Ask the Flight Surgeon / By Dr. (LTC) Joseph Puskar: Q: Can we use the Reduced Oxygen Breathing Device (ROBD) for altitude physiology periodic “chamber card” training instead of going to an altitude chamber?
The Joint Service Aircrew Mask-JSF integrates with the F-35 life support system and pilot flight equipment to provide combined chemical-biological and anti-gravity protection. / ARMY.MIL
FS: Initial training is still being conducted in the altitude chamber, but soon even initial altitude physiology training will be done with ROBD for Army rotary wing crews. Fixed wing aviators will continue to use the chamber for initial training, but they too can use ROBD for periodic, five year recertification training. Some adjustments may be made to the altitude training profiles such as more gradual ascents, and lower simulated peak altitudes to give rotary wing aircrews in particular more realistic, less dramatic subjective experiences of the signs and symptoms of hypoxia such as the slowed cognition and reduced reaction times that can often go unnoticed, but still be significant enough to contribute to mishaps.
The ROBD is rapidly becoming the preferred method of hypoxia training around the world. This is due not only to significant acquisition and maintenance cost savings and portability compared to bulky altitude chambers, but also improved safety compared with the high altitude chamber runs. Primitive versions of the device were in use predating World War II. A standard oxygen mask and aviator’s helmet are worn, and the oxygen percentage of the inhaled gas is reduced to simulate the relative hypoxia effects of ascending to various altitudes. A nice feature is that a computerized flight simulator of virtually any aircraft in the inventory can easily be set up in front of it so the pilots can test their skills under hypoxia conditions approximating the effects at any practical atmospheric altitude.
The Training Profile
The traditional training profile with ROBD has consisted of rapid onset of hypoxia, for example climbing from 8,000 to 25,000 feet at a rate of 12,000 feet per minute. A recent Air Force study using experienced fighter pilots found that by using a more gradual rate of “ascent,” or reduction of inhaled oxygen percentage, the recognition of the onset of subjective, self-reported symptoms of hypoxia such as numbness, tingling, chest pressure, difficulty breathing, anxiety or euphoria, and the objective findings of heart rate and blood oxygen saturation differed significantly from the more rapid ascents. This is significant for rotary wing crews, and especially so when operating in mountainous regions where gradual ascents following the terrain is often the standard mission. In the gradual climb profile, blood oxygen saturations dropped much lower before two critical events: initial recognition of hypoxia onset and activation of the emergency oxygen system. Similar to Gillingham illusion spatial disorientation where the shallower bank angles are usually the most disorienting, the gradual climbs seem to be more insidious in fooling the senses that things are fine when in fact there is significant functional impairment. This is likely due to the much more subtle and less dramatic effects on the senses and self-perception of cognitive decline. The Air Force researchers recommend that a slow ascent profile be added to the training, and since this is a closer simulation of the operating environment for Army helicopter pilots, this type of profile may be included in hypobaric training of the near future.
Army aviators currently get chamber training as part of initial fixed wing training or IERW, and the subsequent, five-year interval retraining can then be done with ROBD. The Air Force training regimen is essentially the same. Naval aviators go through initial altitude chamber training, and then most have the option of going through either ROBD or chamber refresher training four years after that. Navy high performance jet aircraft aviators will continue with chamber re-certifications for at least the foreseeable future.
Rapid Decompression
One disadvantage of the ROBD is the difficulty in simulating rapid decompressions and other physical effects of low pressure environments. For this reason, fixed wing aviators will continue to train in the chambers for at least the initial phase of physiologic training, and the Air Force is working on a composite system that will incorporate elements of ROBD with the conventional altitude chambers. This new technology may be available for use to all the branches in the near future, so stay tuned for some new developments in this field over the next few years. A recent U.K. Royal Air Force experiment with rapid decompressions at very high pressure altitudes found significant, rapid impairment in test subjects made vulnerable by large lung volumes despite immediately switching to 100% oxygen. This was due to very rapid nitrogen accumulation in the lungs due to the sudden partial pressure gradient increase with decompression, and the subjects not purging their lungs quickly enough with oxygen. Taking two full, deep breaths of oxygen right after donning the mask remedied this situation, so do the same if ever experiencing a rapid decompression!
Safe flying!
Question for the Flight Surgeon?
If you have a question you would like addressed, email it to This email address is being protected from spambots. You need JavaScript enabled to view it.; we’ll try to address it in the future. See your unit flight surgeon for your personal health issues. The views and opinions offered are those of the author and researchers and should not be construed as an official Department of the Army position unless otherwise stated
Dr. (LTC) Joseph Puskar is a flight surgeon at the U.S. Army Aeromedical Center, Fort Rucker, AL.
The Joint Service Aircrew Mask-JSF integrates with the F-35 life support system and pilot flight equipment to provide combined chemical-biological and anti-gravity protection. / ARMY.MIL
