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AIM 

6/17/21 

10,000 feet during the day, and above 5,000 feet at 
night. The CFRs require that at the minimum, flight 
crew be provided with and use supplemental oxygen 
after 30 minutes of exposure to cabin pressure 
altitudes between 12,500 and 14,000 feet and 
immediately on exposure to cabin pressure altitudes 
above 14,000 feet. Every occupant of the aircraft 
must be provided with supplemental oxygen at cabin 
pressure altitudes above 15,000 feet. 

b.  Ear Block. 

1. 

As the aircraft cabin pressure decreases 

during ascent, the expanding air in the middle ear 
pushes the eustachian tube open, and by escaping 
down it to the nasal passages, equalizes in pressure 
with the cabin pressure. But during descent, the pilot 
must periodically open the eustachian tube to 
equalize pressure. This can be accomplished by 
swallowing, yawning, tensing muscles in the throat, 
or if these do not work, by a combination of closing 
the mouth, pinching the nose closed, and attempting 
to blow through the nostrils (Valsalva maneuver). 

2. 

Either an upper respiratory infection, such as 

a cold or sore throat, or a nasal allergic condition can 
produce enough congestion around the eustachian 
tube to make equalization difficult. Consequently, the 
difference in pressure between the middle ear and 
aircraft cabin can build up to a level that will hold the 
eustachian tube closed, making equalization difficult 
if not impossible. The problem is commonly referred 
to as an “ear block.” 

3. 

An ear block produces severe ear pain and 

loss of hearing that can last from several hours to 
several days. Rupture of the ear drum can occur in 
flight or after landing. Fluid can accumulate in the 
middle ear and become infected. 

4. 

An ear block is prevented by not flying with 

an upper respiratory infection or nasal allergic 
condition. Adequate protection is usually not 
provided by decongestant sprays or drops to reduce 
congestion around the eustachian tubes. Oral 
decongestants have side effects that can significantly 
impair pilot performance. 

5. 

If an ear block does not clear shortly after 

landing, a physician should be consulted. 

c.  Sinus Block. 

1. 

During ascent and descent, air pressure in the 

sinuses equalizes with the aircraft cabin pressure 
through small openings that connect the sinuses to the 
nasal passages. Either an upper respiratory infection, 
such as a cold or sinusitis, or a nasal allergic condition 
can produce enough congestion around an opening to 
slow equalization, and as the difference in pressure 
between the sinus and cabin mounts, eventually plug 
the opening. This “sinus block” occurs most 
frequently during descent. 

2. 

A sinus block can occur in the frontal sinuses, 

located above each eyebrow, or in the maxillary 
sinuses, located in each upper cheek. It will usually 
produce excruciating pain over the sinus area. A 
maxillary sinus block can also make the upper teeth 
ache. Bloody mucus may discharge from the nasal 
passages. 

3. 

A sinus block is prevented by not flying with 

an upper respiratory infection or nasal allergic 
condition. Adequate protection is usually not 
provided by decongestant sprays or drops to reduce 
congestion around the sinus openings. Oral decon-
gestants have side effects that can impair pilot 
performance. 

4. 

If a sinus block does not clear shortly after 

landing, a physician should be consulted. 

d. Decompression Sickness After Scuba 

Diving. 

1. 

A pilot or passenger who intends to fly after 

scuba diving should allow the body sufficient time to 
rid itself of excess nitrogen absorbed during diving. 
If not, decompression sickness due to evolved gas can 
occur during exposure to low altitude and create a 
serious inflight emergency. 

2. 

The recommended waiting time before going 

to flight altitudes of up to 8,000 feet is at least 
12 hours after diving which has not required 
controlled ascent (nondecompression stop diving), 
and at least 24 hours after diving which has required 
controlled ascent (decompression stop diving). The 
waiting time before going to flight altitudes above 
8,000 feet should be at least 24 hours after any 
SCUBA dive. These recommended altitudes are 
actual flight altitudes above mean sea level (AMSL) 
and not pressurized cabin altitudes. This takes into 
consideration the risk of decompression of the 
aircraft during flight. 

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Fitness for Flight