in respiratory rate.
  • Increased depth of respiration
• Impaired cellular functions as a result of decreased oxygen availability
  • Decreased night visual acuity
  • Impaired psychomotor performance

It is important to remember that there are several factors which affect the onset and the severity of the effects of hypoxia. This includes:-

• Altitude.  Higher the altitude, lower is the partial pressure of alveolar oxygen;  hence shorter is the latent period and greater the severity of effects.
• Rate of ascent.  The greater the rate of ascent the more rapid the onset of signs and symptoms of hypoxia
• Duration at Altitude.  The effects of hypoxia are more severe if the duration at altitude is prolonged. This is due to the fact that the effects of hypoxia are cumulative.
• Ambient Temperature.  High or low environmental temperature favours the development of hypoxia.
• Physical Activity.  Physical effort at altitude raises the demand for Oxygen and hence the symptoms of hypoxia are more severe. This fact is to be remembered by aircrew other than pilots too.
• Individuals Susceptibility.  Individuals differ considerably in their ability to withstand hypoxia.
• Physical Fitness.  A high standard of physical fitness is conducive to a better tolerance of hypoxia. Regular physical training improves the tolerance levels.
• Smoking.  Smoking makes an individual more liable to suffer from hypoxia due to binding of haemoglobin with Carbon monoxide present in the smoke. A smoker who smokes prior to sortie has already compromised him-/herself to hypoxic insult, where s-/he is at an apparent altitude of 7,000, 14000, 22000 ft as compared to a non-smoker pilot at sea level, 10000 and 20000 ft, respectively. Be informed that if one smokes three cigarettes before a sortie, it is as if s-/he is already at an equivalent altitude of 8000 feet, with its implications due to compromised vision.
• Organic Diseases.  Effects of hypoxia are more severe in those with disease of the heart, lungs or blood, which interferes with the normal oxygenation and circulation, to restrict adequate physiological compensation.
• Emotional State.  Apprehension and anxiety make an individual more susceptible to the effects of hypoxia.
• Acclimatisation.  Acclimatisation while residing at high altitude raises the individuals ability to withstand hypoxia.
• Equivalent Lung Altitude.  Breathing air at a sea level is associated with a certain partial pressure of oxygen in the lungs (104 mm Hg). By breathing 100% Oxygen, the same partial pressure is brought about at a much greater altitude i.e. at 33,000 ft. The table below shows various equivalent lung altitudes while breathing 100% Oxygen. This concept is found useful in designing the Oxygen system for combat aircraft to ensure adequate oxygenation of the aircrew at different altitude.

If you want to study your all your aeromed and get the answers right everytime, you might want to check out our Aeromed App, especially if your right at the beginning of flight school…

Aeromedical Training and Aerodynamics

Yea, neither have I….

However, I have sat clueless in front of an IP when he asked me that question,… I did that a lot in flight school, and I decided that wasn’t a good course of action, so I took it upon myself to put together a list of all the questions and answers I had ever been asked, or ever thought that I might get asked, and created flashcards out of them, or created little study guides, or something… anything that would help me overcome my stage fright, and get me to pass my checkride…

Let’s look at the different types of Drag forces that act on a helicopter, and some examples of each…

Parasite Drag, Profile Drag, and Induced Drag.

Parasite Drag is incurred from the non-lifting portions of the aircraft. It includes form drag, skin friction, and interference drag associated with the fuselage, engine cowlings, mast and hubm landing gear, wing stores, external load, and rough finish paint. Parasite drag increases with airspeed and is the dominant type at high airspeeds.

So, basically anything that sticks out on the aircraft that isn’t helping the aircraft fly any faster… is parasitic! Or causes Parasite Drag.

Let’s talk about Profile Drag: Profile drag is incurred from FRICTIONAL resistance of the blades passing through the air. It increases slightly at higher airspeeds, but does not change significantly.

Induced Drag is incurred as a result of production of lift. Something has to create lift, and that something is a wing, or a rotor blade. A rotor blade is nothing more than a FIXED WING (like on an airplane) that spins in the air to create lift. Higher angles of attack which produce more lift, also generate downward velocities and vortices that increase induced drag. In rotary wing aircraft, induced drag decreases with increases aircraft airspeed.

I apologize, there really is no good way to memorize which type of drag does what! But if you can remember that non-flying Parasites on the side of the aircraft weigh you down, and the faster you go, the more “parasitic” they will be (causing more drag)… you have 1 down.

Now remember Profile: Think about the profile of the wing chamber… Ok, so now you can remember the profile of the wing chamber is associated with PROFILE DRAG… and PROFILE DRAG is caused by the wing, or any other airfoil on the aircraft! See, this isn’t too hard.

One more, we are almost there….

Thankfully, by process of elmination, you have 1 left, and that’s Induced Drag. Just remember that the airfoil isn’t perfect, either… it helps produce lift, but it’s still dragging through the air, INDUCING drag on the aircraft. Thankfully, as you pick up airspeed, the airfoil helps you more and more as the aircraft becomes much more efficient.

Try this advanced move on one day… your IP will be impressed if you pull this out: Flip an Endurance Chart sideways, and tell your IP that the ups and downs represent the different types of drag. It’s most efficient at a median airspeed where Parasite Drag and Induced Drag come together to give you the most efficient airspeed… also known as your max endurance and max range airspeeds.

Click this link to See Instrument Flight Training Flashcards on the App Store for iPhone and iPad!

Download on iTunes

If your in Flight School at Fort Rucker as an Army Aviator, you will want to check out this 5 & 9 Flashcard Study Guide App for your iPhone or Android device. Not only will you save space in your backpack and flight bag, but you will lighten your load, and be able to carry more documents and apps on your iPhone and iPad than anywhere else. Great way to study no matter where you are!

Download on iTunes

If your an Army Flight School Student at Fort Rucker, you will find this App to be a most valuable resource in your backpack. Use these flashcards to study your 5 & 9 just as you would the paper back flashcards, and save a TON more space!

Download on iTunes

If your an Army Flight School Student at Fort Rucker, you will find this App to be a most valuable resource in your backpack. Use these flashcards to study for your Aeromed and Aerodynamics Academic Tests (or an APART) just as you would the paper back flashcards, and save a TON more space!

Download on iTunes

If your in Flight School at Fort Rucker as an Army Aviator, you will want to check out this 5 & 9 Flashcard Study Guide App for your iPhone or Android device. Not only will you save space in your backpack and flight bag, but you will lighten your load, and be able to carry more documents and apps on your iPhone and iPad than anywhere else. Great way to study no matter where you are!