High Altitude Testing

Several Approaches to Testing

Depending on the scope of your program, there can be several ways to approach this testing. One manufacturer has based their operations out of a lower altitude airport and then flown to the higher airport for the testing and returned the same day. If your test program can support this, it is the least invasive to the team from a physiological point of view, since the crew doesn’t necessarily have to become “acclimated” to the full target altitude. It is recommended that this location be at an intermediate altitude to help with acclimation and lessen the total pressure change on each flight. But this approach has its downsides too. There is the added travel time to and from the test site (and associated costs), and often you may need to stop and do the customs, both of which eats into your test day. You may also suffer from weather changes enroute. Finally, if something should go wrong, you may not have the right maintenance people/equipment there and then there would be the burden of last minute travel issues (hotels, transportation, visas, etc.).

However, if you have tests such as cold engine starts that require an overnight cold soak, then you may have to deploy and operate at the higher altitude airport. Advantages include no travel time to the test site, no risk of failures stranding you away from support and no risk of weather issues popping up that aren’t easily waited out, However, this approach puts the entire test team under the most physiological stress and they need to be acclimated to be in peak performance. This may extend your deployment by several days.

With either approach stated above, you may be staying in a foreign country. This brings up other medical-related risks such as gastro-intestinal illnesses caused by local food/water and local diseases. The longer you stay in the foreign locale, the higher chance someone may get sick.

  • Research where you are going in case there are certain vaccines recommended or required to have in order to travel there.
  • Drink bottled beverages only.
  • Be cautious about sampling the local cuisine. Especially avoid street vendors.


With either approach the main concern is physiology issues related to the high altitude. The body doesn’t like it at that high altitude (low pressure and lack of oxygen) and can cause several different medical conditions, with hypoxia on the top of the list. Extended time in hypoxic conditions can also lead to what is called “Acute Mountain Sickness” (AMS). This can be a life threatening condition if not diagnosed and treated in a timely fashion. The cause of AMS is the lower level of oxygen available at altitude. With a few hours of exposure to low oxygen levels, without sufficient acclimatization, this lack of oxygen can lead to a condition known has pulmonary edema, where the lung tissues become stiff and full of fluid. Your risk of experiencing acute mountain sickness is greater if you live near sea level and are unaccustomed to higher altitudes. Anyone who makes a rapid ascent and has a prolonged stay at altitudes greater than 10,000 feet above sea level is subject to AMS.

The very first and foremost mitigation is that ALL flight test crewmembers have gotten education in flight physiology, to include a high altitude chamber ride. Everyone needs to know how this affects you and what your hypoxia symptoms are. Believe it or not, this training is FREE! The FAA’s civil aeromedical institute (CAMI) in Oklahoma City, OK conducts a one-day physiology class that includes ground school and an altitude chamber ride (or new nitrogen enriched chamber that simulates the low oxygen partial pressure). You just need to get there to take the class.


Some early symptoms you may experience with hypoxia or AMS:

  • Dizziness
  • Headache
  • Feeling unusually hot (flushed)
  • Disturbed vision (blurry or tunnel)
  • Confusion
  • Muscle aches
  • Tingling in extremities
  • Insomnia
  • Nausea and vomiting
  • Irritability
  • Loss of appetite
  • Swelling of the hands, feet and face
  • Rapid heartbeat
  • Shortness of breath with physical exertion

If any of those symptoms appear, some interventions include:

  • Stop any physical activity and rest
  • Ensure well hydrated
  • Return to a lower altitude if possible (or re-pressurize the aircraft)

Symptoms of sever altitude sickness, requiring immediate medical attention may include:

  • Uncharacteristic coughing
  • Chest congestion
  • Pale complexion and skin discoloration
  • Inability to walk or lack of balance
  • Social withdrawal

Coughing up blood, or loss of consciousness are late signs of AMS that may indicate a fatal outcome.


Some or all of the below mitigations can be used to help acclimate to the high altitude or mitigate the dangers. Whether it is hypoxia or AMS, most mitigations are the same.

  • It is recommended to allow at least 1-2 days to allow your body to acclimate to the higher altitude. Of course longer is better, but most physicians recommend at least 48 hours.
  • If you have choices in personnel, take the more physically fit people and non-smokers if possible. If you have any significant medical issues (such as heart/lung disease or anemia), see your doctor before going.
  • Abstain from any significant physical activity. Nothing more than normal walking is recommended. Even walking stairs can be tough. Take the elevator if you can. (I can attest that just climbing the flight stairs at 13K’ will wind you!). You may run at home, but at 13K’ it can put major stress on your body. Don’t be lulled by seeing locals jogging around, they are acclimated! Just give up the workout for the duration.
  • Abstain from alcohol intake.
  • Medications: Like alcohol, sleeping medications such as Ambien, and some Anti-Hypertensive medications will slow your rate of breathing in your sleep and make you more susceptible to AMS, and render you more likely to experience the serious consequences associated with the disorder. Check with your doctor if you’re taking any medications.
  • You may have trouble sleeping and from my experience in La Paz, the better hotels offered oxygen to use in your room to help with sleeping and acclimation and to address symptoms like headaches.
  • Keep yourself well hydrated and nourished (frequent high carb meals recommended).
  • Crewmembers participating in the test need to wear oxygen whenever the cabin altitude is above 8,000 feet (typical pressurized cabin). This could be an extended period so care needs to be taken to ensure enough oxygen is onboard, whether it is in onboard systems or separate bottles.
  • Return to lower altitudes to sleep (first scenario described above).

There are is a medication you can take that will help with acclimation and lessen altitude sickness. You start taking it several days before you leave. Its generic name is Acetazolamide (common brand name: Diamox). It is a prescription drug so you need to see a doctor to get it. There are some side effects as it is a diuretic, so the doctor can analyze whether the benefits outweigh the risks in your particular case. Pilots should contact their doctor to document that they are on this medication for prevention of altitude sickness (not some other condition which may be disqualifying) and it is recommended they send an email to their regional flight surgeon stating this, in case anything should happen.

This short article was put together with inputs from several members of the Flight Test Safety Committee and reviewed by an FAA aeromedical examiner. If you have anything to add, please email me at: This email address is being protected from spambots. You need JavaScript enabled to view it. or phone me at 425-917-6518

John Hed
FAA Flight Test Engineer
Seattle Aircraft Certification Office (SACO)