King Air C90GTi, Pilot Training Manual

Page: 478 / 557

TIME OF USEFUL
CONSCIOUSNESS
In the event of decompression at altitude,
the primar y need is for oxygen to prevent
hypoxia. Hypoxia is the lack of adequate
oxygen to keep the brain and other body tis-
sue functioning properly. Early symptoms
of hypoxia are an increased sense of well-
being, poor coordination, impaired think-
ing, unusual fatigue, and a dull headache.
Therefore, the crew must act quickly to don
oxygen masks and supply oxygen to the pas-
sengers before the onset of hypoxia.
T h e C A B I N A LT H I a n n u n c i a t o r i l l u m i -
nates when cabin altitude exceeds 12,500
f e e t , s h o u l d t h e r e d C A B I N A LT H I a n -
nunciator illuminate due to inadequate cabin
pressure, or loss of pressurization at high
altitudes, crew and passengers should don
oxygen masks immediately and descend to
a safe altitude.
T h e Ti m e o f U s e f u l C o n s c i o u s n e s s t a bl e
(Table 17-2) shows the average time of use-
ful consciousness available at various alti-
t u d e s . T h i s i s t h e t i m e f r o m t h e o n s e t o f
hypoxia until loss of effective performance.
Individuals may differ from that shown in
the table. Using the Emergency Descent pro-
cedure in the Emergency Procedures sec-
tion of the
POH , a ver y rapid descent can
minimize the exposure to hypoxia.
KING AIR C90GTi/C90GTx PILOT TRAINING MANUAL
17-7
FOR TRAINING PURPOSES ONLY
17
OXYGEN
SY
STEM
Table 17-2. TIME OF USEFUL
CONSCIOUSNESS
CABIN PRESSURE TUC
ALTITUDE
30,000 FEET 1-2 MINUTES
25,000 FEET 3-5 MINUTES
22,000 FEET 5-10 MINUTES
12-18,000 FEET 30 MINUTES OR MORE
CYLINDER
VOLUME
CU. FT.
NUMBER OF PEOPLE USING *
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
DURATION IN MINUTES
22 151 75 50 37 30 25 21 18 16 15 13 12 11 10 10
49 334 167 111 83 66 55 47 41 37 33 30 27 25 23 22
66 454 227 151 113 90 75 64 56 50 45 41 37 34 32 30
* THE PILOT AND COPILOT ARE EACH COUNTED AS 2 PEOPLE. CHART DURATIONS ARE
BASED ON CREW USING A NORMAL SETTING FOR 20,000 FEET CABIN ALTITUDES AND
BELOW, AND 100% SETTINGS FOR CABIN ALTITUDES ABOUT 20,000 FEET.
Table 17-1. OXYGEN DURATION (MINUTES)